Cumitech 23: Infections of the Skin and Subcutaneous Tissues

CUMITCCH 23

Cumitech I,4 * Blood Cultures II * June 1982 Cumttech ?A * Laboratory Diagnosis of Urmary Tract Infections * March 1987 Cumitech 3 * Practical Qualrty, Control Procedures for the Clmical Microbiology Laboratory September 1976 Cumitech 4 * Laboratory Diagnosis of Gonorrhea * October 1976 Cumitech 5 * Practical Anaerobic Bacteriology * April 1977 Cumitech 6 * Neu De\,elopments in Antimicrobial Agents Susceptibility Testmg * September 1977 Cumttech 7A * Laboratory Diagnosis of Lo\+ er Resptratory Tract Infections * September 1987 Cumitech 8 * Detection of Microbial Antigens by Counterimmunoelectrophoresis * December 1978 Cumttech 9 * Collectton and Processing of Bacteriological Specimens * August 1979 Cumitech 10 * Laboratory Diagnosis of Upper Respiratory Tract Infections * December 1979 of Fungi in the Climcal Cumitech 11 * Practical Methods of Culture and Identification hlicrobiology Laboratory * .4ugust 1980 Cumitech 12 * Laboratory Dtagnosis of Bacterial Diarrhea * October 1980 Cumitech 13 * Laboratory Dtagnosts of Ocular Infections * May 1981 Cumitech 14 * Laboratory Diagnosis of Central Nervous System Infections * January 1982 Cumitech 15 * Laboratory Diagnosis of Viral Infections * March 1982 Cumitech 16 * Laboratory Dtagnosis of the Mycobacterioses * March 1983 Cumitech 17 * Laboratory Diagnosis of Female Genital Tract Infections * August 1983 Cumitech 18 - Laboratory Diagnosis of Hepatitis Viruses - January 1984 Cumitech 19 * Laboratory Diagnosis of Chlamydial and Mycoplasmal Infections * August 1983 Cumitech 20 * Therapeuttc Drug Momtoring: Antimicrobial Agents * October 1984 Cumitech 21 * Laboratory Diagnosis of Viral Respiratory Disease * March 1986 Cumttech 22 + Immunoserology of Staphylococcal Disease * August 1987

Cumitechs should Cumitech 23, Infections Society for Microbiology,

be cited as follows, e.g.: Simor, A. E., F. J. Roberts, and J. A. Smith. 1988. of the skin and subcutaneous tissues. Coordinating ed.. J. A. Smith. American Washington, D.C.

Editorial Board for ASM Cumitechs: Steven C. Specter. Chapman: Carl Abramson. Willram J Martone, John E. McGowan, Jr, Glenn D. Roberts, James W. Smrth, John A. Smrth, Thomas J Trnghrtella, and Alrce S. Werssfeld

The purpose of the Cumitech of-the-art operating procedures routine

or new methods. TQp, ~QL%!uP,~ gx~,n. xe

series IS to provide consensus recommendations by the authors as to appropriate statefor clinlcal microbiology laboratories which may lack the facilities for fully evaluating oat prQpQsed

Copyright

as “standard”

% 1988

methods.

Amencan Society 1913 I St NW

Washmgton.

DC 20006

for MIcrobiology

INFECTIONS OF THE SKIN AND SUBCUTANEOUS TISSUES ANDREW Toronto, FREDERICK Columbia,

E, SIMOR, Department of Microbiology, Ontario M5G 1x5, Canada

Mount

J. ROBERTS, Division of Microbiology, Vancouver, British Columbia VSZ lM9,

JOHN A. SMITH, Division of Microbiology, Columbia, Vancouver, British Columbia

Hospital,

and University

Hospital,

and

of Toronto,

Vancouver Canada

General

Vancouver General V5Z IM9, Canada

Hospital,

and University

of British

Hospital,

and

of British

COORDINATING JOHN A. SMITH, Division of Microbiology, Columbia, Vancouver, British Columbia

Sinai

University

of British

EDITOR

Vancouver General V5Z lM9, Canada

University

Infections may also be acute or chronic. An acute staphylococcal furuncle lasts a few days, whereassomechronic fungal infections may last for months or years. Infections in which the primary focus is in deeper structures may exhibit striking cutaneous manifestations, further complicating classification of infections, e.g., toxic shock syndrome, meningococcal septicemia, and many other infections. Clinical classification was adopted as the method for organizing the material for this CUmitech. To this end we selected those diseases that may be classified as superficial erythematous infections, ulcers and nodules, sinustracts, burns, simple postoperative wounds, complicated wound infections, and bites. Each classof infection hasbeen highlighted with regard to the main clinical features, the common causative organisms,and a practical approach to laboratory diagnosis. We have purposely excluded the diseasesthat either are systemicor have a noncutaneousprimary focus. Cutaneousmanifestationsof endocarditis, ecthyma gangrenosa,secondary syphilis, and viral exanthemataare someexamplesof this large group of diseases.Similarly, we have excluded infections in which diseaseaffecting the skin is mediated by toxins, as well as parasitic infestationsand ophthalmicand genital infections. The examination of all of these subjects would require a volume more extensive and diverse than is intendedfor the Cumitechformat. Laboratory procedures that are described in another Cumitech are not duplicated in this volume.

The skin (Fig. 1) is the most accessibleorgan of the body, the one most readily traumatized and therefore the one subjected most frequently to the risk of infection. Composedof a superficial zone called the epidermis and a deeper zone called the dermis, it is an organ that is richly endowed with specialized structures and functions. Body temperature and fluid control are influenced by skin, as are sensory functions such as touch and pain. Hair follicles, sebaceousglands, and sweat glands open to the skin surface. Beneath the dermis is a layer of subcutaneousfat, below which sit the thin fascial membranes that cover muscles, ligaments, and other connective tissues. Fascial planescreate spacesin various parts of the body, including the head and neck, fingers, hands, and feet. The fascia is a barrier that determines the extent to which infections may spread but may also create therapeutic challenges, due to impenetrability, which may have to be met surgically. This Cumitech is concerned with someof the common infections that involve skin and subcutaneous tissues. This is a complex subject involving a great diversity of organisms and of etiological and pathogeneticmechanisms.These infections are classifiedas primary and secondary. Primary infections occur de novo in patients with no obvious portal of entry, e.g., erysipelas. Secondary infections arise as complications of injury to the skin such as abrasions, surgical trauma, or penetrating wounds.Theseinfections are either monomicrobial, as in staphylococcal wound infection, or polymicrobial, as in some gangrenousconditions causedby microaerophilit streptococci and anaerobes.Secondary infections may be localized or extensive, depending on the extent of the underlying diseaseor precipitating trauma.

SUPERFICIAL ERYTHEMATOUS LESIONS The common infecting microorganisms and laboratory diagnosticmethodsin superficial erythematousinfections are listed in Table 1. 1

SIMOR ET AL.

CUMITECH

23

aureus are considered to be the most common etiological agents. Aeromonas and Vibrio speciesmay causean acute cellulitis Epiderrnls following introduction of the organismthrough a wound or laceration sustainedwhile swimming Dermis in fresh or salt water. Haemophilus influenzae cellulitis is a relatively uncommon but distinctive form of infection often associated with Subcutaneous fat bacteremia and typically affecting children 6 Fascia months to 3 years of age (31). The diagnosisof cellulitis or erysipelas can generally be made clinically, and knowledge of FIG. 1. Section through normal skin. the usual bacterial pathogenscan guide empiric antimicrobial therapy. The treatment of choice for erysipelas is penicillin (erythromycin for a Erysipelasand Cellulitis Erysipelas is a superficialinfection of the skin, patient with penicillin allergy). Empiric treatusually caused by group A streptococci, al- ment of cellulitis should be with a penicillinasethough rare casesdue to group C or group G resistant penicillin (e.g., cloxacillin) or a cephastreptococci have also been described. The in- losporin effective against both Streptococcus fection primarily involves the dermis and the pyogenes and S. aureus. In children, therapy most superficial parts of the subcutaneoustis- should include antimicrobial coverage for H. The choice of antimicrobial therapy sues,with prominent involvement of superficial in.uenzae. lymphatics. Erysipelas presents as a painful, may be modified in light of subsequentmicrobifiery red, edematous,and indurated areaof skin, ological findings. occasionally with smallvesiclesor bullae on the surface. There may be a “peau d’orange” (or- Laboratory ange rind-like) appearance due to the marked Anecdotal reports have suggestedthe potential superficial cutaneousedema. A key clinical fea- value of needleaspiration for the bacteriological ture is the raised border of the skin lesion that is diagnosisof soft tissueinfections (40). The techsharply demarcated from adjacent normal or nique for aspiration involves disinfecting the site uninvolved skin. The acute onset of fever and and aspiratingthe advancing margin of erythema chills is prominent, and regional lymphadenop- with a 22. or 23.gaugeneedleattached to a 3- or athy is often present. 5-ml syringe. If the initial aspirationfails to proCellulitis is a diffuse, spreadinginfection in- vide material for culture, 0.1 to 0.5 ml of sterile, volving the loose connective tissue of deeper nonbacteriostaticisotonic salinemay be injected layers of the dermis. It is characterized by local subcutaneously,followed immediatelyby a repeat pain, tenderness,erythema, and edema, associ- attempt at aspirationwithout removing the needle ated with fever, chills, and regional lymphade- from the injection site. If, after this, no fluid is nopathy. Unlike erysipelas, the margins of an recovered, the needleand syringe may be rinsed area of cellulitis are ill defined, not elevated or with broth by drawingthe culture mediumthrough sharply demarcated. Group A streptococci and the needle into the syringe, and the tip of the Staphylococcus

MUSCl9

TABLE Diseases and syndromes

Common

1. Superficial erythematous infections causative

organisms

Ery sipelas Cellulitis

Group A streptococci Group A streptococci, S. aureus

Erysipeloid Impetigo Folliculitis , furunculosis, carbuncles Paronychia Whitlow

E. insidiosa Group A streptococci, S. aureus S. aureus, P. aeruginosa, Proteus spp. S. aureus, Candida spp. S. aureus, herpes simplex virus

Superficial mycoses

Candida spp., E. floccosum, Trichophyton sp., Microsporum

Erythrasma

C. minutissimum

Laboratory

SP-

diagnostic

methods

Gram stain, culture on blood agar and chocolate agar, MacConkey agar, Trypticase soy broth Culture on blood agar Gram stain, culture on blood agar Gram stain, blood agar, MacConkey agar Gram stain, culture on blood agar Gram stain, culture on blood agar, virus culture, fluorescent-antibody staining, electron microscopy KOH preparation, culture on Sabouraud dextrose medium with chloramphenicol and cycloheximide Wood’s lamp, Gram stain, tissue culture

CUMITECH

23

SKIN

AND

SUBCUTANEOUS

TISSUE

INFECTIONS

3

needle may be streaked across the culture plate. Although advocated as a method for obtaining a bacteriological diagnosis (21), the value of needle aspiration in the management of erysipelas or cellulitis has not been clearly demonstrated. In retrospective reviews of cellulitis in adults, soft tissue aspiration yielded a positive culture in only 5 to 12.5% of specimens tested (14,15). A prospective study of techniques for the microbiological evaluation of cellulitis in 50 adult patients found that only 4% of blood cultures, 10% of soft tissue aspirates, and 20% of punch skin biopsies were positive ( 19). In children with cellulitis, where infection is often due to H. influenzae type b, there may be a higher percentage of positive cultures of blood or soft tissue aspirate (12, 31). Aspirates should be cultured on blood agar, on chocolate agar, and in a broth such as Trypticase (BBL) soy broth.

vesicles pustulate and rupture. The purulent discharge dries, forming characteristic, thick, amber- or honey-colored crusts surrounded by an erythematous margin or halo. Cultures of the lesionsyield group A streptococci in pure culture or mixed with S. aureus, although the staphylococci are generally considered to be “secondary invaders” rather than primary pathogens. Impetigo occasionally has been attributed to infection due to group C or G streptococci. Recommendedtherapy is with penicillin (erythromycin for a patient with penicillin allergy). Bullous impetigo, usually caused by S. aureus, is less common than streptococcal impetigo and usually occurs in neonatesand infants. The lesionsbegin as vesicles and then typically form groupsof superficial, flaccid bullae (0.5- to 3.0.cm diameter) with minimal or no surrounding erythema. The bullae are thin walled and Erysipeloid rupture easily, revealing an underlying patch of A relatively uncommon nonsuppurative cellu- raw skin resemblinga second-degreeburn. The exudate may be serousor purulent and forms a litis due to the gram-positive bacillus Erysipelothrix rhusiopathiae (E. insidiosa) is primarily thin brown crust on drying. The treatment of seen as an occupational diseaseof fishermen, choice is with a penicillinase-resistantpenicillin fish handlers, butchers, and abbattoir workers. pending bacteriological results. The hands and fingers are the major sites of involvement. The lesion typically presentsas a Laboratory The diagnosisof impetigo is generally made painful, purplish area of inflammation, with an erythematous advancing edgebut central pallor. by noting the typical clinical appearanceof the Unlike streptococcal or staphylococcal cellu- lesions. Bacteriological confirmation is not usulitis, local suppuration, fever, and constitutional ally required, but after*the skin lesion has been symptomsare uncommon.Penicillin is the treat- cleaned with 70% alcohol, the crust may be ment of choice; erythromycin is a suitable alter- removed and the base of the lesion cultured. native in a patient with penicillin allergy. Serological evidence of recent group A streptococcal infection may occasionally be useful for Laboratory confirming the diagnosis retrospectively. The Gram stain or culture of superficial wound detection of antibody to streptococcal DNase B drainageis usually negative. The bacteriological is a more sensitive indicator of group A streptodiagnosis of erysipeloid can be confirmed by coccal skin infection than is the anti-streptolysin culture of a full-thickness skin biopsy taken at 0 titer, probably becauseof inhibition of strepthe margin of the lesion. Details regarding the tolysin 0 by lipids in the skin at the infection site. Culture on blood agar is adequate. isolation and identification of E. rhusiopathiae have been describedpreviously (42). Briefly, the Folliculitis, Furunculosis,and Carbuncles biopsy should be placed in 5 ml of Trypticase soy broth, incubated aerobically or in CO, at 35 Folliculitis, furunculosis, and carbuncles are to 37”C, and subcultured onto blood agar daily localized cutaneous abscessesthat are distinfor 5 days or until a positive subculture is guishedby their size and extent of subcutaneous obtained. involvement (Fig. 2).

Impetigo Impetigo is a superficial intra-epidermalinfection of the skin, producing erythematouslesions that may be either bullous or nonbullous. Nonbullous impetigo is usually caused by group A streptococci, whereas S. aureus has been associated with the bullous form of disease. The lesions of nonbullous impetigo begin as small, erythematous papules,which then form vesicles (l- to 2-cm diameter). Within a few davs. the

Folliculitis Folliculitis is infection and inflammation of hair follicles usually precipitated by blockage of the follicle or by minor local trauma (Fig. 2). The infection is characterized by dome-shapedpapules or pustules, pierced by a hair and surroundedby a rim of erythema. The inflammation is nearly always due to S. aureus, and although the etiology of the folliculitis may be confirmed bv culture of pusor exudate from the lesion. this

4

SIMOR ET AL.

CUMITECH

23

FIG. 3. Fur-uncle (boil) destroying tissue around a hair follicle.

deeper and more extensive, often presenting as multiple subcutaneousabscessesinvolving several hair follicles and sebaceous glands and is not usually necessary. Treatment with local which drain along hair follicles (Fig. 3 and 4). measures,suchas salinecompressesand topical Carbuncles may be associated with fever and antibiotics (e.g., clindamycin), is usually suffi- malaiseand may be complicated by cellulitis or bacteremia. Both furuncles and carbuncles occient. Other, much less common, causesof follicu- cur on skin subject to friction and perspiration litis include gram-negative folliculitis due to and where hair follicles are present (e.g., butmembersof the family Enterobacteriaceae (es- tocks, axillae, neck, and face). S. aureus is the pecially Proteus species). This may occur in most frequent pathogen. Treatment with warm patients with acne vulgaris who have received compressesis usually adequate for small localoral antibiotics for prolonged periods of time. ized furuncles. Antistaphylococcal antibiotics, Recently, outbreaks of folliculitis associated such as cloxacillin and clindamycin, may be with the use of whirlpools, swimmingpools, and required in the presence of fever or if there is hot tubs contaminated with large numbers of surroundingcellulitis, especially if the fur-uncles Pseudomonasaeruginosahave been recognized or carbunclesare located about the mid-face. (16, 30). The cutaneous eruption consists of itchy, erythematous papules or papulopustules. Laboratory The microbiological diagnosis can generally The rash is not unique in appearancebut does have a characteristic distribution, primarily in- be madeby culturing pus from the lesionsaerovolving buttocks, hips, thighs, and axillae. bically on blood agar and MacConkey agar at Theseare areaswhere apocrine sweat glandsare 35°C for 18 h. located and areas which tend to be occluded Paronychia when bathing suits are worn. In addition to the Paronychia is a superficial infection of the nail rash, many individuals complain of a low-grade fever, headache, malaise, earache (due to ac- fold that may be acute or chronic. Acute infeccompanying otitis extema), and painful breasts tions are due to S. aureus, which may be cul(due to mastitis). The characteristic distribution tured from purulent drainage. Treatment with of the rashin associationwith a recent history of warm compressesis usually adequate, although exposure in a whirlpool, hot tub, or swimming sometimes incision and drainage may be repool is helpful in making the diagnosis. The quired. Chronic paronychia is often associated illness may last several weeks, but is generally with frequent immersion of hands in dishwater self-limiting with spontaneoushealing, and no and is usually due to Candida species. Treatment of Cundida infection of the skin and nail specific therapy is required. FIG. 2. Folliculitis in a hair follicle.

Laboratory

In staphylococcal folliculitis, bacteria are usually not seen on Gram-stained smear and culture. However, in pseudomonalfolliculitis, although P. aeruginosa may be cultured from larger pustules, cultures are often negative. Furunculosis

and Carbuncles

A furuncle is an abscessthat begins in a hair follicle as a firm, tender, red nodule that becomes painful and fluctuant. A carbuncle is

FIG. 4. Carbuncle, a complex of abscesses tiecting several hair follicles.

CUMITECH

23

SKIN AND SUBCUTANEOUS

bed include elimination of the precipitating cause and a 2% solution of gentian violet in ethanol applied directly to the lesion. Other antifungal agentssuch as nystatin and clotrimazole may be used. Laboratory The microbiological diagnosis may be confirmed by culturing aspirated or drained pus aerobically on blood agar as describedabove. Whitlow Whitlow is a purulent lesion on the distal phalanx of a finger, often causedby a penetrating wound by a small sharp object. S. aureus is often the cause. It should be noted that a similar lesion may be causedby herpessimplex virus and that herpetic whitlow is often misdiagnosed as a bacterial paronychia. Clinical features in herpetic whitlow that help distinguish it from pyogenic infection include the following: (i) medical, paramedical, or dental occupation; (ii) presence of “satellite” vesicles; (iii) pain disproportionate to physical findings; (iv) nontense pulp space; and (v) serous rather than purulent vesicular fluid. Treatment for staphylococcal infection is with a penicillinase-resistant penicillin (e.g., cloxacillin) or clindamycin. Herpetic whitlow may be treated with acyclovir. Laboratory The bacteriological diagnosis may be confirmed by Gram stain and culture on blood agar. The virological diagnosismay be confirmed by viral culture of vesicular fluid, direct fluorescent-antibody stainingof epithelial cellsfrom the baseof the lesion, or electron microscopy. Superficial Mycoses Cutaneousfungal infections involve the keratinized layer of the stratum corneum, hair, or nails. They may be caused by dermatophytes, Candida species,or lipophilic yeasts. In general, dermatophytic skin infections due to Epidermophyton jloccosum or Trichophyton or Mjcrosporum speciesproduce pruritic, scaly, erythematous lesions often with a characteristic “ringworm” appearance.Treatment with topical antifungal medications (e.g., tolnaftate and imidazole derivatives) is usually adequate. Candida albicans may colonize or infect skin or mucous membranes, especially if there is cutaneous maceration or altered host defenses ( g immunosuppressionand diabetes melliusi. Superficial yeast infection, usually caused by Candida species,tends to occur in the groin, diaper, or inframammary areas. The affected skin is raw, moist, and erythematous, with small satellite papulesor pustules.

TISSUE INFECTIONS

5

Tinea (pityriasis) versicolor is an infection of the stratum corneum due to the lipophilic yeast Malassezia furfur. Typical lesions, especially involving the torso and upper limbs, are faintly erythematous or hypopigmented maculeswith a fine scale. Treatment is with 2.5% selenium sulfide (Selsunshampoo). Laboratory If cutaneous fungal infection is suspected, the lesion should be cleaned and scrapings from the active border of the lesion should be obtained. The scrapings should be suspended in potassium hydroxide and examined microscopically for the presence of hyphae. Dermatophytes produce septate hyphae with arthrospores, while M. furfur produces short hyphae with blastospores. If there is nail involvement, scrapingsof debris or material beneath the nail plate are appropriate. Scalp lesions should be scraped with a scalpel blade to obtain fragments of hair for examination. Scrapings may be cultured on Sabouraud dextrose medium with chloramphenicol and cycloheximide to determine the fungal species. Such specimens shouldbe handled as described previously (18). Wood’s light may reveal golden-yellow fluorescence of lesions of tinea versicolor or hair infection due to Microsporum species or Trichophyton schoenleinii, which fluoresce bright yellow-green. Similarly, Wood’s lamp may be used to select hair for examination. Erythrasma Erythrasma is a chronic, superficial bacterial skin infection of the stratum corneum, often mistaken for a dermatophyte infection. It is causedby the diphtheroid Corynebacterium minutissimum and presents with fine, scaly, reddish-brown maculesor plaques,especially in the toe webs or genitocrural areas.The rash may be asymptomatic or pruritic. Erythrasma should be treated with oral erythromycin. Laboratory Wood’s lamp examination of lesions is diagnostic, revealing a characteristic coral red fluorescence,which is due to porphyrin production by the organism. A Gram-stainedimprint of the skin surface or scalesshows many small pleomorphic gram-positive bacilli, coccobacilli, or filaments. A culture is rarely required to make the diagnosis,but the organism may be grown from skin scrapings in tissue culture medium containing fetal bovine serum(35). ULCERS AND NODULES The common organisms,syndromes, and laboratory methodsused to investigate ulcers and nodulesare listed in Table 2.

6

SIMOR ET AL.

CUMITECH

TABLE Diseases and syndromes

Sporotrichoid

lesion

Common

causative

2. Ulcers and nodules

organisms

S. schenckii, M. marinum, Nocardia species

Blastomycosis Cryptococcosis

B. derma titidis C. neoformans

Cutaneous diphtheria Anthrax Tularemia

C. diphtheriae B. anthracis F. tularensis

23

Laboratory

diagonostic

methods

Histology (PAS and GMS stains”), Gram stain, acid-fast stain, biopsy culture on mycobacterial medium (e.g., 7H9 at 30 to 32”C), blood agar (sealed with Parafilm) for 4 weeks, Sabouraud dextrose with chloramphenicol and cycloheximide Culture on blood agar and Sabouraud dextrose with chloramphenicol and cycloheximide, India ink stain for C. neoformans Gram stain Culture on blood agar and tellurite blood agar Serum agglutinating antibody (fourfold rise in titer over 2 weeks or single titer of ~1: 160 after 2 weeks of illness)

“PAS, Periodic acid-Schiff; GMS, Gomori-methenamine-silver.

In cutaneousulcers there usually is a loss of epidermaland part of the dermal tissue (Fig. 5). Nodulesare inflammatory foci in which the most superficial cutaneouslayers are intact. A variety of bacteria and fungi causeulcerative or nodular skin lesionsor both following direct inoculation. Important examples include Corynebacterium diphtheriae, Bacillus anthracis, Francisella tularensis,Nocardia species,Mycobacterium marinum, and Sporothrix schenckii. Alternatively, cutaneous infection may follow hematogenous disseminationto the skin from someother focus of infection. For example, Blastomyces dermatitidis and Cryptococcus neoformanscause primary pulmonary infections which may be complicated by hematogenousdisseminationto extrapulmonary sites, such as the skin and soft tissues,in 10 to 70% of cases.Microscopy and culture are the main methods of laboratory diagnosis. However, serological testing is availablefor certain organisms,including somefungi. These are usually carried out in reference laboratories and are not described in detail in this Cumitech.

M. marinum is a pathogen of both fresh- and saltwater fish, and human infection usually follows superficial cutaneous injury in marine or tidal water, swimming pools, or tropical fish tanks. Although cutaneousinfection due to Nocardia asteroidesis usually a result of hematogenousdisseminationfrom a primary pulmonary focus of infection, primary cutaneous nocardiosis due to Nocardia brasiliensis or Nocardia caviae may occur following local trauma with inoculation of the organism.This may present as cellulitis, pyoderma, abscesses,or lymphocutaneoussporotrichoid lesions. The treatment of cutaneoussporotrichosis is with oral potassium iodide. M. marinum often respondsto rifampin and ethambutol or minocycline. Nocardiosis is conveniently and effectively treated with sulfamethoxazole-trimethoprim. The diagnosisof ulceronodular infections of the skin requires a careful epidemiological, occupational, and avocational history. For example, blastomycosisis endemicin North America along the Mississippi and Ohio river basins, along the St. Lawrence river valley, and in the statesand provinces bordering the Great Lakes. Cutaneousdiseaseis the most common extrapulmonary manifestation of blastomycosis, occurring with or without concurrent active pul-

Sporotrichoid Lesions Sporotrichoid lesionsare a distinctive form of ulceronodular infection with lymphatic involvement. Although classically associatedwith infection due to S. schenckii, lesionsmay also be seenwith infection due to M. marinum or Nocardia species. These lymphocutaneous infections begin with an ulcerated nodular lesion at the site of inoculation primarily on the extremities, followed by the development of subcutaneous nodules with overlying erythema and occasional ulceration proximally along lymphatics. Infection caused by S. schenckii, a dimorphic soil and plant fungus, often follows contact with thorny plants or sphagnummoss, with direct FIG. 5. Skin ulcer-loss inoculation of sporesinto subcutaneoustissue. layers.

of epidermal and dermal

CUMITECH

SKIN AND SUBCUTANEOUS

23

monary disease in 40 to 80% of cases. Infection due to S. schenckiior Nocardia speciesis most often associatedwith traumatic inoculation from a soil or plant source, whereas M. marinum infection is associatedwith swimmingpool or aquarium contact. Anthrax and tularemia are zoonoses, and a history of contact with the appropriate animalvector should be sought. Preexistingcutaneousulcers may alsobecome secondarily infected. Ischemic, diabetic, and decubitus ulcers are often colonized and occasionally infected with a variety of bacteria. Infection may become apparent with purulent drainage, surroundinginflammation, underlying abscesses,osteomyelitis, or bacteremia. Infections are typically mixed with aerobic gramnegativebacilli, streptococcalspecies,andanaerobes. Laboratory Unfortunately, there is often a poor correlation between organismsisolatedfrom superficial ulcer swabs compared with those recovered from deep tissue (33, 34). Therefore, the most reliable specimensare obtained by curettage of the base of the ulcer following the removal of overlying debris or by surgical biopsy of deep tissueswithout contact with superficiallayers of the ulcer (32, 33). In general, exudate from an ulcer or biopsy of a nodular lesion should be routinely examined by Gram stain and cultured aerobically on blood agar and MacConkey agar. Sabourauddextrose medium and Sabouraudmedium supplemented with chloramphenicol and cycloheximide may be usedif fungal infection is consideredlikely. If diphtheria is suspected,tellurite blood agar may alsobe used. The sporotrichoid lesions produced by S. schenckii, M. marinum, and Nocardia species are clinically indistinguishable.The etiological diagnosisis made by histological examination and culture of purulent exudate, aspirate, or biopsy of skin lesions. Histologically, stainable organismsmay be sparsely distributed, but if infection is due to Nocardia species, a Gram stainmay reveal branching, gram-positivebacilli TABLE Diseases and syndromes

Common

SINUS TRACTS The causativeorganismsand laboratory methods associatedwith infections in which a sinus tract developsare listed in Table 3. A sinustract is a communication between an infected deep tissue or abscessthrough subcutaneoustissue andopeningonto the skin surface(Fig. 6). These arisefrom deepinfections suchasosteomyelitis,

3. Sinus tracts

causative organisms

Actinomyces

Madura foot

Petriellidium boydii, Madurella myce toma tis, Phialophora verrucosa Mycobacterium tuberculosis

Miscellaneous deep or chronic foci of infection

s. aureus,

7

characteristic of actinomycetes. Nocardia species are weakly acid-fast. In sporotrichosis, organismsare infrequently seen,but occasionally round, oval, or cigar-shapedyeast cells, 3 to 8 pm in size, may be seen with periodic acidSchiff or Gomori-methanamine-silverstain. If there is a history of swimmingpool or aquarium contact, a Ziehl-Neelsenor fluorochrome stain for mycobacteria should be done. The skin lesion aspirateor biopsy should be cultured aerobically on blood agar at 35 to 37°C and on Sabourauddextrose medium at room temperature. These mediawill support the growth of S. schenckii and Nocardia species,but as growth of these organismsis slow (2 to 7 days), the plates shouldbe kept for at least 4 weeksbefore beingdiscardedas negative. Sabouraudmedium supplementedwith chloramphenicol and cycloheximide may also be used to reduce contamination with commensalflora but may not support the growth of Nocardia species.Nocardia speciesmay also be grown on mycobacterial culture media. Biopsy specimensfor the recovery of M. marinum should be homogenizedor ground in sterile saline and inoculated directly (without decontamination) onto routine media for the isolation of mycobacteria, incubated at 30to 32 and 35 to 37°C (38). Also broth, suchas Middlebrook 7H9 or 7H12, which is used in Bactec 460 (Johnston Laboratories), may be usedas long as it is incubated at 30 and 35°C. The diagnosisof tularemia is best made by detecting a fourfold rise in antibody titer during a 2- to 3-week period of illness or by noting a titer of 2 1:160after a 2-week illness.No attempt shouldbe madeto isolatethe organismexcept in specialized laboratories in view of the risk of laboratory-acquired infection in the staff.

Actinomycosis

Tuberculosis

TISSUE INFECTIONS

species

Enterobacteriaceae, Pseudomonas spp.

Laboratory

diagnostic

methods

Gram stain, anaerobic culture in blood agar and in a broth for 1 to 2 weeks KOH, culture on Sabouraud with and without chloramphenicol and cycloheximide Fluorochrome, Ziehl-Neelsen smear, culture on Lowenstein-Jensen medium Gram stain, culture aspirate or deep tissue on blood agar, MacConkey agar

8

SIMOR ET AL.

CUMITECH

Epidermis

Dermis

Subcutaneous fat

3 Fascia

1 MUSCl9

Osteomyelitis

-

Bone

FIG. 6. Sinus tract from chronic osteomyelitis.

pyomyositis, lymphadenitis, or in&a-abdominal abscesses.In many instances the infection is polymicrobial and the organismscolonizing the cutaneousportions of the tract may be different from those deep in the tissues. For this reason cultures taken from the cutaneous exit of the sinustract may be misleading. Several specific organismsare characterized by soft tissue infections with sinus tracts. S. aureusproduces deepabscessesand carbuncles discharging thick pus. Cervical lymphadenitis from mycobacteria, especially tuberculosis in the neck, may produce the chronic draining sinusesknown asscrofula. Actinomycosis, classically defined as lumpy jaw, is an extremely painful hard swellingaround the angleof the jaw that spontaneously drains watery secretions containing “sulfur granules.” These yellow granules are composedof microbial clumps. If left untreated, actinomycosis progressesto a chronic draining sinus. The source of the organismis the patient’s oral cavity, and poor dental hygiene may be an etiological factor. Madura foot occurs when soil organisms,suchasNocardia speciesand various fungi (e.g., Petriellidium boydii, Madurella mycetomatis, and Phialophora verrucosa), are inoculated into the soft tissuesof the foot to produce multiple abscesses with sinustracts and sometimesosteomyelitis.

23

Culture procedures should be the sameas those for a surgical wound (seebelow) and should be designedto recover both facultative and anaerobic bacteria. Granules found in casesof mycetoma should be cultured. The lack of reliability of culturing superficialdrainagematerial will justify a surgical procedure to obtain a good specimen in those circumstanceswhere the severity demandsan accurate microbiological diagnosis. BURN CULTURES Burn injuries may be classified according to the responsible agent, such as flame, scald, chemical, and electrical. Although this may be important in recognizing and managingthe complications associatedwith each type, the major concerns are the total area and depth of the burn. The depth is used to distinguish among first-, second-, and third-degree burns. Firstdegree burns are superficial and require little treatment. Second-degreeburns may show blistering and loss of surface epithelium but eventually heal without scarring or grafting. A thirddegree burn is a full-thickness skin injury and resultsin permanentlossof the skin and replacement with scar tissueunlessgrafted. The severity of the burn is expressed as the estimated percentageof the body surface that has suffered second- and third-degree burns. When the second- and third-degree burns total greater than 10%of the body surface in children and 15% of the body surface in adults, the patient is admitted to a hospital. Other factors such as smoke inhalation and the site of the burn may result in admissionof patients with lesserareasburned. The greatest danger to the patient during the initial therapy is fluid and electrolyte imbalance due to excessive lossthrough the burned tissue. Modem therapy has greatly increased the survival of patients during this stage, and sepsisis now the most common cause of death. Historically, hemolytic streptococci and staphylococci were the commonest organisms encountered (23). With the advent of potent antimicrobial agents, these are more readily prevented or controlled, and methicillin-resistant S. aureus, the gram-negative bacilli, notably P. aeruginosa, and yeasts such as C. albicans or filamentous fungi such as Fusarium sp. have become the predominant organisms (23). Attempts to prevent infections have included systemic and topical antimicrobial agentsaswell asprotective isolation techniques. Early removal of eschar (burned tissue)and grafting also help to prevent infection while reducing the complications associated with scarring.

Laboratory The culture of sinustracts is extremely dif& cult in that reliable specimensare difficult to obtain. There is a poor correlation between the results of culture of superficial material and that obtainedfrom deeperinfected tissues.If surgical exploration is performed, then culture shouldbe taken from the deepestportion of the sinustract possible.If generalized symptomssuch as fever and chills are present, then blood cultures may reveal the more significantorganisms.Occasion- Laboratory ally a deep abscessor portion of the tract can be Many studiesduring the 1960sdeveloped the aspirated, allowing for a more reliable specimen. following concept of the sequenceof events in

CUMITECH

23

SKIN AND SUBCUTANEOUS

burn sepsis(3, 5, 8, 13, 20, 22, 39). The surface of the burn contains deadtissueand protein-rich fluid from the patient. Organismsfrom the patient or the environment colonize this surface. Growth on the surface continues until a heavy microbial load is present. When a large enough concentration is present, extension into the underlying tissuesoccurs and generalizedinfection with bacteremiaensues.The studiessuggestthat the occurrence of invasion with complications is associatedwith bacterial counts of ~10~ CFUlg of tissue. This led to the development of quantitative methods, both smearsand cultures, for assessingsurgically removed biopsiesof burns. It has been demonstrated that surface cultures alone are inadequateand often misleading.Consequently, the culture of deeper tissuesis used in many laboratories, a procedure that is also controversial becauseof difficulty in interpretation. Although biopsies have been widely used, certain inadequacieshave been noted. Burns are not evenly colonized and the selectionof the site of biopsy is important. Lists of factors to be consideredin choosing a biopsy site have been publishedto guide surgeons(28). Marked variations within the biopsy itself have also been documented by Woolfrey et al. (43), who divided biopsiesin half and treated each part as a separate biopsy. Correlation between the two halves is poor, suggesting marked variations within the tissue. Another major concern is the inability to estimatethe depth of microbial invasion into the tissue regardless of the method used. This has led to a variety of techniquesto estimate the depth to which organisms have spread. These methods have included a variety of histopathological and culture techniques. (i) Quantitative smear and culture. Quantitative smearand culture are performed on a surgically excised biopsy of the burn. While it is desirableto obtain a generousportion of tissue, such as0.5 g, usually one hasto accept a smaller amount. An area suggestiveof infection is chosen, and a portion of the tissue down to and including viable bleeding tissue is removed and submitted to the laboratory in a sterile container. In the laboratory the biopsy is weighed, utilizing a scale with an accuracy of +O.OOlg. The tissue is then homogenized with either a hand grinder or an electric homogenizer in a measuredamount of broth or saline. The resulting homogenateis further diluted to produce a range of 10-l to 10B5(wt/vol) dilutions. With either a loop or a pipette measuredvolumes are then placed on a variety of agar plates, usually including sheep blood agar and MacConkey agar. Anaerobic cultures are not routinely done by most laboratories as anaerobic infections are uncommon complications. Identification and

TISSUE INFECTIONS

9

susceptibility testing are performed on the isolates, and the quantitative value of each isolate is calculated from the weight of the biopsy and the dilution. Example: Biopsy weight and dilution = 0.2 g of tissue homogenizedin 2 ml of broth (a) l:lO, l:lOO, 1:1,0(H)dilutions made Homogenate; all dilutions plated, using a O.OOl-mlquantitative loop (b) ResultHomogenate = >lOO colonies of Escherichia coli 1:lO dilution (c) = ~80 colonies of E. coli 1:100dilution = 1 colony of E. coli 1:1,000dilution = no growth Calculation colony count x dilution (a x b x c)/weight of biopsy (g) = CFU/g of tissue (80 x [lo (a) x 1,000(b) X 10(c)1)/0.2 g = 4 x 10’ CFU/g of tissue Methods for testing susceptibility to topical agents have been developed but are not routinely used as they lack standardization and the clinical significanceremainsuncertain. Quantitative smearsmay also be prepared at the sametime by the method reported by Magee et al. (24). A measuredamount of homogenateis spread evenly over a l-cm2 area of a slide and allowed to dry. A Gram srain is performed, and 10fields are examinedwith a 100x oil immersion lens. A seriesof calculations allows the determination of the bacterial counts in terms of organismsper gram of tissue. (ii) Histopathologicaltechniques. Histopathological techniques have been used to detect fungal infection and in an attempt to determine the location of organismsin burned tissue. The standardsurgicalpathology techniquesof frozen section and quick section have been applied. However, technical problems may be encountered in obtaining good sections, especially when the frozen section method is used. The biopsiesare usually graded by the classification of Pruitt and Foley (29). In this classification the gradesextend from grade 1 (surface organisms only) to grade 6 (invasion of viable tissue). The histopathological methods have a number of disadvantages.The amount of tissue examined is very small, being limited to a few thin slices taken from the biopsy. Recognition of organisms in tissue sections is more difficult than smears and dependson the quality of the slide, stains used, and experience of the microscopist. The concentration of bacteria required to allow de-

10

SIMOR ET AL.

CUMITECH

TABLE Diseases and syndromes

Common

causative

23

4. Wound infections organisms

Simple postoperative wound infection

S. aureus, S. epidermidis, group A streptococci, Enterobacteriaceae, Enterococcus spp., Bacteroides spp., Clos tridium spp.

Complicated wound infection

Group A streptococci, S. aureus, Enterobacteriaceae, Pseudomonas spp., A. hydrophila, V. vulnljkus, Bacteroides spp., Clostridium spp., anaerobic cocci, microaerophilic cocci, Fusobacterium spp.

tection has not been determined although experience has shown that organisms are readily detected in biopsieswith lo5 CFU or more per g of tissue when quantitative counts have been performed on the samebiopsy specimen.Histopathological methods require simultaneousculture to provide the identification and antimicrobial susceptibilitiesof the organisms.Although the correlation between the methods is usually good, some cases will demonstrate discrepancies between histology and microbiological assessment, making the correlation difficult or unreliable. (iii) Miscellaneousculture methods. Surface culture techniques have been investigated with swabs, contact plates, and contact sponges. However, these are not recommendedbecause they give no estimationof penetration and fail to correlate with clinical experience. Levine et al. (22) reported a simple quantitative swab culture technique involving traumatizing the burn surface with the swab and placing it in transport mediumfor quantitative culture. Neal et al. (27) cultured frozen section slicesof burn biopsieson agar. By observing the location of colonies in relationship to the tissuestructures, an estimate of invasiveness can be made and graded. The gradesrangedfrom stageI (no growth in 16h) to stage III (full-thickness growth). Recently a technique consisting of an impressionor touch preparation of the deep aspect of a burn biopsy and a swabculture from the depthsof the biopsy site has been described (2). In practice this has proved as useful as and less expensive than quantitative smear and culture. All of these culture techniqueshave been describedasuseful and valuable. At present no commonly accepted standardmethod exists. Quantitative smearand culture have been the most commonly used techniques in the past. Somebum centers have acceptedother methods becausethey believed them to be superior to smearand culture. To be useful, methods must cause a minimum of patient discomfort, give rapid results, be inexpensive and accurate, esti-

Laboratory

diagnostic

methods

Gram stain; culture of pus, aspirate, or tissue on blood agar and MacConkey aerobically; anaerobic methods as in Cumitech 5 ; Trypticase soy broth Gram stain; aerobic, microaerophilic, and anaerobic culture of pus or tissue (see Cumitech 5)

mate the depth of invasion, allow the identification and antimicrobial susceptibility testing of the organisms, and correlate well with clinical findings. None of the present techniques satisfy all of these requirements. SIMPLE POSTOPERATIVE WOUND INFECTIONS The organisms associated with simple and complicated wound infections are listed in Table 4. Infection in a surgicalwound occurs when the wound, usually in the intraoperative or immediate postoperative period, is contaminated by microorganisms.The sources of the organisms may include colonized body sitesof the patients, such as the nose, oral cavity, female genital tract, alimentary tract, and skin (25). The medical and nursing stti may also be a source of organisms,as may the inanimate hospital environment. Host factors that may contribute to the pathogenesisof a surgical wound infection include obesity, diabetes, vascular insufficiency, and immune suppression.Microbial factors include microbial load and “virulence” of the organism. Surgical factors, such as the duration of an operation, poor hemostasis,the presence of a foreign body, and devitalized tissue, may contribute to the likelihood of infection. In the presenceof these risk factors the inoculum size necessary to initiate infection is much smaller than that required to cause infection in the healthy tissue (9). Infection rates vary from one type of surgical procedure to another. Surgical procedures may be classifiedas clean, clean-contaminated, contaminated, and dirty (6, 7). Implicit in this classification is the risk of postoperative infection. Additionally, infections of a remote site, for example, a urinary tract infection, place the surgicalpatient at a higher risk of postoperative infection. Overall, infection rates in modern practice rangefrom 1 to 5%. The principal pathogensare S. aureus, Staphylococcus epidermidis, E. coli, Klebsiella spp., Enterobacter spp., Pseudomonas spp., Enterococcus spp., Bacteroides

CUMITECH

23

SKIN AND SUBCUTANEOUS

spp., and Clostridium spp. Some wounds that appear infected may not yield a pathogen on culture while others will grow multiple species. Superficial wound infections often start at a suture and may be painful, tender, red, and swollen. Pus may exude, particularly if one or more sutures are removed to allow free drainage. Malodorous discharge may suggest the presenceof anaerobic bacteria. Mycobacterium chelonei and Mycobacterium fortuitum’ may causeinfection, complicating cardiac surgery, mammoplasty, and ocular and other clean surgery (41). These organismsmay produce chronic disfiguring disease. Antimicrobial managementmust be tailored to the bacteriological diagnosis. Empiric therapy will usually include broad-spectrumagentswith activity againstgram-positive cocci (e.g., a firstgeneration cephalosporin), as well as one with activity againstgram-negativebacteria (e.g., an aminoglycoside). If anaerobes are suspected, one may choose clindamycin, cefoxitin, or metronidazole, all effective against Bacteroides spp., the common pathogens.Penicillin G is the drug of choice against Clostridium perfringens.

TISSUE INFECTIONS

11

ered as potential pathogens and antimicrobial susceptibility tests should be carried out. Conversely, low numbers of coagulase-negative staphylococci associatedwith enteric flora in an infected colon resection wound could be disregarded to the extent that susceptibility testing need not be performed. The reason for this is that they do not constitute a clinical problem and will disappear when the other pathogens are eliminated.

COMPLICATED WOUND INFECTIONS Complicated infections of the skin and subjacent structures may occur following surgery or trauma. Classification of these infections is difficult due to overlapping of affected anatomical sites, causative organisms,and clinical manifestation. Many of these infections are severe, rapidly progressive, and associatedwith a high mortality rate. Infectious gangreneis a rare diseasein which bullous necrosisof the skin may be associated with bacteremia and metastatic lesions. This diseaseis often fatal. Synergistic gangrene (Fig. 7), sometimesreferred to as Meleney’s gangrene, usually comLaboratory plicates surgery of the alimentary tract. It starts A volume of aspirated pus or a swab heavily as an ulcer near the wound and can spread to impregnatedwith pus may be examined micro- affect much of the anterior abdominal wall. biologically. A Gram-stained smear may give Gas gangrene is usually associated with C. someindication of the variety of infecting flora. perfringens, an organism that may colonize a Some laboratories make it a practice to culture wound without causing disease, may cause a exudates from superficial wounds for aerobic spreadingcellulitis, or may extend into muscle and facultative organisms on blood agar and to causemyonecrosis.It may be associatedwith MacConkey agar, as well as to prepare a broth a thin watery discharge rather than a purulent culture. Culture of superficial wounds for anae- exudate. A similar syndrome of musclenecrosis robes in the absenceof a clinical indication is may be caused by Aeromonas hydrophila and expensive and unrewarding. Pus from deep Vibrio vulnijkus, and cellulitis may be causedby wounds or from wounds showinggasbubblesor Vibrio species,Klebsiella spp., E. coli, and/or foul-smelling discharge should be cultured for nonclostridial anaerobes such as Bacteroides anaerobes as well as aerobic and facultative spp. and cocci. bacteria. Details of specimen collection and Necrotizing fasciitis (Fig. 8) usually starts at processingfor anaerobesare presentedin Cumian abdominal surgicalwound and spreadslatertech 5 (11). ally to the flanks, up to the nipple line, and down M. chelonei and M. fortuitum, although to the inguinal region. The patient is usually very classedas rapid-growing mycobacteria capable ill. The overlying skin appearsnormal early in of growth on samplemedia, usually require 1 to the illness, turning reddish-blue as the disease 6 weeks to grow on primary culture. In routine diagnostic laboratories such infections may be missed,unlessone is aware of their possiblerole and cultures are saved. These organisms,especially M. chelonei, may be misidentifiedasdiphtheroids in a broth culture unless an acid-fast stain is performed. When isolates from infected wounds are reported, it is essentialto take into account the source of the specimen. Thus, all coagulasenegative staphylococcal isolates from infected sternotomy wounds or associatedwith vascular or implant orthopedic surgery shouldbe considFIG. 7. Progressive bacterial synergistic gangrene.

12

SIMOR

ET AL.

CUMITECH

23

Other antimicrobial agents directed at facultative and aerobic bacteria may include imipenem, ceftazidime, ciprofloxacin, - and combinations containing beta-lactamaseinhibitors such asclavulanic acid and sulbactam. Antimicrobial therapy directed againstanaerobesis essential.This may include metronidazole, clindamycin, piperacillin , and cefoxitin. FIG. 8. Necrotizing

fasciitis .

progresses.Bus may drain through the skin in the flanks or in other parts remote from the original wound. Foumier’s disease(Fig. 9) is a form of necrotizing fasciitis affecting the perineum and scrotum in which the superficial layers of the skin blacken and sloughoff. Anaerobic bacteria such as Bacteroides spp., Fusobacterium spp., Clostridium spp., and gram-positive cocci, as well as facultative bacteria such as membersof the Enterobacteriaceae, staphylococci, and enterococci, may be involved. Microaerophilic streptococci are often seen in synergistic gangrene, often in associationwith S. aureusand members of the Enterobacteriaceae. Some clinicians (lumpers rather than splitters) like to reduce these myriad descriptions to three syndromes: (i) crepitant cellulitis, which may be clostridial or nonclostridial; (ii) necrotizing fasciitis, including Meleney’s gangreneand Foumier’s disease; and (iii) gasgangrenewith myonecrosis. Infection may become complicated and extend to the musclesof the leg when the arterial supply is compromised,as in diabetesmellitus. There may be extensive myonecrosiscausedby anaerobessuch as Clostridium spp., anaerobic cocci, and Bacteroides spp. in the area of vascular insufficiency. Facultative flora may alsobe present, including Proteus spp. The treatment of these infections is surgical with adjunctive antimicrobial therapy (17, 26, 37). Since the large majority involve a mixed infecting flora, including facultative anaerobes and anaerobes,a broad-spectrum antimicrobial therapy is indicated. This may consist of an aminoglycoside with clindamycin or a betalactam effective against gram-positive cocci.

FIG. 9. Fournier’s gangrene.

Laboratory The bacteria commonly isolated from wound infections include S. aureus, group A streptococci, anaerobic cocci, Clostridium spp., especially C. perfringens, members of the Enterobacteriaceae, Bacteroides spp., and Fusobacterium spp. Effective laboratory investigation requires the collection of a volume (up to 5 ml) of aspirated pus or excised tissue. Fluid specimensmay be transported in anaerobic transport tubes or vials, anaerobic biobags, or if these are unavailable, plugged syringes or gassedout tubes. Tissuesamplesmay be sent to the laboratory in dry sterile test tubes or in gassedout tubes. Gram-stainedsmearsmay indicate the variety of microorganismsassociated with the lesion, and presumptive therapy can be guided by the Gram stain results. This is particularly the case with C. perfringens myonecrosis, which may be rapidly progressive and which may be recognized on the basisof brick-shaped gram-positive rods. Note that on Gram-stained smearsthese may decolorize readily and someorganismsappear gram negative. There are few pus cells in C. perfiingens infection. Specimensshould be cultured on blood agar and on a selective medium such as MacConkey agar. The common facultative and aerobic flora will appear within 24 h. The microbiological examination of all of these infections requires culturing for anaerobes(11)) as well as aerobesand facultative anaerobes. INFECTIONS COMPLICATING BITES Both human and animal bite wounds may be contaminated with oral flora, as may those causedby trauma related to the mouth, such as fist injuries from striking teeth, and those associated with dental injuries or procedures (Table 5). Bite-associated infections vary according to the depth of the bite, the dental pattern of the mouth, and the oral flora present. They alsovary to some degree with the site of the injury as infection tends to spread along fascial planes. Human bites or fist injuries are always contaminated with oral flora and tend to cause severe necrotizing infections unless treated aggressively. Dog and cat bites are often deeppuncture wounds and are sometimesinfected by organismsabsentor infrequent in human bites. Her-

CUMITECH

SKIN AND SUBCUTANEOUS

23

TABLE Diseases and syndromes

Common

Animal bites

P. multocida, DF-2, S. moniliformis, S. minor Unknown Normal oral flora

Cat scratch disease Human bites

causative

Laboratory Cultures of fresh animal bites are not warranted as they yield no useful clinical information. The best material for culture is usually pus aspirated from the depths of the wound or cultures taken during the time of incision and drainage or debridementof the infected wound. Both aerobic and anaerobic cultures should be performed with a variety of media to help separate the anticipated mixture of organisms.

13

5. Bites

organisms

bivorous animalssuch as horsesand cows have a bite that includesa grinding action, resulting in severe tissue maceration. Rabies and tetanus are infectious complications of bites but are not investigated by wound culture. Culture of the fresh bite is not rewarding and simply reflects the oral flora of the biter. Cultures of infections resulting from bites nearly always yield a mixture of organisms,including anaerobes.A common isolate from animal bites is Pasteurella multocida. This is part of the oral flora of cats and dogs, as well as other animals ranging from rabbits to lions. Bacteremia arising from animal bites may yield unusual isolates. Bacteremia with the organism DF-2 (dysgonic fermenter type 2) has been associatedwith dog and cat bites (1,4, 36). Bacteremia as part of rat bite fever causedby either Streptobacillus moniliformis or Spirillum minor is associatedwith rodent bites. The latter organismis difficult to culture, requiring animal inoculation to detect the bacteremia. Another unusualinfection associated with pet bites and cat scratches is cat scratch disease. Infection at the site of initial injury is followed by the enlargementof the local lymph nodesas evidence of a suppurative lymphadenitis. Gram-negative bacilli have been demonstrated in tissue sections of the lymph nodes, and a recent report suggeststhat vegetative bacteria have been isolated in artificial culture media-biphasic brain heart infusion agar and broth (10). The important principles in treating bites of any type are adequatedebridement of dead tissue and adequatedrainageby leaving the wound open. Prophylactic antibiotics are recommendedas these wounds are always contaminated.

TISSUE INFECTIONS

Laboratory

diagnostic

methods

Gram stain; blood agar; MacConkey agar; blood culture Histology Gram stain; culture aerobically on blood agar, chocolate agar, and MacConkey agar; culture anaerobically as described in Cumitech 5

LITERATURE

CITED

1. Bobo, R. A., and E. J. Newton. 1976. A previously undescribed gram-negative bacillus causing septicemia and meningitis. Am. J. Clin. Pathol. 65:X4-569. 2. Boyle J., F. J. Roberts, C. F. T. Snelling, L. Boileau, and B. Gelfant. 1985. Rapid, simple, and inexpensive method to rule out bacterial invasion of fat subjacent to fullthickness burn eschar. J. Burn Care Rehabil. 6:402-407. 3. Brentano, L., and D. L. Gravens. 1967. A method for the quantitation of bacteria in burn wounds. Appl. Microbial. 15670-67 1. 4. Carpenter, P. D., B. T. Heppner, and J. W. Gnann, Jr. 1987. DF-2 bacteremia following cat bites. Am. J. Med. 82:621-623. 5. Clarkson, J. G., C. G. Ward, and H. C. Polk. 1%7. Quantitative bacteriologic study of the bum wound surface. Surg. Forum 18:506-507. 6. Cruse, P. J. E. 1970. Surgical wound sepsis. Can. Med. Assoc. J. 102:25 l-258. 7. Cruse, P. J. E. 1973. A five-year prospective study of 23,649 surgical wounds. Arch. Surg. 107:206-210. 8. Eade, G. G. 1958. The relationship between granulation tissue, bacteria, and skin grafts in burned patients. Plast. Reconstr. Surg. 22:42-55. 9. Elek, S. D., and P. E. Conen. 1957. The virulence of Staphylococcus pyogenes for man. A study of the problems of wound infection. Br. J. Exp. Pathol. 38:573-586. 10. English, C. K., D. J. Wear, A. M. Margileth, C. R. Lissner, and G. P. Walsh. 1988. Cat-scratch disease. Isolation and culture of the bacterial agent. J. Am. Med. Assoc. 259: 1347-1352. 11. Finegold, S. M., W. E. Shepherd, and E. H. Spaulding. 1977. Cumitech 5, Practical anaerobic bacteriology. Coordinating ed., W. E. Shepherd. American Society for Microbiology, Washington, D.C. 12. Fleisher, G., S. Ludwig, and J. Campos. 1980. Cellulitis: bacterial etiology, clinical features and laboratory findings. J. Pediatr. M:591-593. 13. Georgiade, N., M. Lucas, and R. Georgiade. 1%7. The use of a new potent topical antibacterial agent for the control of infection in the bum wound. Plast. Reconstr. Surg. 39: 349-356. 14. Ginsberg, M. B. 1981. Cellulitis: analysis of 101 cases and review of the literature. South. Med. J. 74:530-533. 15. Goldgeier, M. H. 1983. The microbial evaluation of acute cellulitis. Cutis 31:649-656. 16. Gustafson, T. L., J. D. Band, R. H. Hutcheson, Jr., and W. Schaffner. 1983. Pseudomonas folliculitis: an outbreak and review. Rev. Infect. Dis. U-8. 17. Haldane, E. V., and C. E. van Rooyen. 1972. Treatment of severe Bacteroides infections with parenteral clindamytin. Can. Med. Assoc. J. 107:1177-l 181. 18. Haley, L. D., J. Trandel, and M. B. Coyle. 1980. Cumitech 11, Practical methods for culture and identification of fungi in the clinical microbiology laboratory. Coordinating ed., J. C. Sherris. American Society for Microbiology, Washington, D.C. 19. Hook, E. W., III, T. M. Hooton, C. A. Horton, M. B. Coyle, P. G. Ramsey, and M. Turck. 1986. Microbiologic

14

20 21 22

23 24.

25. 26. 27.

28.

29. 30.

31. 32.

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evaluation of cutaneous cellulitis in adults. Arch. Intern. Med. U&295-297. Lawrence, J. C., and Ii. A. Lilly. 1972. A quantitative method for investigating the bacteriology of skin: its application to bums. Br. J. Exp. Pathol. 53:550-558. Lee, P. -C., J. Tumidge, and P. J. McDonald. 1985. Fineneedle aspiration biopsy in diagnosis of soft tissue infections. J. Clin. Microbial. 22:80-83. Levine, N. S., R. B. Lmdberg, A. D. Mason, and B. A. Pruitt. 1976. The quantitative swab culture and smear: a quick simple method for determining the number of viable aerobic bacteria on open wounds. J. Trauma 16:89-94. Luterman, A., C. C. Dasco, and P. W. Curreri. 1986. Infections in bum patients. Am. J. Med. Bl(Suppl. 1A): 45-52. Magee, C., B. Haury, G. Rodeheaver, J. Fox, M. T. Edgerton, and R. F. EdIich. 1977. A rapid technique for quantitating wound bacterial count. Am. J. Surg. 133:760762. Meleney, F. L. 1935. Infection in clean operative wounds: a nine year study. Surg. Gynecol. Obstet. 60:264-276. MuIIick, R. N., and N. P. Zissis. 1986. Piperacillin vs gentamicin-clindamycin combination in in&a-abdominal infections. Curr. Ther. Res. Clin. Exp. 41:536-541. Ned, G. D., G. R. Lindhohn, M. J. Lee, J. A. Marvin, and D. M. Heimbach. 1981. Bum wound histologic culture-a new technique for predicting bum wound sepsis. J. Bum Care Rehabil. 2:35-39. Pruitt, B. A. 1982. Bums and soft tissues, p. 113-131. In H. C. Polk, Jr. (ed.), Clinical surgery international, ~014. Infection and the surgical patient. Churchill Livingstone, Ltd., New York. Pruitt, B. A., Jr., and F. D. Foley. 1973. The use of biopsies in bum patient care. Surgery 73:887-897. Ratnam, S., K. Hogan, S. B. March, and R. W. Butler. 1986. Whirlpool-associated folliculitis caused by Pseudomonas aeruginosa: report of an outbreak and review. J. Clin. Microbial. 23:655-659. Rudoy, R. C., and G. Nakashima. 1979. Diagnostic value of needle aspiration in Haemophilus influenzae type b cellulitis. J. Pediatr. 94:924-925. Sapico, F. L., H. N. Canawati, J. L. Witte, J. Z. Montgomerie. F. W. Wagner. Jr.. and A. N. Bessman. 1980.

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39

40 41

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Quantitative aerobic and anaerobic bacteriology of infected diabetic feet. J. Clin. Microbial. 12:413-420. Sapico, F. L., V. J. Ginunas, M. Thornhill-Joynes, H. N. Canawati, D. A. Capen, N. E. Klein, S. Khawam, and J. Z. Montgomerie. 1986. Quantitative microbiology of pressure sores in different stages of healing. Diagn. Microbiol. Infect. Dis. 5:3 l-38. Sapico, F. L., J. L. Witte, II. N. Canawati, J. Z. Montgomerie, and A. N. Bessman. 1984. The infected foot of the diabetic patient: quantitative microbiology and analysis of clinical features. Rev. Infect. Dis. d(Supp1. l):S171-176. Sarkanyi, I., D. TapMn,.and H. Blank. 1961. The etiology and treatment of erythrasma. J. Invest. Dermatol. 37:283288. Smith, C., and S. J. Rubin. 1983. DF-2 septicemia. Clin. Microbial. Newsl. 5:90-91. Smith, J. A., A. G. Skidmore, A. D. Forward, A. M. Clarke, and E. Sutherland. 1980. Prospective, randomized, double-blind comparison of metronidazole and tobramycin with clindamycin and tobramycin in the treatment of intra-abdominal sepsis. Ann. Surg. 192:213-220. Sommers, H. M., and J. K. McClatchy. 1983. Cumitech 16, Laboratory diagnosis of the mycobacterioses. Coordinating ed., J. A. Morello. American Society for Microbiology, Washington, D.C. Teplitz, C., D. Davis, A. D. Mason, Jr., and J. A. Moncrief. 1964. Pseudomonas bum wound sepsis. I. Pathogenesis of experimental Pseudomonas bum wound sepsis. J. Surg. Res. 4:200-216. Uman, S. J., and C. M. Kumin. 1975. Needle aspiration in the diagnosis of soft tissue infections. Arch. Intern. Med. 135:959-961. Wallace, R. J., Jr., J. M. Swenson, V. A. Silcox, R. C. Good, J. A. Tschen, and M. S. Stone. 1983. Spectrum of disease due to rapidly growing mycobacteria. Rev. Infect. Dis. 5~657-679. Weaver, R. E. 1985. Erysipelothrix, p. 209-210. In E. H. Lennette, A. Balows, W. J. Hausler, Jr., and H. J. Shadomy (ed.), Manual of clinical microbiology, 4th ed. American Society for Microbiology, Washington, D.C. Woolfrey, B. F., J. M. Fox, and C. 0. Quail. 1980. An evaluation of bum wound quantitative microbiology. Am. J. Clin. Pathol. 75:532-537.