Microbiology

One ofthe characteristics ofFournier's gangrene is that it is a polymicrobial infection, with a mean of four different organisms usually cultured (Bahlmann et al. 1983; Baskin et al. 1990).

Aerobic, anaerobic, Gram-positive and Gram-negative bacteria, yeasts, and even mycobacteria can be found (Table 6.3). The most commonly cultured organ-

Table 6.3. Most common causative organisms

Gram-negative

E. coli

Klebsiella pneumoniae Pseudomonas aeruginosa Proteus mirabilis Enterobacteria

Gram-positive

Staphylococcus aureus Beta-hemolytic streptococci Streptococcus faecalis Staphylococcus epidermidis

Anaerobes

Bacteroides fragilis Peptococcus Fusobacterium Clostridium perfringens

Mycobacteria

Mycobacterium tuberculosis Yeasts

Candida albicans isms are Escherichia coli, Bacteroides, beta-hemolytic streptococci, Staphylococcus spp., and Proteus. Besides being found in the lumen of the gastrointestinal tract, these bacteria are also normal commensal flora of the skin folds and hair follicles of the perineum (Benizri et al. 1996; Smith et al. 1998). This mixed spectrum of bacteria acts in a synergistic fashion to produce and promote a fulminant necrotizing fasciitis.

Anaerobic organisms are responsible for the formation of subcutaneous gas, which leads to the characteristic crepitus often found on palpation. Clostridial infection, classically associated with gas formation, is not commonly encountered, but should be suspected when there is a colorectal origin (Spirnak et al. 1984; Baskin et al. 1990).

It is extremely important to obtain cultures in order to identify the causative organism(s), because this determines the correct choice of antibiotic treatment. Because of the difficulty of culturing anaerobic organisms, a subcutaneous aspirate should be obtained, and at initial debridement a piece of infected tissue should also be sent for anaerobic culture. Microbiological studies should include acid fast staining for Mycobacterium tuberculosis and culture for fungal infection.

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