Microbiology in surgical practice: a free MRCS Part A question

This is Fournier's gangrene, a type I (polymicrobial) necrotising fasciitis of the perineum. It typically follows anorectal or urogenital sepsis or surgery in diabetic, obese or immunocompromised patients, and cultures grow a synergistic mixture of facultative Gram-negative bacilli (such as Escherichia coli), streptococci, enterococci and anaerobes such as Bacteroides; crepitus reflects gas from anaerobic metabolism. A pure group A streptococcal growth defines type II necrotising fasciitis, usually of a limb in a previously healthy person. Clostridial myonecrosis follows deep contaminated wounds and involves muscle rather than fascia. Vibrio vulnificus causes a marine-associated monomicrobial type III infection. MRSA alone is an uncommon cause. Reference: Bailey & Love 28e.