This patient has necrotizing fasciitis caused by Vibrio vulnificus. Patients who are immunocompromised, particularly those with liver disease, are at increased risk for infection with this gram-negative bacillus. Infection usually occurs after consumption of raw shellfish (such as oysters) or skin trauma incurred in contaminated warm (>20 °C [68.0 °F]) sea water or brackish water where the organism thrives. Hemorrhagic bullae are the classic cutaneous manifestation. Guideline recommendations for the management of these infections include antibiotic therapy with doxycycline plus ceftazidime in addition to surgery.

Erysipelothrix rhusiopathiae is a gram-positive bacillus that can infect animals, including swine and poultry, and is a saprophyte associated with fish, crustaceans, and molluscs. Exposures to these types of animals or their secretions can be occupationally acquired (fisherman, fish and shellfish handlers, veterinarians, and butchers). Classically, a painful localized violaceous cutaneous infection of the hand or fingers (known as erysipeloid) develops at the site of trauma or a preexisting wound. Fever is not often present. More diffuse skin infections and systemic infections including bacteremia and endocarditis are well-described but are much less common.

Methicillin-resistant S. aureus can cause a monomicrobial necrotizing fasciitis and should be empirically covered by the initial antibiotic regimen while awaiting microbiologic confirmation. However, the intraoperative tissue specimen from this patient reveals gram-negative bacilli and not gram-positive cocci in clusters that would herald a MRSA infection.

Mycobacterium marinum skin infections typically develop at sites of skin injury that have been exposed to salt or fresh water, such as in fish tanks (fish tank granuloma). The upper extremity is often involved and lesions are usually papular before becoming ulcerative. Systemic toxicity is not usually seen in skin infections caused by this nontuberculous acid-fast bacillus. The Gram stain of infected tissue would be negative.