American Board of Internal Medicine (ABIM) Certification Practice Exam

What type of skin infections does Mycobacterium marinum typically cause?

1. Burn infections

2. Fish tank granuloma

3. Necrotizing fasciitis

4. Cellulitis

The correct answer is: Fish tank granuloma

Mycobacterium marinum is a type of mycobacterium that is primarily associated with aquatic environments, particularly fresh and saltwater, and is commonly linked to fish tanks or aquariums. The infections caused by this organism are often referred to as "fish tank granuloma." These infections occur when the bacteria enter the skin through abrasions when individuals come into contact with contaminated water, such as during activities involving fish tanks, aquariums, or swimming in natural waters. The hallmark presentation of a Mycobacterium marinum infection is a localized granulomatous dermatitis, which can progress to form nodules, ulcers, or longstanding granulomas, typically in areas exposed to the aquatic environment. This specific association with water exposure and fish handling is crucial for identifying the cause of the skin infection, making "fish tank granuloma" the appropriate designation for these types of infections. Other forms of skin infections listed do not directly correlate with Mycobacterium marinum. This organism is not known to cause burn infections, necrotizing fasciitis, or cellulitis, which are associated with different pathogens or mechanisms of infection. Understanding these distinctions is key in the diagnosis and treatment of skin infections.