Which Mycobacterium species is most commonly associated with contamination of hot water systems in large institutions?

• A. M. xenopi
• B. M. haemophilum
• C. M. marinum
• D. M. ulcerans

Answer: (A)

Hot-water plumbing in large facilities provides an environment where hardy environmental mycobacteria can persist. Mycobacterium xenopi is especially linked to contamination of hot water systems because it grows well at elevated temperatures typical of hospital hot-water outlets and readily colonizes biofilms in plumbing. This thermophilic tendency makes it a frequent finding in institutional water systems and it can lead to pulmonary infections in susceptible individuals exposed to the water. Other non-tuberculous mycobacteria have different ecological niches: Mycobacterium marinum is tied to cooler aquatic settings like fish tanks and swimming pools and causes skin infections after water exposure; Mycobacterium haemophilum prefers cooler temperatures and iron-rich environments, often presenting with cutaneous or disseminated disease in children or immunocompromised patients; Mycobacterium ulcerans is associated with tropical freshwater environments and causes Buruli ulcer rather than hot-water system–related infections.