Fish Tank-Associated <i>Mycobacterium Marinum</i> Infection in an Immunocompromised Host

<i>Mycobacterium marinum</i> infection can be challenging to diagnose and treat, especially in immunocompromised patients on tumour necrosis factor alpha inhibitors. A patient with collagenous colitis on infliximab presented with ulcerated plaques accompanied by nodules in a sporotrichoid fashion. Initial treatments failed until a biopsy confirmed <i>M. marinum</i> Multiple antibiotic regimens, including rifampicin and ciprofloxacin, were required due to resistance. The case underscores the importance of patient education on avoiding aquatic environments, considering atypical mycobacterial infections in differentials for immunocompromised patients with sporotrichoid lesions, and prioritising urgent diagnostic biopsies. Treatment can be lengthy, often requiring up to 12 months, emphasising the need for ongoing patient counselling and multidisciplinary management. Current guidelines recommend a combination of ethambutol and macrolides, though further research is necessary to optimise treatment protocols.