Unexpected Threat: Cutaneous Mycobacterium marinum from a Chestnut Thorn

Nontuberculous mycobacterial infections are typically seen in immunocompromised individuals; however, Mycobacterium marinum is a rare pathogen that can also affect immunocompetent hosts.It generally presents as a non-disseminated cutaneous infection limited to the skin and soft tissues, showing manifestations like papules, plaques, or single/multiple lesions.Water and fish exposures are well-known risk factors.However, our case shows no history of aquatic exposure; instead, the patient reports a chestnut thorn injury at the affected site.The differential diagnosis should include other granulomatous infections and autoimmune diseases.Species-level identification is essential for the disease diagnosis, but it is not feasible in every center.M. marinum is generally susceptible to ethambutol, rifampicin, sulfonamides, and macrolides.By contrast, our case reveals an unexpected resistance pattern.The species-level identification and the antibiotic susceptibility testing are of paramount importance for establishing accurate diagnosis and ensuring effective treatment.