BACKGROUND
The slow-growing nontuberculous mycobacterium Mycobacterium marinum inhabits aquatic environments and causes cutaneous infections following minor trauma sustained during aquatic activities. It causes skin and soft-tissue infections with nonspecific clinical manifestations, frequently resulting in delayed diagnosis due to slow growth that requires specialized laboratory conditions. Diagnostic delay often leads to inappropriate antimicrobial therapy and unnecessary surgical interventions.
CASE REPORT
We describe 3 patients, 1 of whom had received immunosuppressive biologic therapy prior to diagnosis, with M. marinum infection, in whom prolonged diagnostic delays led to advanced disease involving soft tissue, tendon, and bone. Initial presentations mimicked common conditions such as cellulitis or inflammatory dermatoses, and all patients failed standard empiric therapy. Progressive disease included tenosynovitis, sporotrichoid spread, and osteomyelitis. Imaging, particularly magnetic resonance imaging, was instrumental in identifying deep-tissue involvement and guiding biopsy. Diagnosis was established through histopathology, mycobacterial culture under specialized conditions, and polymerase chain reaction testing, including culture-negative cases. All patients required prolonged multidrug therapy with macrolide- and rifampin-based regimens; 1 patient required repeated surgical debridement.
CONCLUSIONS
These cases illustrate that delayed recognition of M. marinum infection, regardless of baseline immune status, may coincide with progression to deep-tissue disease and prolonged morbidity. Failure of conventional antibiotics, history of aquatic exposure, and chronic or progressive symptoms should prompt early biopsy, targeted cultures, and molecular diagnostics. Early imaging and structured diagnostic evaluation are critical to prevent progression to deep infection, reduce morbidity, and avoid unnecessary interventions. Heightened clinical suspicion is particularly important in regions with frequent aquatic exposure.

Keywords: Osteomyelitis; Mycobacterium Infections, Nontuberculous; Mycobacterium marinum; Aquatic Organisms; Waterborne Diseases