A challenging case of refractory infection following fish fin injury: Successful treatment through combined therapy

We report a case of refractory infection caused by Mycobacterium marinum and Mycobacterium shottsii following a fish fin injury. The diagnosis was confirmed by acid-fast bacilli staining and metagenomic next-generation sequencing. This case posed challenges in diagnosis and treatment due to the simultaneous infection by acute and chronic pathogens, uncommon skin and joint symptoms, and multiple lesions involving deep fascia and intermuscular spaces caused by special pathogens. Ultimately, resolution of the lesions without recurrence was achieved after the thorough surgical debridement and excision of the affected tissue in conjunction with dual antibiotic therapy. This success highlights that optimal outcomes require both the most thorough lesion clearance possible and adequate antibacterial therapy administered concurrently.

Notably, M. shottsii—previously undocumented as a human pathogen—was identified in this case, expanding the known spectrum of mycobacterial pathogens and highlighting a previously unrecognized zoonotic risk.