Antimicrobial susceptibility patterns and genotypic characteristics of Mycobacterium marinum and Mycobacterium abscessus isolated from cutaneous infections: A retrospective study.

OBJECTIVES

Antimicrobial susceptibility data for cutaneous mycobacteria remain limited. This study investigated the antimicrobial susceptibility patterns and molecular resistance mechanisms of Mycobacterium marinum and Mycobacterium abscessus isolates from a dermatology specialized hospital in China.

METHODS

Antimicrobial susceptibility testing was performed on 200 M. marinum and 50 M. abscessus clinical isolates using broth microdilution method. M. abscessus subspecies were identified through hsp65, erm (41), and rpoB gene sequencing. For M. abscessus isolates, resistance-associated mutations for clarithromycin, amikacin, and fluoroquinolones were analysed by sequencing erm (41), rrl, rrs, gyrA, and gyrB genes.

RESULTS

M. marinum demonstrated high susceptibility (82.5%-100%) to clarithromycin, rifampin, rifabutin, moxifloxacin, linezolid, trimethoprim-sulfamethoxazole, with moderate susceptibility to tetracyclines and ciprofloxacin. Ethambutol showed favourable activity against M. marinum with MIC90 of 2 µg/mL. Among M. abscessus isolates (23 M. abscessus subsp. abscessus, 26 M. abscessus subsp. massiliense, 1 M. abscessus subsp. bolletii), overall susceptibility to clarithromycin and amikacin was 78% and 82%, respectively. Tigecycline and clofazimine were effective against M. abscessus with MIC90 1 and 0.5 µg/mL, respectively. In contrast, M. abscessus isolates demonstrated high-level of resistance to multiple antibiotics, including linezolid, fluoroquinolones, and tetracyclines. M. abscessus subsp. massiliense exhibited higher clarithromycin susceptibility (100%) compared to M. abscessus subsp. abscessus (56.5%). Clarithromycin resistance of M. abscessus isolates correlated with functional T28 sequevar in the erm (41) gene.

CONCLUSIONS

Our findings elucidate distinct antimicrobial susceptibility profiles of M. marinum and M. abscessus isolated from cutaneous infection in China, providing critical guidance for clinical treatment. Cutaneous M. abscessus isolates exhibit extensive drug resistance patterns. Subtyping and erm (41) polymorphism detection serve as reliable predictors of clarithromycin resistance in M. abscessus.