Abstract / Summary
Nontuberculous Mycobacterium (NTM) species are increasingly recognized as opportunistic pathogens in companion animals, yet data on species distribution and antimicrobial resistance remain limited. The goal of this study was to evaluate species identification methods and to determine the antimicrobial susceptibility profiles of NTM isolates obtained from cat and dog samples submitted to the University of Tennessee Veterinary Diagnostic Laboratory. Twenty-nine NTM isolates (25 feline, 4 canine) collected between 2016 and 2022 were cultured and identified using MALDI-TOF MS and 16S rRNA sequencing. Antimicrobial susceptibility testing (AST) was performed by broth microdilution. MALDI‑TOF MS identified 25 isolates to the species level. The isolates were classified into four rapidly growing mycobacterial groups: 12 isolates within the Mycobacterium fortuitum complex, 10 isolates within the M. smegmatis group, 4 isolates within the M. abscessus group, and 1 isolate within the M. mucogenicum group. Four isolates, including two slow‑growing strains, were not identified by MALDI‑TOF MS but were identified and grouped based on 16S rRNA sequencing. There was limited agreement in species‑level identification between the two primer sets used. AST revealed consistent susceptibility to amikacin and moxifloxacin, while resistance was highest to doxycycline (41%), clarithromycin (37%), and tobramycin (33%). Rapidly growing NTM predominates in feline cutaneous infections, with species-specific resistance patterns underscoring the need for accurate identification and AST to guide therapy.