Antimicrobial resistance of rapidly growing mycobacteria isolated from companion animals in Taiwan.

Rapidly growing mycobacteria (RGM) are omnipresent nontuberculous mycobacteria that cause opportunistic infections in animals and humans. Without knowledge of the epidemiology and antimicrobial susceptibility of RGM in companion animals in Taiwan, diagnostic and therapeutic regimens are limited. To address this, we collected 44 RGM isolates from 25 dogs and 19 cats from 2018 to 2021 and investigated their antimicrobial susceptibility and macrolide-resistance genes. The most prevalent RGM were Mycobacterium fortuitum complex (MFC), accounting for 20 isolates (14 dogs and 6 cats), and M. abscessus complex (MABC), accounting for 20 isolates (9 dogs and 11 cats). More than 80% of the RGM isolates were susceptible to linezolid and amikacin. All MABC isolates were resistant to at least three groups of essential antibiotics, including tetracyclines, fluoroquinolones, and trimethoprim-sulfamethoxazole, whereas 75% of MABC isolates were susceptible to clarithromycin. In contrast, 35% of MFC isolates were susceptible to clarithromycin, but these isolates varied in resistance to other antibiotics. The presence of inducible macrolide resistance was further confirmed by the coherence between the minimum inhibitory concentrations of clarithromycin and the presence of erm genes. In conclusion, our results showed that MABC and MFC are the major pathogens causing RGM infections in dogs and cats. The variability in their antimicrobial susceptibility profiles makes treatment challenging, particularly with the development of inducible resistance to macrolides. Local epidemiological data and comprehensive microbiological examinations are critical for diagnosis and treatment planning, whereas resistance gene detection aids in the rapid evaluation of RGM resistance to macrolides.IMPORTANCERapidly growing mycobacteria (RGM) are opportunistic pathogens in both humans and animals, posing significant challenges in diagnosis and treatment. The variable antimicrobial resistance profiles and inducible macrolide resistance complicate the design of multidrug regimens. Research on RGM infections in dogs and cats is limited, particularly studies examining inducible macrolide resistance. This study identified Mycobacterium abscessus complex and M. fortuitum complex as the predominant species in dogs and cats in Taiwan. Both species exhibited poor susceptibility to many antibiotics. M. fortuitum demonstrated lower minimum inhibitory concentration (MIC) values for fluoroquinolones and higher MIC values for clarithromycin, whereas M. abscessus complex showed the reverse pattern. Inducible macrolide resistance was present in our RGM isolates, and the detection of the erm genes provided a reliable prediction. These results support clinical diagnosis and the formulation of multidrug treatment regimens for RGM infections in dogs and cats.