Drug Susceptibility Testing of Mycobacterium Simiae: An Emerging Pathogen in Iran

Introduction: Mycobacterium simiae is an emerging pathogen in Iran and little is known about drug susceptibility patterns of this pathogen. Materials and Methods: Twenty-five clinical isolates of M. simiae from 80 patients with confirmed NTM pulmonary disease were included in this study. For drug susceptibility testing (DST), proportional and broth microdilution methods were used according to the clinical and laboratory standards institute (CLSI) guideline. Results: All clinical isolates of M. simiae were resistant to isoniazid, rifampicin, ethambutol, streptomycin, amikacin, kanamycin, ciprofloxacin, and clarithromycin. They also were highly resistant to ofloxacin (80%). Susceptibility to ofloxacin was only noted in the 5 isolates. Conclusion: Clinical isolates of M. simiae were multidrug-resistant, and had different drug susceptibility patterns than previously published studies. DST results can assist in selecting more appropriate treatment regimens. Newer drugs with proven clinical efficacy correlating with in vitro susceptibility should be substituted with first- and second-line anti-TB drug testing.