Drug susceptibility distributions of

Recent outbreaks of cardiac surgery-associated Mycobacterium chimaera infections have highlighted the importance of species differentiation within the Mycobacterium avium complex and pointed to a lack of antibiotic susceptibility data for M. chimaera. Using the MGIT 960/EpiCenter TB eXiST platform, we have determined antibiotic susceptibility patterns of 48 clinical M. chimaera isolates and 139 other nontuberculous mycobacteria, including 119 members of the M. avium complex and 20 Mycobacterium kansasii isolates toward clofazimine and other drugs used to treat infections with slow-growing nontuberculous mycobacteria (NTM). MIC(50), MIC(90), and tentative epidemiological cutoff (ECOFF) values for clofazimine were 0.5 mg/liter, 1 mg/liter, and 2 mg/liter, respectively, for M. chimaera. Comparable values were observed for other M. avium complex members, whereas lower MIC(50) (≤0.25 mg/liter), MIC(90) (0.5 mg/liter), and ECOFF (1 mg/liter) values were found for M. kansasii. Susceptibility to clarithromycin, ethambutol, rifampin, rifabutin, amikacin, moxifloxacin, and linezolid was in general similar for M. chimaera and other members of the M. avium complex, but increased for M. kansasii. The herein determined MIC distributions, MIC(90), and ECOFF values of clofazimine for M. chimaera and other NTM provide the basis for the definition of clinical breakpoints. Further studies are needed to establish correlation of in vitro susceptibility and clinical outcome.