Drug susceptibility testing of nontuberculous mycobacteria

Diseases caused by nontuberculous mycobacteria are emerging in many settings. With an increased number of patients needing treatment, the role of drug susceptibility testing is again in the spotlight. This articles covers the history and methodology of drug susceptibility tests for nontuberculous mycobacteria, but focuses on the correlations between in vitro drug susceptibility, pharmacokinetics and in vivo outcomes of treatment. Among slow-growing nontuberculous mycobacteria, clear correlations have been established for macrolides and amikacin (Mycobacterium avium complex) and for rifampicin (Mycobacterium kansasii). Among rapid-growing mycobacteria, correlations have been established in extrapulmonary disease for aminoglycosides, cefoxitin and co-trimoxazole. In pulmonary disease, correlations are less clear and outcomes of treatment are generally poor, especially for Mycobacterium abscessus. The clinical significance of inducible resistance to macrolides among rapid growers is an important topic. The true role of drug susceptibility testing for nontuberculous mycobacteria still needs to be addressed, preferably within clinical trials.