In vitro Susceptibility of Nontuberculous Mycobacteria in China

Abstract Background: Precise species or subspecies identification of NTM clinical isolates is important for managing patients with NTM diseases. It is of great necessity to measure the prevalence of resistance to antimicrobial agents, and explore the risk factors associated with drug resistance by using NTM isolates from China. Methods: A total of 355 NTM isolates were included in our analysis. Broth dilution method was used to determine in vitro drug susceptibility of NTM isolates. Results: Clarithromycin (CLA) was the most potent drug for Mycobacterium intracellulare (MI). The resistance rate to CLA was 21%, yielding a minimum inhibitory concentrations (MIC)50 and MIC90 of 8 and 64 mg/L, respectively. 51% of MI isolates exhibited resistance to amikacin (AMK). For MABC, 6 and 49 isolates were categorized as resistant to CLA at Day 3 and 14, respectively. The resistance rate to CLA for Mycobacterium abscessus subspecies abscessus (MAA) was dramatically higher than that for Mycobacterium abscessus subspecies massiliense (MAM). Additionally, the percentage of patients presenting fever in the CLA-susceptible group was significantly higher than that in the CLA-resistant group. Conclusions: Our data demonstrate that approximate one fifth of MI isolates are resistant to CLA. MAA is more resistant to CLA than MAM. The clinical manifestations of MI-infected patients caused by CLA-resistant bacilli seem to be milder than in CLA-susceptible group.