In vitro bactericidal assay of linezolid on multidrug-resistant tuberculosis and nontuberculous mycobacteria

Abstract

Objective To investigate the mycobactericidal efficacy of linezolid on multidrug-resistant tuberculosis (MDR-TB)and nontuberculous mycobacteria (NTM) in vitro. Methods Seven hundred and sixty-two Mycobacterium tuberculosis and 20 NTM isolates from Hangzhou were identified by using hsp65 gene sequencing from March to June, 2013. Seventy MDR-TB isolates, which were screened by using proportion method, and twenty NTM isolates were tested the MIC to linezolid，and the differences of MICs to linezolid between MDR-TB and NTM werw analyzed in vitro. Results All 70 MDR-TB isolates were inhibited at concentrations of ≤1 mg/L by linezolid, MIC50 was 0.5 mg/L and MIC90 1 mg/L. Of all 8 isolates inhibited at concentration of 1 mg/L，there were 6 isolates resistant to isoniazid, rifampin, streptomycin and ethambutol, suggesting this resistance pattern may reduce sensitivity to linezolid. Among the NTM isolates, 18 Mycobacterium intracellulare isolates, whose MICs to linezolid at 8-16 mg/L, were non-resistant isolates, while 2 Mycobacterium abscessus isolates displaying MICs＞32 mg/L, were resistant to linezolid. Conclusions Linezolid showed great activity to MDR-TB and there were no linezolid-resistant MDR-TB isolates identified in this study. However, MICs of MDR-TB against linezolid increased with their resistant numbers to first-line agents. This study also showed that different NTM species have varied sensitivity to linezolid. （Chin J Lab Med,2014,37:535-538） Key words: Mycobacterium tuberculosis; Nontuberculous mycobacteria; Drug resistance, multiple, bacterial