[Antimicrobial susceptibility and genotyping of Mycobacterium intracellulare].

Objective

To investigate the antimicrobial susceptibility and genotyping of Mycobacterium intracellulare.

Methods

A total of 150 M. intracellulare isolates were collected. The susceptibility against 15 antimicrobial agents widely used for treatment of non-tuberculosis mycobacteria (NTM) infections, was tested by broth microdilution assay. Variable number of tandem repeats (VNTR) assay was also performed using the 16-loci genotyping method.

Results

The drug susceptibility test revealed that clarithromycin (97.3%, 146/150), moxifloxacin (94.0%, 141/150) and amikacin (90.0%, 135/150) had the best antimicrobial activities in vitro against the M. intracellulare isolates. Secondly, 75.3%(113/150), 64.0%(96/150), 52.7%(79/150) and 8.7%(13/150) of the strains were susceptible to rifampicin, linezolid, capreomycin, and ethambutol, respectively. The MIC(50) and MIC(90) values of the 3 injectable anti-tuberculosis drugs were as follows: amikacin 4 mg/L and 16 mg/L, streptomycin 4 mg/L and 16 mg/L, capreomycin 8 mg/L and 16 mg/L. The MIC(50) and MIC(90) values of the 5 different fluoroquinolones were 0.5 mg/L and 2 mg/L for moxifloxacin , 1 mg/L and 8 mg/L for ciprofloxacin, 1 mg/L and 8ug/ml for levofloxacin, 2 mg/L and 16 mg/L for antoflolxacin, 2 mg/L and 16 mg/L for ofloxacin. The Hunter-Gaston Discriminatory Index (HGDI) value for the 16-loci VNTR typing of M. intracellulare isolates was 0.994. VNTR differentiated the 150 isolates into 21 clusters and acquired a total of 121 unique patterns. Drug resistance profile was not independently associated with cluster strains.

Conclusions

Clarithromycin, moxifloxacin and amikacin had the best antimicrobial activities in vitro against M. intracellulare isolates. The 16-loci VNTR typing revealed a highly discriminatory power and drug resistance profile was not independently associated with cluster strains.