Antimicrobial susceptibility testing and genotyping of Mycobacterium avium isolates of two tertiary tuberculosis designated hospital, China

- This is the first systemic assay on the bacteriological feature of M. avium isolated from China.
- We firstly found that 16-loci VNTR genotyping method is more discriminative in northern China than in southern China.
- Our study stressed the importance of building up knowledge from the local M. avium isolates.

Background: Mycobacterium avium is frequently isolated from clinical samples, while the bacteriological features of M. avium clinical isolates from China have never been well defined.Methods: A total of 50 M. avium isolates were recruited from two tertiary tuberculosis designated hospitals, one located in Beijing whereas another in Fujian Province, which are northern and southern parts of China, respectively. Subspecies identification was conducted by sequencing the variable 3′ end of the hsp65 gene. The susceptibility against 15 antimicrobial agents, widely administered for the 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: All of the 50 M. avium isolates were identified as M. avium subsp. hominissuis. The drug susceptibility test revealed that clarithromycin (98%, 49/50) and moxifloxacin (86%, 43/50) had the best antimicrobial activities in vitro against the M. avium isolates. The overall Hunter-Gaston Discriminatory Index (HGDI) value for the VNTR typing was 0.95. However, the genotyping method yielded much greater discriminative power for isolates of northern China than that of southern China (1.00 V.S. 0.86, P < 0.05).Conclusion: M. avium subsp. hominissuis is the dominate subspecies among M. avium clinical isolates in China. The 16-loci VNTR genotyping method is more discriminative in Beijing than in Fujian Province. The bacteriological features of M. avium isolates from different regions of China demonstrated dramatic variations, and stressed the importance of building up knowledge from the local isolates.