[The effects of gene mutation related to drug resistance and drug efflux pump in extensively drug-resistant tuberculosis clinical isolates].

OBJECTIVE

To explore the effects of 2 major drug-resistant mechanisms in clinically isolated strains of extensively drug-resistant tuberculosis (XDR-MTB).

METHODS

Genomic DNA of 10 XDR-MTB strains isolated from Shanghai Pulmonary Hospital were extracted. The main gene mutations related to drug resistance and 15 SNPs unique to XDR-MTB clinical isolate KZN605 reported by the Broad Institute in USA were detected by sequencing. The changes of minimal inhibition concentration (MIC) of XDR-MTB isolates were detected before and after the addition of efflux pump inhibitors verapamil, CCCP and reserpine in liquid cultures.

RESULTS

The mutation of rpoB, katG and rpsL occurred in all XDR-MTB strains. The mutation of gyrA, gyrB and rrs occurred in 9 strains, 2 strains and 6 strains respectively. There was no mutation of tlyA in all the strains. Most of the SNPs in KZN 605 strains were not detected in the clinical strains. The clinical strains showed no significant changes of MICs, except 1 strain for which the MIC of ofloxacin decreased by 16 times after addition of the efflux pump inhibitors.

CONCLUSIONS

The gene mutations related to drug resistance are the key mechanism for the clinical XDR-MTB strains, while the efflux pumps partly play a role in the drug resistance to fluoroquinolones. The detailed mechanism of efflux pump mediated drug resistance to other anti-TB drugs needs further study.