Investigation of the , , , , and efflux pump genes expression among multidrug-resistant clinical isolates.

BACKGROUND

Different resistance mechanisms for multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) have been reported. Although mutations in target genes are the main cause of drug resistance, efflux pumps (Eps) also play an important role in this process. Here, we investigated the overexpression of five putative EP genes plus gene mutations in MDR-TB clinical isolates.

METHODS

A total of 27 (Mtb) clinical isolates including, 22 MDR and 5 sensitive isolates were analyzed. Minimum inhibitory concentrations (MIC) were determined in the absence and presence of efflux inhibitor. The expression level of 5 EP genes (, , , , ) was investigated by quantitative real time PCR (RT-qPCR). DNA sequencing of , , and promoter was done.

RESULTS

Among the 22 MDR-TB isolates, 13 (59.1%) showed significant overexpression (>4-fold) for at least one EP gene. The expression levels of 5 genes were significantly higher (P < 0.05) in MDR-TB isolates than sensitive isolates. The (22.7%), and (18.2%) were found to be the most commonly overexpressed EPs. The observed MICs were as follows: RIF (2 to >128 μg/ml) and INH (2-32 μg/ml). After efflux pump inhibitor exposure, 10/22 (45.45%) isolates showed a decrease in MIC of INH, and 17/22 (77.27%) isolates showed a decrease in MIC of RIF. Of the isolates that overexpressed, 4 isolates lacked mutation in , , and genes and 10 ones lacked mutation in and .

CONCLUSION

The results showed that overexpression of EP genes in Mtb isolates, besides target gene mutations can contribute to the development of MDR phenotype.