Microarray Analysis of Efflux Pump Genes in Multidrug-Resistant Mycobacterium tuberculosis During Stress Induced by Common Anti-Tuberculous Drugs

Treatment of multidrug-resistant tuberculosis has become one of the major problems in public health. Understanding the molecular mechanisms of drug resistance has been central to tuberculosis research in recent times. DNA microarray technology provides the platform to study the genomic variations related to these mechanisms on a comprehensive level. To investigate the role of efflux pumps in drug resistance, we have constructed a custom DNA microarray containing 25 drug efflux pump genes of Mycobacterium tuberculosis (Indian Patent file no. 2071/DEL/2007) and monitored changes in the expression of these genes on exposure of common antituberculous drugs. Expression profiling of efflux pump genes in multidrug-resistant M. tuberculosis isolates showed overexpression of 10 genes following exposure to various anti-tuberculous drugs. Although two of these genes (Rv3065 and Rv2938) have already been reported to be active drug efflux pumps in M. tuberculosis in earlier studies, the increased activities of other eight efflux pump genes (Rv1819, Rv2209, Rv2459, Rv2477c, Rv2688, Rv2846, Rv2994, and Rv3728) have been demonstrated in multidrug-resistant isolates by us for the first time. After confirmation of differential expressions of these genes by real-time reverse transcription polymerase chain reaction, it was observed that a simultaneous overexpression of efflux pump genes Rv2459, Rv3728, and Rv3065 was associated with resistance to the combination of isoniazid and ethambutol, and these drugs, along with streptomycin, were identified to group together, where efflux-mediated drug resistance appears to be important in M. tuberculosis and follows a constant pattern of induction in multidrug-resistant isolates. Isoniazid and ethambutol combination was also found to be affected in 10% (6/60) of the clinical isolates in the presence of carbonyl cyanide m-chloro phenylhydrazone in resazurin microtitre plate assay, supporting the role of efflux pumps in the resistance to these drugs. Overexpression of two of the genes (Rv2477 and Rv2209) has also been observed with ofloxacin stress in M. tuberculosis.