ABSTRACT
AcrAB-TolC is a tripartite efflux pump system constitutively expressed which functions as an intrinsic-resistant mechanism found to be responsible for conferring resistance towards dyes, detergents and different compounds including various classes of antibiotics. One global regulator belonging to AraC-type regulator family, regulator of antibiotic resistance A (RarA) up-regulates the expression of AcrAB-TolC encoded in Klebsiella pneumoniae, Enterobacter sp. 638, Serratia proteamaculans 568 and Enterobacter cloacae resulting in multidrug-resistant phenotypes. The present work was initiated to find out the transcriptional response of RarA in clinical isolates of Escherichia coli against concentration gradient carbapenem stress. A total of 22 clinical isolates of E. coli and expression level of regulators were analysed via quantitative real-time polymerase chain reaction with and without carbapenem stress. As a result, a strong correlation between the expressional levels of RarA in AcrAB overexpressed isolates of E. coli and elevated expression was observed when exposed under concentration gradient ertapenem stress. The clones containing pRar showed reduction in the zone of inhibition towards carbapenem, indicating the active participation of RarA in AcrAB overexpressed isolates of E. coli conferring resistance towards carbapenems.