First detection of insertion sequences ISpa1635 and IS1411 among non-carbapenemase producing strains of Pseudomonas aeruginosa in Kerman, Iran

Abstract

BackgroundLoss of OprD, AmpC overproduction and efflux pump over activity are the main mechanism for chromosomally resistance to carbapenems in Pseudomonas aeruginosa. In this study, we investigated the chromosomally resistance mechanism to carbapenems among 9 non-carbapenemase-producing P. aeruginosa (NCPPa). Material and methodAntibacterial resistance was determined by disc diffusion method among 170 clinical isolates of P. aeruginosa. Sixty-one isolates were multiple drug resistance and resistance to imipenem, and 9 isolates (5.3%) were negative for ten carbapenemase genes and were recognized as NCPPa. To determine the mechanism of resistance in NCPPa isolates AmpC and efflux pump overproduction were evaluated. Overexpression of MexAB-oprM efflux pump system was evaluated by qReal-time PCR. Also, oprD gene sequenced to detect any insertional and point mutations. ResultsAll NCPPa isolates shown a significant overexpression of mexA gene in qReal-time PCR experiment, while 88.8% of the isolates had overproduced AmpC enzyme. Finally, oprD gene was destructed by two insertion sequences (ISs), including IS1411 and ISpa1635. ConclusionAccording to the results of this study, overexpression of efflux pumps, oprD mutation and AmpC overproduction are the main chromosomal mechanism of resistance of P. aeruginosa to carbapenems in NCPPa isolates in this study.