Molecular detection of adeB, tetA and tetB efflux pump genes in clinical isolates of Acinetobacter baumannii and evaluation of their role in resistance to ciprofloxacin and tetracycline

Abstract

Multidrug-resistant Acinetobacter baumannii are increasing and cause nosocomial infections with high morbidity and mortality rate, especially in long- hospitalized and immunocompromised patients. Among different antibiotic resistance mechanisms, efflux pumps play a vital role. This descriptive cross-sectional research was conducted in the first six months of 2018. In this study, 50 isolates of A. baumannii were obtained from patients admitted to different ICU sections. The antibiotic resistance pattern was investigated by the disk diffusion method according to CLSI guideline (2015). Out of 50 A. baumannii isolates, 9 of them identified as extensively drug resistant (XDR). Minimum inhibitory concentration was measured for ciprofloxacin and tetracycline in the presence and absence of CCCP for XDR isolates. The prevalence of tetA, tetB and adeB efflux pump genes was investigated using polymerase chain reaction for all isolates. Moreover, the expression of the adeB gene was investigated by Real-time PCR and Ethidium bromide agar cartwheel method for tetracycline-resistant isolates. In this study, the highest antimicrobial resistance was to cefotaxime/clavulanic acid (92%) and no isolate was resistant to colistin. The prevalence of MDR and XDR isolates was 68 and 18% respectively. In XDR isolates, the MIC of tetracycline reduced in the presence of CCCP whereas the MIC of ciprofloxacin was unchanged. The prevalence of tetA, tetB and adeB was 10, 62 and 100%, respectively. Real-time PCR and EtBr-agar cartwheel results showed that adeB was overexpressed in tetracycline-resistant isolates. According to our results, using efflux pump inhibitors can be useful in the treatment of nosocomial infection due to MDR and XDR A. baumannii. Moreover, EtBr-agar cartwheel is a reliable method for the evaluation of the efflux pumps expression in clinical laboratories.

Keywords: Acinetobacter baumannii, antimicrobial resistance, efflux pump.