Evaluation of Polymyxin B Susceptibility Profile and Detection of Drug Resistance Genes among Acinetobacter Baumannii Clinical Isolates in Tehran, Iran during 2015-2016.

Acinetobacter baumannii is an important opportunistic pathogen, responsible for approximately 10% of all gram-negative nosocomial infection. The aim of this study was to determine aminoglycoside and quinolone resistance genes and their antimicrobial susceptibility profile in the clinically A. baumannii. In this cross-sectional study, a total of 100 nonduplicative A. baumannii isolates were collected from different clinical samples. Antimicrobial susceptibility test was performed by disk diffusion method. QnrA, anrB, qnrS, aac(3)-IIa, and aac(6')-Ib genes were identified using PCR method. The results of antibiotic susceptibility test showed that polymyxin B was the most effective antimicrobial against A. baumannii. 97%, 95% and 82% of isolates were resistant to cefepime, ceftriaxone, and amikacin, respectively. The molecular distribution of aac(3)-IIa, aac(6')-Ib, and qnrA genes were 45%, 50%, and 50% of isolates, respectively. However, qnrB and qnrS genes could not be detected in any strain. This study showed that polymyxin B was the best drug against A. baumannii clinical isolates. This data is also valid for polymyxin E (colistin), which is mostly used in clinics. There is a high level of resistance genes among clinical A. baumannii isolates. This high prevalence rate highlights the necessity for the development of rapid diagnostic assays and continuous monitoring of antibiotic resistance.