Molecular mechanisms of colistin resistance mediated by pmrCAB genes in Acinetobacter baumannii isolated from patients hospitalized in Isfahan medical centers

Abstract

Abstract Introduction In recent years, colistin-resistant Acinetobacter baumannii (A. baumannii) has been found all over the world. In this current study, the main purpose was to examine the occurrence of extensively drug resistant (XDR), resistance to colistin and characterization and mutations in pmrCAB genes among A. baumannii obtained from inpatients. Materials and Methods A total of 108 clinical isolates of A. baumannii were collected from several hospitals located in Isfahan, Iran. The Kirby-Bauer assay was performed to assess the antimicrobial resistance. The Phoenix automated system was utilized to determine the minimum inhibitory concentration (MIC) of colistin for each of the bacterial isolates. Polymerase chain reaction was used to screen for pmrCAB genes that mediate colistin resistance, and sequencing was used to determine the amplicon’s nucleotide sequence. Results The results revealed that all A. baumannii isolates (100%) were resistant to piperacillin tazobactam, meropenem and ciprofloxacin. All isolates were classified as XDR, with seven isolates being pan-drug resistant (PDR). Colistin resistance (CoR) was found in 6.48% (7/108) of studied isolates, all of which were positive for pmrCAB genes. The sequencing results showed a substitution in pmrB and two isolates showed a substitution in pmrC. Conclusions In conclusion, this study is the initial report of the existence and mutations of pmrB and C genes in the clinical isolate of A. baumannii in our region. This outcome highlights the necessity to explore additional mutations in the PMR operon of A. baumannii in forthcoming studies. Moreover, our results highlight the high occurrence of XDR-A. baumannii strain in Isfahan, Iran.