PmrA Gene Polymorphism and Mutation in Colistine-Resistant Acinetobacter Baumannii Strains

Acinetobacter baumannii has been identified as the major cause of nosocomial outbreaks associated with high morbidity and mortality worldwide in recent years. It is one of the most frequently isolated agents in nosocomial infections, especially in intensive care units. The limited number of antibiotics that can be used in the treatment of multiple drug resistant (MDR) A. baumannii infections causes serious clinical problems. The decreasing number of antibiotic options combined with the increase in the frequency of infections with Gram negative bacteria with MDR and the problems experienced in their treatment have necessitated the reuse of older antibiotics such as colistin and other polymyxins. Colistin resistant A. baumannii strains have been reported following its use in treatment. The main mechanism of colistin resistance in A. baumannii is the addition of a cationic group to the lipopolysaccharide (LPS) layer due to mutation in the PmrAB gene region. In our study, we aimed to determine the PmrA gene polymorphism and mutation in colistin-resistant A. baumannii isolates obtained from clinical samples and to understand the phylogenetic relationship between PmrA genes. A total of 29 A.baumannii strains isolated between June 2019 and June 2020 from patients who received colistin treatment and were followed in intensive care units and services of the Research and Training Hospital of RTE University were used to perform sequence analysis. Phylogenetic analysis was performed in Clustal 2.1 Multiple Sequence Alignment using the reference strain AB030 of the A. baumannii. Sequencing of the PCR products of the strains that were PmrA positive revealed, point mutations (SNP) spread to the entire amplified region, which were relatively higher in the first 60 bp. It was determined that there were 6 strains that differed from the reference strain with the SNPs examined. When our study was evaluated in terms of phylogenetic relationship, the mutations that occurred in the samples were closely related to each other. Our finding that mutations detected in the 175 bp region of the PmrA gene are related to the resistance of the colistin, suggests that mutations in this region may be related to the resistance of the colistin. Sequence analysis of the PmrA gene region and determination of the resulting changes; it is one of the first studies in this field in our country. We think that this study will pave the way for new studies to be carried out in this field. New generation genome technologies are a very good option for fully revealing the resistance mechanism of colistin in MDR A. baumannii isolates. However, because of the high cost of technologies, reference centers should be established on this subject and resistant strains identified in the country should be further investigated here.