Transcriptional expression of PmrB and arnA within polymyxin-resistant nosocomial isolates of Pseudomonas aeruginosa from India

Objective: The polymyxin group of antibiotics is considered to be one of the most effective antimicrobial agents against many serious pathogenic bacteria, but the excessive use of these antibiotics has led to the development of drug resistance among bacteria. This study was designed to characterize polymyxin-resistant P. aeruginosa and to explore the role of PmrB and arn A in resistant phenotype. Methods: mRNA and cDNA of five selected polymyxin-resistant strains representing different MIC range; isolated under normal condition of  strain growth, after treating sample/media with FeCl3 and MgCl2 alone, or after treating with FeCl3 and polymyxin antibiotic. The transcriptional expression was observed for PmrB and arn A by quantitative real time RT-PCR in reference to P. aeruginosa PAO1. The presence of plasmid mediated colistin resistance determinants mcr-1 was screened by PCR. Susceptibility of the strains was determined by disc-diffusion method and DNA fingerprinting was carried out by performing REP-PCR. Results: A down regulated expression of PmrB and arn A was observed even after the unique induction with FeCl3 and MgCl2. All the isolates were found to be resistant against cefepime and different clonal patterns of resistance were found among the isolates. Conclusion: This study has drawn a new insight into polymyxin resistance which will help in the detection and control of infections caused by multidrug resistant P. aeruginosa . The low susceptibility rate to aminoglycoside, piperacllin-tazobactam and ciprofloxacin was found and in addition, detection of PmrB and arn A as molecular markers in the follow up of infections caused by multidrug resistant P. aeruginosa . J Microbiol Infect Dis 2018; 8(2):61-68.