Investigation of MexAB-OprM Efflux Pump Expression Level in Pseudomonas aeruginosa Strains Isolated from Patients Hospitalized in Shahid Motahari Hospital in Tehran City using Real-Time PCR method (Iran)

Drug resistance in Pseudomonas aeruginosa strains has become a worldwide problem, and efflux pumps are one of the major resistance mechanisms in this bacterium. The aim of this study was to identify the mutation in mexA and mexB pumps and to investigate the expression level of mexA pump in the isolates from burn patients.
This study was conducted as a descriptive study on 100 isolates of P. aeruginosa isolated from patients hospitalized in Shahid Motahari Hospital during 2014-2015. Antibiogram tests were performed using disc diffusion (according to CLSI guidelines). The inhibitory effect of carbonyl cyanide 3-chlorophenylhydrazone (CCCP), was assessed by broth microdilution method. Mutation in mexA and mexB genes, was detected by PCR and sequencing, and the expression level of mexA gene, was evaluated by real-time PCR and 2−ΔΔCT formula.
Ninety-five out of 100 isolates of P. aeruginosa, were resistant to imipenem. Sixteen isolates had response to the inhibitory effect, and a 4-fold reduction was observed in MIC results at the presence of this inhibitor. In one isolate, glycine was replaced by aspartic acid at position 257 of mexB protein sequence, but no change was seen in MexA. All isolates had mexA and mexB genes. Twenty percent of the isolates showed overexpression in mexA gene.
According to the results of this study, the antibiotic resistance as a result of overexpression of efflux pump, is of great concern. Hence, infection control by accurate management of drug prescription and identification of resistant isolates, is essential to prevent the spread of resistance.