Role of mexZ gene in ciprofloxacin resistance in Pseudomonas aeruginosa isolates in Guilan province

Pseudomonas aeruginosa is an opportunistic pathogen and one of mortality causes of nosocomial infections specifically in severely burned patients. One of the drug resistant mechanisms in pseudomonas aeruginosa is mutation in negative regulator genes of mexXY efflux pump system. In this study, the role of mexZ mutations was investigated in ciprofloxacin resistant development in Pseudomonas aeruginosa isolates in Guilan province.
In this study, 45 strains of pseudomonas aeruginosa isolated from different clinical samples of Rasht and Lahijan hospitals and laboratories between 2014 to 2016 were identified by biochemical tests. The antibiotic resistance and susceptibility of the strains were investigated by Kirby Bauer method and MIC determination. Then PCR-sequencing was performed to assess MexZ gene mutations in ciprofloxacin resistant strains.
From 45 isolates of pseudomonas aeruginosa, all were resistant to cefixime, cephalothin and trimethoprim; whereas 17 isolates were ciprofloxacin resistant. The highest MIC of ciprofloxacin was determined 1024 µg/ml. Also, PCR-sequencing analysis showed that 8 isolates had missense mutations in MexZ gene such as L111E and R143P.
In this study, mutation in mexZ as negative regulator of mexXY can be a reason of multi-drug resistance in some strains in Guilan province. It appears that mexZ mutation led to affinity modification in mexZ protein binding to DNA in some isolates.