Role of PA3574 (nalD) gene in development of ciprofloxacin resistance in Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa is a gram-negative opportunistic pathogen and one of the mortality causes of nosocomial infections. One of the drug resistance mechanisms in P.aeruginosa is mutation in negative regulator genes of mexAB-oprM efflux pump system such as nalD. The aim of this study was to investigate the role of nalD mutations in P. aeruginosa isolates of Guilan province in ciprofloxacin resistant development. In this study, 45 P. aeruginosa isolates were obtained from different clinical samples of Rasht and Lahijan hospitals and laboratories between 2014 to 2016 and identified by biochemical tests. Ciprofloxacin resistance and susceptibility of the strains was determined by disc difusion and MIC methods. PCR-sequencing was performed to assess nalD gene mutations in ciprofloxacin resistant strains. Seventeen from 45 isolates of P.aeruginosa were ciprofloxacin resistant (MIC≥1024 µg/ml). PCR-sequencing analysis showed that one resistant isolate had one- C nucleotide deletion in codon 193 (p.Leu193CysfsX, in gene level: c.577delC)) (c.577delC) and three resistant isolates had L153Q missense mutations in nalD gene. It appears that mutations of nalD gene lead to overexpression of mexAB-oprM and subsequently ciprofloxacin resistance in P.aeruginosa isolates in Guilan province