A Survey of gyrA Target-Site Mutation and qnr Genes among Clinical Isolates of Escherichia coli in the North of Iran

Urinary tract infection (UTIs) caused by Escherichia coli is one of the most common human complications. The discriminate use of antibiotics leads to increasing multiple-drug resistance (MDR) in E. coli.

This study aimed at investigating the frequency of fluoroquinolones resistance by detecting qnr genes and mutation in gyrA gene in clinical isolates of E. coli in the North of Iran.

This cross-sectional study was conducted on 309 E. coli isolates collected from major hospitals in Rasht, North of Iran. All isolates were identified by standard microbiological methods. Antimicrobial susceptibility testing was conducted by the disk diffusion method for the three quinolone antibiotics. The detection of gyrA, qnrS, qnrB, and qnrA genes was performed by the polymerase chain reaction (PCR) method. PCR products of gyrA gene were digested by HinfI enzyme to identify the mutation in gyrA gene by restriction fragment length polymorphism (RFLP) method.

Of 309 tested E. coli isolates, the most common resistance was observed against nalidixic acid (60.2%) and the least common one against norfloxacin (40.5%). The prevalence of qnrS, qnrB, and qnrA genes was 4.5%, 73.1%, and 62.8%, respectively. Mutation in gyrA gene was observed in codon 83 in 56.3% of the strains.

In summary, despite the significant association of the investigated genes with fluoroquinolones resistance in these bacteria, the presence of these genes in susceptible strains suggested that some other possible mechanisms may also influence resistance against fluoroquinolones