Determination of gyrA and parC mutations and prevalence of plasmid-mediated quinolone resistance genes in Escherichia coli and Klebsiella pneumoniae isolated from patients with urinary tract infection in Iran.

OBJECTIVES: Fluoroquinolones (FQs) are recommended as the drugs of choice for the empirical treatment of urinary tract infections (UTIs). This study investigated the molecular determinants of FQ resistance in Escherichia coli and Klebsiella pneumoniae isolates in Iran.

METHODS: A total of 364 clinical isolates of E. coli (n=144) and K. pneumoniae (n=220) were collected from patients with UTI. Susceptibility of the isolates to ciprofloxacin, levofloxacin, gatifloxacin and nalidixic acid was evaluated by disk diffusion. The presence of qnrA, qnrB and qnrS genes was assessed by PCR. Nucleotide sequences of the gyrA and parC genes were determined.

RESULTS: Eighty-seven (60.4%) and 15 (6.8%) E. coli and K. pneumoniae isolates, respectively, were resistant to at least one of the tested FQs. Plasmid-mediated quinolone resistance (PMQR) genes were detected in 12.6% and 60.0% of FQ-resistant E. coli and K. pneumoniae, respectively. Whilst qnrB predominated in K. pneumoniae, qnrS was the most prevalent PMQR gene in E. coli. S83L (98.9%) and D87N (59.8%) were the most frequent mutations identified in GyrA of E. coli, and 55.2% (n=48) of FQ-resistant E. coli isolates had mutation in ParC harbouring S80I and E84V substitutions. The GyrAS83L substitution was found in only one FQ-resistant K. pneumoniae isolate.

CONCLUSIONS: FQ resistance was much more common in E. coli isolates than in K. pneumoniae. Whilst mutations in the drug target-encoding genes gyrA and parC were the major mechanisms involved in FQ resistance in E. coli, PMQR determinants commonly mediated FQ resistance in K. pneumoniae.