The Mutations of Topoisomerase Genes and Their Effect on Resistance to Fluoroquinolones in Extended-Spectrum β-Lactamase-Producing Escherichia coli

Fluoroquinolones have been used for empirical treatment of urinary tract infections in recent years. This study aimed at identifying mutations in gyrA and parC genes and their correlation with fluoroquinolone minimal inhibitory concentration (MIC) among extended-spectrum β-lactamase-producing (ESBL) Escherichia coli.
A total of 240 E. coli were isolated from urine of patients during 2014 and 2015 in the west of Iran. The isolates were screened for ESBL-producing phenotype using combined disc diffusion test. The susceptibility of ESBL isolates to ciprofloxacin and levofloxacin was determined by disk diffusion and microdilution assay. PCR, sequencing and bioinformatics analysis were performed to identify mutations in gyrA and parC genes.
Of 240 isolates, 66 (27.5%) were ESBL positive. Of them, 45 (68.1%) isolates were resistant to both ciprofloxacin and levofloxacin. Sequence analysis showed mutations in the quinolone resistance determining region (QRDR) in the 2 codons (Ser-83, Asp-87) of gyrA and 2 codons (Ser-80, Glu-84) of parC. One mutation at codon of Ala-192 was found outside the QRDR in parC.
Isolates with mutations in QRDR of parC and gyrA had the higher MIC level compared to isolates with mutations only in gyrA. The highest level of resistance was detected in isolates with accumulation of mutations in gyrA and parC. A high frequency of fluoroquinolone resistance among ESBL producing E. coli isolates indicated the clustered transmission of resistance genes in this bacterium. A new mutation outside the QRDR of parC was detected, which may play a role in fluoroquinolone resistance.