Quinolone Resistance Determinants qnr, qep, and aac(6')-Ib-cr in Extended-Spectrum Β-Lactamase Producing Escherichia coli Isolated From Urinary Tract Infections in Tehran, Iran

Prevalence of plasmid mediated quinolone resistance in Escherichia coli clinical isolates is a serious problem in developing countries.
The aim of this study was to investigate quinolone resistance determinants among Extended-Spectrum Β-Lactamases (ESBL)-producing E. coli recovered from patients with nosocomial urinary tract infection.
A total of 290 E. coli isolates, obtained from patients with UTI, were included in this study. The phenotypic confirmatory test for ESBL production was performed by double disc synergy test and combined disk diffusion test. Kirby-Bauer Disk diffusion method was performed to test susceptibilities of ESBL-producing E. coli isolates to 15 antimicrobial agents. Isolates were screened for the presence of ESBL and plasmid-mediated quinolone resistance genes by polymerase chain reaction (PCR).
In the present study, 290 (71.7%) E. coli strains were recovered from 410 hospitalized patients with UTI, 51.7% of which were found to have ESBL positive results. In vitro, the susceptibilities of ESBL-producing E. coli strains showed that all isolates were resistant to amoxicillin and penicillin and resistance rates to other of antibiotics differed from 40% to 96%. Among the 150 ESBL positive isolates, frequencies of aac(6’)-Ib, oqxA, oqxB, qnrA, qnrB, qnrS, and qepA were 74.7%, 8%, 4%, 3.3%, 1.3%, 2%, and 2.7%, respectively. Coexistence of bla CTX-M, bla TEM, bla CTX-M, and aac(6’)-Ib were the most widely distributed resistance genotypes.
The data of the present study revealed the high prevalence of plasmid-mediated quinolone resistance genes among ESBL-producing E. coli in the hospitals. The bla CTX-M genes were found to be the dominant ESBL-encoding gene.