Prevalence of Resistance to Quinolone and Fluoroquinolone Antibiotics and Screening of qnr Genes Among Escherichia coli Isolates From Urinary Tract Infection

Antibiotic resistance (AR) is an important challenge in prevention, treatment and control of infectious diseases and is a public health threat for human. Escherichia coli strains are the major causes of urinary tract infections (UTIs).
This research aimed to determine prevalence of resistance to quinolone and fluoroquinolone antibiotics and screen qnr genes among E. coli isolates from UTIs.
A total of 105 E. coli isolates were obtained from UTI cases in Bojnord city (northeast of Iran) and confirmed by biochemical tests. All strains were studied to determine their resistance to 3 antibiotics including ciprofloxacin, nalidixic acid, and levofloxacin via disk diffusion method. Moreover, the frequency of qnrA, qnrB and qnrS genes and phylogroups was studied by conventional Polymerase chain reaction (PCR).
In this study, prevalence of phenotypic AR to ciprofloxacin, nalidixic acid and levofloxacin was 47.6%, 44.8% and 38.1%, respectively. Three isolates were positive for qnrS and 1 isolate was positive for qnrA. Seven phylogenetic groups were also identified as follows: 18% A0, 6.7% A1, 7.6% B1, 1.9% B22, 23.8% B23, 15.3% D1 and 26.7% D2.
Prevalence of qnr genes was very low; thus, other types of qnr and plasmid-mediated quinolone resistance genes were probably responsible for the resistance. Phenotypic AR to the 3 antibiotics was found in approximately half of E. coli strains. It is strongly recommended that antibiogram tests should be done before prescribing the ciprofloxacin, nalidixic acid and levofloxacin for UTIs.