The Role of parC, parE, and qnrB Genes in Ciprofloxacin-Resistant Escherichia coli Isolates from Urinary Tract Infections

Urinary tract infections (UTIs) are the most common infectious diseases, imposing great costs on the community. Escherichia coli (E. coli) is the most frequent pathogen of UTIs. On the other hand, ciprofloxacin is a wide-spectrum antibiotic, used for the treatment of persistent and recurrent UTIs. Nevertheless, the increasing chromosomal or plasmid resistance of this bacterium has become a major health problem. In this study, we aimed to determine the role of parC, parE, and qnrB genes in ciprofloxacin-resistant E. coli isolates from urine samples of patients suffering from UTI.
Midstream urine samples of patients suffering from UTIs, who were referred to Imam Khomeini hospital, Tehran, Iran during May-October 2014, were collected and evaluated for E. coli isolates. All the isolates were subjected to antimicrobial susceptibility testing (AST) by the standard disk diffusion method, according to the clinical and laboratory standards institute (CLSI) 2014 guidelines. The role of chromosomal genes, parC and parE, in addition to plasmid gene qnrB, was determined by polymerase chain reaction (PCR) method and further sequencing.
Among 124 patients, 64.5% of UTI cases were positive for E. coli. Based on the AST results, 77.5% of the isolates were resistant to ciprofloxacin. The size of PCR bands was 265 bp for parE, 389 bp for parC, and 268 bp for qnrB genes. Also, the frequency of intact genes among ciprofloxacin–resistant isolates was 90.9% for parC, 97.67% for parE, and 0% for qnrB genes. Some mutations were detected in the chromosomal genes after sequence analysis.
This study showed the important role of mutated chromosomal resistant genes in comparison with plasmid genes in the emergence of ciprofloxacin-resistant E. coli strains.