The Molecular Study of Antibiotic Resistance to Quinolones in Salmonella enterica Strains Isolated in Tehran, Iran.

Introduction: Salmonella is known as one of the most important causes of gastrointestinal disease in the world. Quinolones and fluoroquinolones are used successfully in the treatment of salmonellosis particularly for infections that have become resistant to several antibiotics. But non-susceptible isolates to quinolones have been reported in several countries. The data are limited about the prevalence of quinolone-resistant isolates in our country. Therefore, this study investigated the plasmid-mediated quinolone resistance genes in Salmonella enterica isolated in Children's Medical Center in Tehran during 2014-2015.

Methods and materials: Salmonella isolates were isolated and identified using standard microbiological methods. Antibiotic susceptibility testing and screening of Salmonella strains resistant to quinolones were performed according to the CLSI guidelines. The molecular investigation was done using specific primers for detection of qnr genes including: qnrA, qnrB and qnrS, by polymerase chain reaction.

Results: Overall, 92 (66.6%) strains were resistant to nalidixic acid. None of the strains showed resistance to ciprofloxacin. Out of the 92 nalidixic acid resistant strains, 52 (56.52%) harbored qnrS genes, 15 strains (16.30%) had both qnrA and qnrS genes. Two (1.1%) isolates were positive for qnrB gene. Twenty four (26.08%) nalidixic acid resistant isolates did not have any qnr qens.

Conclusion: The results of this study show high prevalence of resistance to nalidixic and qnr genes in Salmonella isolates. Plasmid nature of this type of resistance poses an increased risk of dissemination of quinolone resistance between Salmonella and non-Salmonella isolates circulating in hospitals environments.