Antimicrobial susceptibility patterns and molecular characterization of plasmid-mediated quinolone resistance determinants among Salmonella and Shigella spp. isolated from pediatric patients

Abstract

Background: Diarrhea remains a serious public health problem, which could be life- threatening in children. Salmonella and Shigella are among the main responsible agents. Fluoroquinolones are the most common antibiotics prescribed to treat these infections; however, increasing rate of resistance and its spread through plasmid- mediated quinolone resistance (PMQR) genes should be considered for medication in each country. To achieve this aim, the current study was conducted to determine the frequency of PMQR genes in Shigella and Salmonella isolates of pediatric patients with acute diarrhea. Methods: In this study, Shigella and Salmonella isolates from fresh stool samples of diarrhea patients were included from May 2017 to May 2018. All the isolates were characterized by conventional phenotypic and molecular methods. The antibiotic resistance profiles and the frequency of PMQR genes were determined by standard susceptibility and molecular test methods. Results: The highest antibiotic resistance rate among Shigella and Salmonella isolates was related to trimethoprim-sulfamethoxazole (37/40; 92.5%) and cefoxitin (5/45; 11.1%), respectively. Although qnrS, qepA, and aac (6¢)-Ib-cr genes were characterized in 32.5%, 2.5%, and 2.5% of the Shigella strains, qepA (17.7%) and qnrS (4.4%) were among the common PMQR determinants in the Salmonella isolates, respectively. The reduced susceptibility to ciprofloxacin was detected among 25% and 22.2% of PMQR-harboring strains of Shigella and Salmonella, respectively. Conclusion: Low rates of ciprofloxacin resistance and low frequency of MDR Salmonella and Shigella isolates were characterized in this study. Most of the isolates that carried PMQR determinants presented only low-level resistance and reduced susceptibility to ciprofloxacin.