Plasmid-mediated quinolone resistance in Shigella sonnei and Shigella flexneri isolated from pediatric diarrheal

Introduction: Fluoroquinolones are one of the most common antibiotics in the treatment of Shigella infections worldwide. The presence of plasmids carrying quinolone-resistance genes is one of the most important mechanisms for resistance to these drugs. Therefore, the aim of this study was to determine the presence of quinolone resistance plasmid genes (qnr) in Shigella sonnei and Shigella flexneri isolated from pediatric diarrhea. Material and methods: In a 10-month period from the beginning of June to the end of March 2012, 91 isolates of Shigella were obtained from 358 non-repetitive diarrhea samples. After identification and confirmation of Shigella isolates, antibiotic susceptibility test was performed based on the CLSI instruction. The molecular PCR test was performed to amplify qnrA, qnrB, qnrC, qnrD and qnrS genes. Results: Slide agglutination test showed that the prevalence of Shigella sonnei and Shigella flexneri were 69.2% and 30.8%, respectively. The disc diffusion test showed that all Shigella flexneri were susceptible to levofloxacin. Most of the Shigella sonnei were resistant to Streptomycin. The frequency of qnrA, qnrB and qnrS genes were 26.4%, 74.7% and 46.2%, respectively. All strains were negative for the presence of qnrC and qnrD genes. Conclusions: The qnrB gene is the most common plasmid-mediated quinolone resistance (PMQR) in our treatment centers. Because of their plasmid origin, these genes have the ability to transfer and have high ability to spread to the other isolates. Since the change in pattern of antibiotic susceptibility is occurs, perform of antibiotic susceptibility test necessary.