Antimicrobial susceptibility and virulence gene analysis of Shigella species causing dysentery in Iranian children: Implications for fluroquinolone resistance.

Shigella species significantly impact global health due to their role in diarrheal diseases. A 2019-2022 cross-sectional study on 432 stool samples from pediatric patients in Mashhad, Iran, identified Shigella spp. and tested their susceptibility to 12 antimicrobials by the disk diffusion method. The presence of virulence factors, namely ipaH, virA, stx1, and stx2, as well as plasmid-mediated quinolone resistance (PMQR) genes, including qnrA, qnrB, qnrC, qnrD, and qnrS, were ascertained through the utilization of polymerase chain reaction techniques. Sequencing of 15 isolates detected mutations within quinolone resistance-determining regions (QRDRs) at the gyrA and parC genes, indicating fluoroquinolone (FQ) resistance. 19.2 % (83/432) of stool samples contained Shigella, primarily S. sonnei (77.1 %), followed by S. flexneri (21.6 %) and S. boydii (1.2 %). Most isolates were from children under five (55.4 %). All strains had the ipaH gene, lacked stx1 and stx2, and 86.7 % had virA. High resistance was noted for ampicillin and tetracycline (84.3 % each), trimethoprim-sulfamethoxazole (81.9 %), and azithromycin (60.2 %). 87.1 % of isolates were multidrug-resistant (MDR). The most common PMQR genes were qnrA and qnrS (41 % each). The qnrD gene, prevalent in 36.1 % of cases, is reported in Iran for the first time. The most common PMQR profile was qnrADS (15.7 %). Resistance to nalidixic acid and ciprofloxacin was 45.8 % and 12 %, respectively. The Shigella isolates exhibited mutations in the gyrA (at codons 83, 87, and 211) and parC (at codons 80, 84, 93, 126, 128, 129, and 132) genes. The D87Y mutation in the gyrA gene was the most common in Shigella isolates, occurring in 73 % of cases. The F93S and L132T mutations in the parC gene were unique to this study. Empirical FQ therapy in patients infected with MDR Shigella, possessing PMQR determinants and/or mutations in the QRDRs of gyrA and parC, may escalate the risks of secondary diseases, extended treatment duration, therapeutic failure, and resistance spread. Consequently, the necessity for continuous surveillance and genetic testing to detect FQ-resistant Shigella strains is of paramount importance.