Distribution of antimicrobial resistance genes and integrons among Shigella spp. isolated from water sources

Objectives: Shigella spp. are an important group of waterborne pathogens worldwide. This study aimed to determine the frequency of Shigella spp. in a large collection of water samples and to uncover molecular aspects of antimicrobial resistance in the recovered isolates. Methods: The antimicrobial resistance patterns, antimicrobial resistance genes (ARGs), including beta-lactamases (bla(TEM), bla(SHV), bla(CTX-M), bla(OXA), bla(PER), bla(VEB), bla(GES) and bla(CMY)), carbapenemases (bla(KPC), bla(NDM) and bla(IMP)), plasmid-mediated quinolone resistance (PMQR) genes [qnrA, qnrB, qnrS and aac(6')-Ib] and tetracycline resistance genes [tet(A), tet(B), tet(C) and tet(D)], as well as class 1 and 2 integrons were analysed in Shigella spp. isolated from different water sources in Iran. Results: Of 788 tested samples, Shigella sonnei and Shigella flexneri were detected in 9 (1.1%) and 6 (0.8%) samples, respectively. A multidrug-resistant (MDR) phenotype was observed in all of the isolates. Among the 15 Shigella isolates, 12 (80.0%), 5 (33.3%) and 7 (46.7%) were positive for genes encoding beta-lactam resistance, PMQR and tetracycline resistance, respectively. Class 1 integrons were more frequently detected among the isolates (8/15; 53.3%), consisting of 7 isolates (87.5%) with dfrA17-aadA5 and 1 isolate (12.5%) with sat1-aadA1 gene cassettes. The class 2 integron was detected in 3 isolates (20.0%) with the classic gene cassette array dfrA1-sat2-aadA1. Conclusions: Overall, this study showed that Shigella spp. are prevalent in water sources in Iran. Furthermore, the potential role of ARGs and integrons in the emergence of a MDR phenotype in Shigella isolates of water origin was demonstrated. (C) 2019 Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.