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 β-lactamases (blaTEM, blaSHV, blaCTX-M, blaOXA, blaPER, blaVEB, blaGES and blaCMY), carbapenemases (blaKPC, blaNDM and blaIMP), 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 β-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.