Genotyping and diversity of virulence genes among Shigella sonnei isolated from children with diarrhoea

Abstract

Shigella sonnei, which has historically prevailed in industrialized countries, is currently undergoing an unprecedented expansion throughout the developing world. The harshness of shigellosis relies on certain virulence factors produced by the pathogen. Available information regarding virulence genes and epidemiological relatedness of S. sonnei strains in Iran is relatively scarce. In this study, 3540 stool specimens were obtained from children with diarrhoea in Tehran, Iran, from September 2016 through January 2018. PCR assays were performed to evaluate the presence of virulence genes among S. sonnei strains. The genetic relatedness of these strains was also assessed by multiple-locus variable number tandem repeat (VNTR) analysis (MLVA). A total of 50 S. sonnei strains were obtained, all of which harboured ipaH, sigA, and virA, whereas ial, invE, and sen were positive in 70% (n = 35), 62% (n = 31), and 54% (n = 27) of the strains, respectively. None of the S. sonnei strains carried set1A, set1B, and sat. The most frequent virulence profile was VP1 (positive for ipaH, ial, invE, sen, sigA, and virA), which was observed in 16 (32%) strains. Using MLVA, 12 genotypes were identified. According to the minimum spanning tree (MST) analysis, S. sonnei strains were grouped into three clonal complexes. CC1, which consisted of 44 (88%) isolates, was the largest clonal complex identified. No association was observed between virulence profiles and genotypes. Overall, it was shown that S. sonnei strains were virulent and clonally related. Furthermore, MLVA can be used as a helpful method for epidemiological investigations.