Low distribution of genes encoding virulence factors in Shigella flexneri serotypes 1b clinical isolates from eastern Chinese populations

Background The ability of Shigella to invade, colonize, and eventually kill host cells is influenced by many virulence factors. However, there is no analysis of related genes in Jiangsu Province of China so far. Shigella flexneri was collected from 13 cities of Jiangsu Province through the provincial Centers for Disease Control (CDC) for analysis of distribution of major virulence genes (ipaH, ipaBCD, ial, virF, virB, sigA, set1A, sepA, sat, pic, set1B and sen) detected by PCR technology. Results A total of 545 isolates received were confirmed as S. flexneri which belongs to 11 serotypes of S. flexneri, among which serotype 2a was the most predominant (n = 223, 40.9%). All isolates were positive for ipaH gene, followed by sat (94.1%), sigA (78.9%), set1B (78.0%), pic (77.6%), set1A (74.5%), virF (64.8%), sepA (63.5%), sen (56.9%), ipaBCD (50.5%), ial (47.0%) and virB (47.0%). The presence of virulence genes in different serotypes was distinct. The existence of virulence genes of serotype 1b was generally lower than other serotype-the positive rate for virulence genes was between 0.0 and 14.1% except for ipaH and sat. In addition, virulence genes also fluctuated in different regions and at different times in Jiangsu province. The result of analysis on the relationship between virulence genes of S. flexneri showed that the existence of virulence genes of Shigella could be well represented by multiplex PCR combination ipaH + ial + set1A, which had a high clinical value. Conclusions The present study was designed to explore the prevalence of 12 S. flexneri-associated virulence genes. The data showed high diversity of virulence genes with regard to periods, regions and serotypes in Jiangsu Province of China.