In vivo screening platform for shiga toxin-producing Escherichia coli (STEC) using Caenorhabditis elegans as a model

Shiga toxin-producing Escherichia coli (STEC) strains are the main cause of bacillary dysentery, although STEC strains generally induce milder disease symptoms compared to Shigella species. This study aimed to determine the virulence of STEC using the nematode Caenorhabditis elegans as a model host. Worm killing, fertility and bacterial colonisation assays were performed to examine the potential difference in the virulence of STEC strains compared to that of the control E. coli OP50 strains on which worms were fed. A statistically significant difference in the survival rates of C. elegans was observed in that the STEC strains caused death in 8-10 days and the E. coli OP50 strains caused death in 15 days. STEC strains severely reduced the fertility of the worms. The intestinal load of bacteria in the adult stage nematodes harbouring the E. coli OP50 strains was found to be 3.5 log CFU mL-1. In contrast, the STEC strains E15, E18 and E22 harboured 4.1, 4.2 and 4.7 log CFU ml-1 per nematode, respectively. The heat-killed STEC strains significantly increased the longevity of the worms compared to the non-heated STEC strains. In addition, PCR-based genomic profiling of shiga toxin genes, viz., stx1 and stx2, identified in selected STEC strains revealed that these toxins may be associated with the virulence of the STEC strains. This study demonstrated that C. elegans is an effective model to examine and compare the pathogenicity and virulence variation of STEC strains to that of E. coli OP50 strains.