Escherichia coli O157:H7 LPS O-side chains and pO157 are required for killing Caenorhabditis elegans

•C. elegans fed on EHEC O157:H7 wild-type or mutant strains.•Mutants lacking either pO157 or LPS O-side chains caused full attenuation in killing C. elegans.•The LPS O-side chain-defective mutant strain could not colonize in the intestine of C. elegans.•pO157 and PerA are required for EHEC O157:H7 to kill C. elegans. As a model host, the nematode Caenorhabditis elegans has been used for studying unknown pathogen–host interactions and identifying novel virulence factors in bacterial pathogens. Among the bacterial pathogens that can induce death of C. elegans is enterohemorrhagic Escherichia coli (EHEC) O157:H7, a major serotype of EHEC that causes hemorrhagic colitis and hemolytic uremic syndrome in humans and animals. However, it is unknown which EHEC O157:H7 factors are required for nematode death. In this study, bacterial ability to kill C. elegans was tested for several EHEC O157:H7 wild-type and mutant strains missing one virulence-associated factor, including Shiga toxins, enterohemolysin, pO157 (a large virulence plasmid in EHEC O157:H7), Type 3 secretion system, LuxS, and lipopolysaccharide (LPS) O-side chains. Our results demonstrate that only mutants lacking either pO157 or LPS O-side chains cause full attenuation in killing C. elegans. The LPS O-side chain-defective ΔperA mutant strain was not able to colonize in the intestine even at 24h post-feeding with C. elegans, while the wild-type strain began to accumulate and colonize in the intestine as early as 3h post-feeding. A simple complementation of the mutant strain with the plasmid carrying the intact perA gene in trans completely restored the production of LPS O-side chains, as well as the ability to kill C. elegans. Our results show that pO157 and PerA are required for EHEC O157:H7 to kill C. elegans.