Lipopolysaccharide O-antigen of enterohemorrhagic Escherichia coli O157:H7 is required for killing both insects and mammals

Abstract

Studies of enterohemorrhagic Escherichia coli (EHEC) infection mechanisms using mammals require large numbers of animals and are both costly and associated with ethical problems. Here, we evaluated the pathogenic mechanisms of EHEC in the silkworm model. Injection of a clinically isolated EHEC O157:H7 Sakai into either the silkworm hemolymph or intraperitoneal fluid of mice killed the host animals. EHEC O157:H7 Sakai deletion mutants of the rfbE gene, which encodes perosamine synthetase, a monosaccharide component synthetase of the O-antigen, or deletion mutants of the waaL gene, which encodes O-antigen ligase against the lipid A-core region of lipopolysaccharide (LPS), had attenuated killing ability in both silkworms and mice. Introduction of the rfbE gene or the waaL gene into the respective mutants restored the killing ability in silkworms. Growth of both mutants was inhibited by a major antimicrobial peptide in the silkworm hemolymph, moricin. The viability of both mutants was decreased in swine serum. The bactericidal effect of swine serum against both mutants was inactivated by heat treatment. These findings suggest that the LPS O-antigen of EHEC O157:H7 plays an important defensive role against antimicrobial factors in the host body fluid and is thus essential to the lethal effects of EHEC in animals.

Intestinal microbes influence the survival, reproduction and protein profile of Trichinella spiralis in vitro

“…This study investigated, for the first known time, the effects of gastrointestinal microbes on vitality, reproduction and survival of T. spiralis, and the analysis of responding genes/proteins in T. spiralis after co-cultures with the different bacterial strains. The results indicated T. spiralis failed to thrive and reproduce well in the presence of harmful bacteria such as EHEC and S. enterica, which is supported by the outcomes of a recent investigation that showed EHEC can infect and kill C. elegans, insects and mammals by Lipopolysaccharide (LPS) (Miyashita et al, 2012;Youn et al, 2013). In addition, a recombinant attenuated Salmonella vaccine that protects mice against the parasite has also been reported (Konjufca et al, 2006).…”

The role for TolA in enterohemorrhagic Escherichia coli pathogenesis and virulence gene transcription

“…Larvae were injected with 1 Â 10 5 CFU of each strain, the concentration of which represents the LD 50 as determined by injecting larvae with 10-fold dilutions (from 10 2 to 10 6 CFU) of wild-type strain TW14359. In the silkworm model, a separate insect model for bacterial pathogenesis [70], LPS production was shown to play a significant role in the virulence of EHEC [71]. As tolA mutants are predicted to be defective in O-antigen polymerization and localization to the outer membrane [72], it was hypothesized that decreased EHEC virulence observed in G. mellonella would similarly result from a deficiency in LPS production.…”

Two-spotted cricket as an animal infection model of human pathogenic fungi

“…The nematode C. elegans and the fruit fly D. melanogaster cannot survive at 37°C. Silkworms and the greater wax moth larva can be used as animal infection models at 37°C (25)(26)(27), but their infection sensitivities to fungi are drastically increased at 37°C compared to that at a lower temperature (19,(28)(29)(30)(31). The increased infection sensitivity of these insects at 37°C is considered to be due to damage to the immune system at a high temperature (32)(33)(34).…”