| Summary: | The invasiveness properties of Shigatoxigenic and enteropathogenic <i>Escherichia coli</i> (STEC and EPEC) O80:H2 in humans and calves are encoded by genes located on a pS88-like ColV conjugative plasmid. The main objectives of this study in larvae of the <i>Galleria mellonella</i> moth were therefore to compare the virulence of eight bovine STEC and EPEC O80:H2, of two <i>E. coli</i> pS88 plasmid transconjugant and STX2d phage transductant K12 DH10B, of four <i>E. coli</i> O80:non-H2, and of the laboratory <i>E. coli</i> K12 DH10B strains. Thirty larvae per strain were inoculated in the last proleg with 10 μL of tenfold dilutions of each bacterial culture corresponding to 10 to 10<sup>6</sup> colony-forming units (CFUs). The larvae were kept at 37 °C and their mortality rate was followed daily for four days. The main results were that: (i) not only the STEC and EPEC O80:H2, but also different <i>E. coli</i> O80:non-H2 were lethal for the larvae at high concentrations (from 10<sup>4</sup> to 10<sup>6</sup> CFU) with some variation according to the strain; (ii) the Stx2d toxin and partially the pS88 plasmid were responsible for the lethality caused by the <i>E. coli</i> O80:H2; (iii) the virulence factors of <i>E. coli</i> O80:non-H2 were not identified. The general conclusions are that, although the <i>Galleria mellonella</i> larvae represent a useful first-line model to study the virulence of bacterial pathogens, they are more limited in identifying their actual virulence properties.
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