Human pathogenic Yersinia spp. can colonize Steinernema entomopathogenic nematodes

The existence of biological micro-reservoirs explaining the long-term survival of pathogenic bacteria in the environment has long been speculated. Soil invertebrates in particular are suspected to act as intermediary hosts for such pathogenic bacteria and entomopathogenic nematodes (EPNs) were investigated in this respect. To determine whether human pathogenic Yersiniae are able to colonize and multiply in EPNs, a laboratory model was developed. This model consists in Galleria mellonella insect larvae, Steinernema EPNs carrying or not their natural Xenorhabdus symbiont and Yersiniae, brought artificially either in the gut of EPNs or in the haemocoele of the insect larva prior to infection. Using a single direct injection in the insect haemolymph, Y. pseudotuberculosis was recovered from nematodes after seven consecutive EPN infection cycles. As compared to other pathogenic Yersiniae as well as other pathogenic enterobacteria, Y. pseudotuberculosis demonstrated much higher ability to colonize Steinernema EPNs. Genetic determinants potentially involved in the colonization of Steinernema nematodes were knocked out and the resulting Y. pseudotuberculosis mutants were complemented with the corresponding intact genes borne on a low copy plasmid. The EPN colonization capacity of the knockout mutants could not be fully characterized for technical and timing reasons. Nevertheless, our results globally demonstrate long-term persistence of Y. pseudotuberculosis in EPNs in our laboratory conditions. Finally, a method for swapping fluorescent labels in tagged bacteria was developed and used to re-engineer fluorescently labelled Y. pseudotuberculosis. Dual fluorescence confocal microscopic observations showed that the tagged Yersinia colonized distinct Steinernema tissues as compared to the natural Xenorhabdus symbiont of this nematode.(SC - Sciences) -- UCL, 201