Purpose: We evaluated different virulence factors and pathogenicity of Vibrio anguillarum and Vibrio parahaemoliticus in the greater wax moth Galleria mellonella animal model.
Methods: Eight strains of V. anguillarum, the causative agent of vibriosis in fish, and thirty strains of the seafood-borne human pathogen, V. parahaemoliticus, were evaluated. Wild-type and mutant strains of virulence genes: vah1 and rtxA (V. anguillarum) and pilA, mshA and gbpA (V.parahaemolyticus) were also tested in Galleria model. Larvae were inoculated with individual Vibrio strains at concentrations of 106, 105, and 104 CFU/larva, monitored for mortality, (LT50 - time taken to kill 50% of insects), and for phenotype changes over seven days at 20°C.
Results: Differences in mortality were dose-dependent. Comparison between Vibrio spp. suggests a higher virulence associated with V. parahaemolyticus strains; an LT50 of 24 hours (dose of 106 CFU/larva) was observed for the majority of tested strains. LT50 of 48 hours was recorded for only three out of eight V. anguillarum strains. Insertions and in-frame deletion of vah1 and rtxA genes of V. anguillarum resulted in reduced mortality in larvae. Natural isolates of V. parahaemolyticus from oysters, water, and planktons demonstrated higher virulence than clinical isolates, especially at the lower doses. The difference was strain-related and not statistically significant. The virulence of the wild-type V. parahaemolyticus measured by LT50 did not significantly differ from the isogenic pilA, mshA and gbpA deletion mutants at the 106 CFU/larva. At the lower doses, virulence of the wild-type strain was significantly (P˂0.05) higher from D pilA and D gbpA, while D mshA did not differ.
Significance: Comparison between Vibrio spp. suggests a higher virulence potential associated with V. parahaemolyticus strains relative to V. anguillarum strains.