Establishing <i>Galleria mellonella</i> as an invertebrate model for the emerging multi-host pathogen <i>Helcococcus ovis</i>

<i>Helcococcus ovis</i> (<i>H. ovis</i>) can cause disease in a broad range of animal hosts, including humans, and has been described as an emerging bacterial pathogen in bovine metritis, mastitis, and endocarditis. In this study, we developed an infection model that showed <i>H. ovis</i> can proliferate in the hemolymph and induce dose-dependent mortality in the invertebrate model organism <i>Galleria mellonella</i> (<i>G. mellonella</i>). We applied the model and identified <i>H. ovis</i> isolates with attenuated virulence originating from the uterus of a healthy post-partum dairy cow (KG38) and hypervirulent isolates (KG37, KG106) originating from the uterus of cows with metritis. Medium virulence isolates were also isolated (KG36, KG104) from the uterus of cows with metritis. A major advantage of this model is that a clear differentiation in induced mortality between <i>H. ovis</i> isolates was detected in just 48 h, resulting in an effective infection model able to identify virulence differences between <i>H. ovis</i> isolates with a short turnaround time. Histopathology showed <i>G. mellonella</i> employs hemocyte-mediated immune responses to <i>H. ovis</i> infection, which are analogous to the innate immune response in cows. In summary, <i>G. mellonella</i> can be used as an invertebrate infection model for the emerging multi-host pathogen <i>Helcococcus ovis.</i>