Determination of virulence of L. monocytogenes strains of environmental and food sources using an invertebrate model

The virulence potential of 9 L. monocytogenes strains isolated from food products at different stages of the fresh produce supply chain and a food processing facility was determined using G. mellonella. Strains were used to infect G. mellonella larvae through the haemocoel with a dose of 106 CFU, which were then compared to a L. monocytogenes reference EGD-e and also L. ivanovii. Virulence was assessed by evaluating mortality rates, larvae health index score (HIS), counting viable bacteria in larvae, and the larval immunological response to infection. Significant differences in ability to cause larval mortality were observed between strains. L. monocytogenes strains NLmo4 and NLmo5 caused the most mortality rates, 98.8% and 96.7%, respectively, at 7 d after infection, whilst NLmo20 induced a mortality rate of 65% at the same time point, significantly differing from NLmo4&5 (p