Exploring the Impact of Probiotic Route of Administration on Its Protective Effects against Pathogenic Infection in Galleria mellonella

In probiotic research, identifying promising candidates for further development remains challenging. Traditional mammalian models are invaluable for assessing efficacy, but limitations such as high cost, ethical considerations, and lengthy reproductive cycles can slow the preliminary screening process. The Galleria mellonella larvae have emerged as a powerful in vivo-like screening model. Most studies on G. mellonella often use intra-hemocelic injection, bypassing the natural gut entry point for probiotics, which is analogous to introducing probiotics into the mammalian blood. Despite their advantages, discrepancies exist between G. mellonella and mammalian models, particularly regarding the route of probiotic administration. This study bridges this gap by investigating the differential effects of oral and intra-hemocelic administration of a probiotic, Escherichia coli Nissle 1917 (EcN1917), on its protective efficacy against a gastrointestinal pathogen, Salmonella Typhimurium ATCC 14028 (ST14028). The larvae were challenged with varying doses of EcN1917 and ST14028 through both routes. Survivability, health index, and bacterial burden in the gut and hemolymph were assessed. This study demonstrated that oral EcN1917 pre-treatment significantly increased survivability against ST14028 infection compared to the control group and alleviated the pathogen gut burden. Notably, injection pre-treatment decreased survivability. This discrepancy is attributed to the dual nature of probiotics, exhibiting beneficial effects in the gut but acting as pathogens in non-native locations like the hemolymph. This study concludes that the route of probiotic administration in G. mellonella significantly impacts the protective effects of probiotics.