Exploring the impact of probiotic route of administration on its protective effects against pathogenic infection in Galleria mellonella

Identifying promising probiotic candidates for further development remains challenging. Traditional mammalian models are invaluable for assessing efficacy, but the associated limitations slow the preliminary screening process. The Galleria mellonella larvae have emerged as a powerful in vivo screening model. Most probiotic studies on G. mellonella use intra-hemocelic injection, bypassing the natural gut entry point, making it analogous to introducing probiotics into the mammalian blood. Therefore, 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 the commonly studied intra-hemocelic injection and the less common oral administration of a probiotic, Escherichia coli Nissle 1917 (EcN1917), on its protective efficacy against a gastrointestinal pathogen, Salmonella Typhimurium ATCC 14028 (ST14028). 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, concluding that the route of probiotic administration in G. mellonella significantly impacts the protective effects of probiotics.