Administration of Lactiplantibacillus brownii Strain MH-1 During the Larval Stage Increases the Resistance Against Staphylococcus aureus subsp. aureus in Caenorhabditis elegans

Lactiplantibacillus brownii is a new species of lactic acid bacteria discovered in sauerkraut in Russia, first reported in 2023. We previously isolated L. brownii strain MH-1 (MH-1) from homemade pickled Chinese cabbage in Japan and reported that MH-1 prolonged healthspan and improved stress resistance in Caenorhabditis elegans. In the present study, we investigated the effect of feeding MH-1 on resistance to infections in C. elegans. MH-1 failed to increase its resistance to infection with Staphylococcus aureus subsp. aureus (SA) and Salmonella enterica (SE) at the adult stage. However, MH-1 feeding at the larval stage remarkably increased the survival rate of worms infected with SA, but not with SE. Genes related to the innate immune response were significantly upregulated by MH-1 feeding at the larval stage compared with those of the control group. A survival assay using loss-of-function mutants revealed that resistance to SA infection conferred by MH-1 feeding during the larval stage requires daf-16 and pmk-1. These results suggest that MH-1 feeding at the larval stage likely confers resistance to SA infection by enhancing host immunity via the insulin/insulin-like growth factor 1 signaling and p38 mitogen-activated protein kinase pathways.