BackgroundDiarrheal infections caused by bacterial enteric pathogens including Salmonella, are one of the major causes of childhood morbidity and mortality in developing countries. Probiotics have been shown to influence both innate and adaptive immunity through direct contact with epithelial and immune cells, or by their ability to modify the gut microbiota. Specific probiotic strains have been shown to reduce or prevent Salmonella infection. While probiotics have limited shelf life in liquid products, especially in non-refrigerated conditions, effective heat treated probiotic strains may offer advantages over their live counterparts especially in terms of processing and storage.
Recently, we investigated the ability of heat treated L. johnsonii La1 NCC533 and B. longum NCC2705 to protect C57Bl/6 mice against infection with Salmonella enteritidis. Both heat treated strains were previously shown to be superior to their live counterparts in upregulating the synthesis of antimicrobial peptides β-defensin 1 and 2 in T84 cells. Continuous administration of La1 led to increased amounts of innate immunity markers in the ileum, including myeloperoxidase, iNOS and Reg3β) as well as increased secretion of IgA. These changes were associated with decreased translocation of Salmonella in the ileum, spleen, liver and mesenteric lymph nodes, as well as less systemic inflammation compared to the Salmonella-infected groups of control mice and B. longum treated mice. However, it remains to be studied if the heat-treated La1 is as efficient as the live La1 in vivo, and if the processing of the strain impacts on its capacity to prevent Salmonella infection.