Enhancement of host resistance to microbial infections in mice fed a high fat diet by Lactobacillus casei cells.

The carbon clearance ability of female ddY mice was markedly reduced by feeding with a high fat-low carbohydrate (HFLC) diet for 8 weeks. The reduced clearance ability was restored by a single intraperiotoneal (i.p.) injection with heat-killed Lactobacillus casei (YIT 9018) cells (LC 9018). The i.p. injection of LC 9018 into the HFLC diet-fed mice led to a remarkable enhancement of nonspecific resistance when they were exposed to 50% lethal doses of Pseudomonas aeruginosa or herpes simplex virus, type 1. The resistance-enhancing capacity of LC 9018 against P. aeruginosa infection was significantly maintained for 7 days after the ip inoculation with LC 9018 in mice fed the HFLC diet. The reduced in vivo killing activity of peritoneal exudate cells (macrophage-rich) from mice fed the HFLC diet to P. aeruginosa infection was markedly augmented by the i.p. administration of LC 9018. The results indicate that LC 9018, one of the bacterial immunostimulants, may restore the reduced host defense functions in mice induced by feeding with a high fat diet for a long period.