Protective effect of lactobacillus casei CRL 431 against salmonella in a mouse model: mechanisms involved

Abstract

Salmonella species are Gram-negative bacilli that constitute the causing agents of several animal and human illnesses. They cause acute or chronic infections that can be local (e.g gastroenteritis produced by non-typhoidal serovars) or systemic (e.g. enteric fever produced by typhoidal serovars). Non-typhoidal serovars produce 93.8 million cases of gastroenteritis worldwide, leading to 155,000 deaths each year. According to a foodborne disease surveillance network data supported by the World Health Organization (2001-2005), Salmonella (S.) Enteritidis was the most common serotype worldwide (65% of the isolates), followed by S. Typhimurium (12%) and S. Newport (4%). Numerous studies have proposed the use of probiotics to improve gut health, especially in the protection against enteropathogens. In this sense, the probiotic strain Lactobacillus (L.). casei CRL 431 showed protective effect against S. Typhimurium in BALB/c mouse model. This chapter reports an update of the main biological and immune mechanisms involved in the protection observed with this probiotic bacterium. The effect of other two lactobacilli strains (L. delbruekii subsp. bulgaricus CRL 423 and L. acidophilus CRL 730), which displayed immunostimulating ability but did not show protective capacity against Salmonella was also added comparing with L. casei CRL431. This comparative analysis was conducted to define some effects on the mucosal immune system that would be desired in a probiotic strain to achieve protection against this particular pathogen. The results showed that L. casei CRL 431 was the only strain with protective effect against Salmonella. The continuous treatment (before and after infection) with this strain improved animal survival, and diminished pathogen counts in liver, spleen and large intestine. L. casei CRL 431 administration increased also the number of IgA(+) cells in lamina propria of the small intestine, as well as total and specific anti-Salmonella s-IgA in intestinal fluids. Increased IgA levels correlated with the increased IL-6 levels observed in the animals that received this probiotic bacterium. The preventive administration of L. casei before the infection stimulated the phagocytic activity of peritoneal, Peyer’s patches and spleen macrophages. Probiotic administration post infection increased expression and secretion of IFNγ. The probiotic bacterium also attenuated the intestinal inflammation by reducing tissue damage and polymorphonuclear infiltration, and maintaining the levels of the regulatory cytokine IL-10. Although L. acidophilus CRL 730 increased the number of IgA(+) cells, and L. bulgaricus CRL 423 increased phagocytic activity of macrophages, these mechanisms by themself were not enough to confer protection against S. Typhimurium infection in mouse.