Abstract
Probiotics are formulations containing live microorganisms or microbial stimulants that have some beneficial influence on the maintenance of a balanced intestinal microbiota and on the resistance to infections. The search for probiotics to be used in prevention or treatment of enteric infections, as an alternative to antibiotic therapy, has gained significant impulse in the last few years. Several studies have demonstrated the beneficial effects of lactic acid bacteria in controlling infection by intestinal pathogens and in boosting the host's nonspecific immune response. Here, we studied the use of Lactobacillus acidophilus UFV-H2b20, a lactic acid bacterium isolated from a human newborn from Viçosa, Minas Gerais, Brazil, as a probiotic. A suspension containing 10(8) cells of Lactobacillus acidophilus UFV-H2b20 was inoculated into groups of at least five conventional and germfree Swiss mice to determine its capacity to stimulate the host mononuclear phagocytic activity. We demonstrate that this strain can survive the stressing conditions of the intestinal tract in vivo. Moreover, the monoassociation of germfree mice with this strain for seven days improved the host's macrophage phagocytic capacity, as demonstrated by the clearance of a Gram-negative bacterium inoculated intravenously. Monoassociated mice showed an undetectable number of circulating E. coli, while 0.1% of the original inoculum was still present in germfree animals. Mice treated with viable or heat-killed Lactobacillus acidophilus UFV-H2b20 presented similarly improved clearance capacity when compared with germfree controls. In addition, monoassociated mice had twice the amount of Kupffer cells, which are responsible for the clearance of circulating bacteria, compared to germfree controls. These results suggest that the L. acidophilus strain used here stimulates a nonspecific immune response and is a strong candidate to be used as a probiotic.
Highlights
The adverse effect of toxic metabolites from the intestinal microbiota was first claimed by Elie Metchnickoff at the begining of this century
The latter effect seems to be related to macrophage activity and recent studies have demonstrated that Lactobacillus and other lactic acid bacteria can increase the phagocytic capacity and enzymatic activity of mouse peritoneal cells (1923)
In order to determine the effect of L. acidophilus on the capacity of mice to clear a systemic infection, conventional Swiss mice were inoculated daily intragastrically with 0.1 ml of a suspension containing 109 colonyforming units (CFU)/ ml of L. acidophilus UFV-H2b20 for 7 days and their capacity to clear E. coli B41 from the blood stream was determined
Summary
The adverse effect of toxic metabolites from the intestinal microbiota was first claimed by Elie Metchnickoff at the begining of this century. Lactic acid bacteria, mainly those of the genus Lactobacillus, have been present in food and drugs for human and animal consumption These formulations containing live microorganisms or microbial stimulants that have some beneficial influence on the maintenance of a balanced intestinal microbiota and on the improvement of the host immune system are called probiotics [2]. Many other biological effects have been attributed to lactic acid bacteria, such as bile salt deconjugation [10], induction of higher tolerance to lactose when given to lactoseintolerant subjects [11,12], anticholesterolemic effects [13,14,15] and anticarcinogenic properties [16,17,18] The latter effect seems to be related to macrophage activity and recent studies have demonstrated that Lactobacillus and other lactic acid bacteria can increase the phagocytic capacity and enzymatic activity of mouse peritoneal cells (1923). Sato [24] has demonstrated that intravenous injection and ingestion of L. casei increase the survival of mice to infection with Listeria monocytogenes
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