Probiotic Treatment in vivo in Experimental Animals and in Man
There is some evidence suggesting that probiotics prevent infections caused by enteropathogens. About 47 different Lactobacillus strains have been tested in vitro for their ability to inhibit growth of a number of pathogens. Among the tested strains, L. rhamnosus 19070-2, L. reuteri DSM 12246, and L. rhamnosus LGG were identified most frequently in fecal samples; they were found in 10, eight, and seven of the 12 samples tested during the intervention period, respectively, whereas reisolations were less frequent in the washout period. Survival and reisolation of the bacteria in vivo appeared to be linked to pH tolerance, adhesion, and antimicrobial properties in vitro (94). The majority of the strains inhibited Yersinia entero colitica and Bacillus cereus and a few exhibited anti-microbial activities toward Staphylococcus aureus and Salmonella enterica serovar typhimurium (8).
Lactic acid bacteria in general may inhibit the growth of enteropathogens such as E. coli, H. pylori, Listeria monocytogenes, Salmonella spp. and others. This antagonistic activity is mediated either directly by the production of inhibitory substances such as lactic acid, hydrogen peroxide, bacteriocins, a-hydroxypropionaldehyde and other unidentified compounds or by competing with the pathogen for binding sites on the epitheliaL cell surface.
Another criterion for effective probiotic organisms is the adhesion to epithelial cells, a characteristic of several lactobacilli and some bifidobacteria. The factors mediating cell adhesion are still unknown. It has been suggested that proteinaceous factors are involved. Lipoteichoic acid participates in the adhesion of L. johnsonii La1 to epithelial Caco-2 cells (95).
A human feeding study conducted in 80 healthy volunteers showed that yogurt may be used as a vehicle for delivery of strain UCC118 to the human gastrointestinal tract with considerable efficacy in influencing gut flora and colonization. The investigators in Cork, Ireland, developed criteria for in vitro selection of probiotic bacteria that may reflect certain in vivo effects on the host, such as modulation of gastrointestinal tract microflora (18).