Selection of lactic acid bacteria as probiotic strains by in vitro tests

Abstract

Lactobacillus strains isolated from the colonic mucosa of healthy individuals (355) and Lactic Acid Bacteria isolated from fermentation of ecologically cultured rye (180) were screened from binding of porcine mucin, expression of cell surface hydrophobicity and binding of collagen, fibronectin, fibrinogen, vitronectin and heparin. Seven strains (L. plantarum, L. paracasei ssp. paracasei, Leuconostoc mesenteroides and pediococcus pentosaceus) were then selected for further studies. These strains all tolerated exposure to 20 % bile for 1 hr and pH 2,5 for 2 hrs, i.e. they have properties enabling them to survive transport through the gastrointestinal (GI) tact to the colon. All strains could utilise inulin or amylopectin as a sole carbon source during in vitro culture. Three strains produced beta-galactosidase, which has been proposed to alleviate symptoms of lactose intolerance. They produced antimicrobial substance(s) with activity against the homologous strain and other gram-positive bacteria. Exposure of Lactoacillus strains to pH 5 for 1 hr induced de novo production of several proteins, five of which cross-reacted with strass proteins. This may protect other surface proteins and adhesins during transport through the GI-tract. Four LAB strains studied transcribed NF-kB to the nucleus of microphage U 937. This induced induction of pro-inflammatory cytokine (IL-8) and anti-inflammatory (IL-10) by L. paracasei ssp.paracasei F19, L. plantarum 2592 and Pediococcus pentosaceus 16:1(10 up to 7 cell, 24 hrs) produced antioxidants, equivalent to 100 ug vitamin C. Since the availability of antioxidants decreases rostrally in the GI-tract production of antioxidants by colonic bacteria provides a beneficial effect in scavenging free radicals. The selected seven strains have been shown to survive transport to the colonic mucosa, and to have properties which makes them attractive candidates for use as probiotics.