Competition mechanisms of lactic acid bacteria and bifidobacteria: Fermentative metabolism and colonization

Enzyme activities (α- and β-glucosidases, α- and β-galactosidases and β-fructofuranosidase) and organic acid production of four strains of lactic acid bacteria (LAB; Streptococcus thermophilus STY-31, Lactobacillus delbrueckii subsp. bulgaricus LBY-27, Lactobacillus casei LC-01 and Lactobacillus acidophilus LA-5) and Bifidobacterium lactis BB-12 were tested on milk and MRS fermentation broth with glucose, lactose or fructooligosaccharides (FOS) as carbon source. The highest β-galactosidase activity was found in L. acidophilus growing on milk. As compared to milk, α-glucosidase activity was increased with FOS by B. lactis, L. acidophilus and L. casei. The analysis of organic acids and short-chain fatty acids in the medium growth showed that lactate and acetate were the major fermentation metabolites produced by LAB and bifidobacteria, respectively. However, a metabolic shift towards more acetate and formate production, at the expense of lactate production, was observed during growth of L. casei on FOS. When grown on FOS as sole carbon source, L. acidophilus showed the highest production of lactate among the species tested. In addition, L. acidophilus demonstrated resistance to colonization against the intestinal pathogens Escherichia coli and Salmonella enterica in competition assays.