Detection and characterization of Bifidobacterium crudilactis and B. mongoliense able to grow during the manufacturing process of French raw milk cheeses

BACKGROUND: The study of a production chain of raw milk cheeses (St Marcellin, Vercors area, France) led to the isolation of two Bifidobacterium populations: B. crudilactis and B. mongoliense, that were able to grow along the production chain. The aims of this study were to further detect and characterize these bacteria along the process and evaluate the ability of some strains to survive or grow in adverse conditions. RESULTS: Using PCR coupled with restriction fragment length polymorphism, B. crudilactis and B. mongoliense were detected in respectively 77% and 30% of St Marcellin cheeses from production chain after 21 days of ripening. They were present in more than half of all analyzed retail cheeses with counts going from 1.6 to 5 log cfu g-1 for B. crudilactis and 1.4 to 7 log cfu g-1 for B. mongoliense. Bifidobacterium mongoliense was sensitive to pH 2, with an observed decrease of at least 3 log for both studied strains (FR49/f/2 and FR41/2) after 1 h incubation. At pH 3, no significant decrease was observed. Good survival was observed for the same strains in presence of pancreatic juice with a decrease of less than one log. Survival of strain FR49/f/2 was better than FR41/2 with a decrease of 3 logarithms (in presence of 1% bile salts) and almost 2 logarithms (in presence of 0.5% bile salts). The genotypic analyses using total DNA-DNA hybridization, GC% content, 16S rRNA gene sequencing and multilocus sequencing analysis (MLSA) confirmed the classification of Bifidobacterium. crudilactis and B. mongoliense into two different clusters well separated from other bifidobacteria clusters. CONCLUSIONS: According to the observed characteristics such as survival in adverse conditions and their ability to grow under 12°C during the manufacturing process of the cheeses, which has never been described for bifidobacteria and which is a very interesting technological asset, these B. crudilactis and B. mongoliense strains should be further investigated for a potential use in new food or in food supplements.