DEVELOPMENT AND APPLICATION OF AN IN-VITRO METHODOLOGY TO DETERMINE THE TRANSIT TOLERANCE OF POTENTIALLY PROBIOTIC LACTOBACILLUS AND BIFIDOBACTERIUM SPECIES IN THE UPPER HUMAN GASTROINTESTINAL-TRACT

An in vitro methodology which mimics in vivo human upper gastrointesti nal transit was developed, The transit tolerance of potentially probio tic Lactobacillus and Bifidobacterium species was determined by exposi ng washed cell suspensions at 37 degrees C to a simulated gastric juic e (pH 2.0), containing pepsin (0.3% w/v) and sodium chloride (0.5% w/v ), and a simulated small intestinal juice (pH 8.0), containing pancrea tin USP (1 g l(-1)) and sodium chloride (5 g l(-1)), and monitoring ch anges in total viable count periodically. The methodology was also emp loyed to determine the effect of adding milk proteins (1 g l(-1)), hog gastric mucin (1 g l(-1)) and soyabean trypsin-chymotrypsin inhibitor [SBTCI] (1 g l(-1)) on transit tolerance. The majority (14 of 15) of isolates lost > 90% viability during simulated gastric transit. Only o ne isolate, Lactobacillus fermentum KLD, was considered intrinsically resistant. The addition of milk, proteins, singly and in combination, generally improved gastric transit tolerance. In this regard, two isol ates, Lact. casei 212.3 and Bifidobacterium infantis 25962, exhibited 100% gastric transit tolerance in the presence of milk proteins. In ge neral, the addition of hog gastric mucin did not influence simulated g astric transit tolerance of lactobacilli but tended to increase that o f bifidobacteria. However, it increased that of Lact. casei 242 and La ct. salivarius 43338 but diminished that of B. bifidum 2715 and B. ani malis Bo. Selected bile salts-resistant isolates were intrinsically to lerant to simulated small intestinal transit. Only Lact. casei F19 and B. adolescentis 15703T showed significant reduction in viability afte r 240 min. In general, the addition of milk proteins and SBTCI did not affect simulated small intestinal transit tolerance. However, they si gnificantly improved the intrinsic resistance of Lact. casei F19 but d iminished that of B. breve 15700T. It is concluded that, whereas the m ajority of bile salts-resistant lactobacilli and bifidobacteria may be intrinsically sensitive to gastric transit, they are intrinsically re sistant to small intestinal transit. In addition, it is postulated tha t milk proteins and mucin may function as both buffering agents and in hibitors of digestive protease activity in vivo, thereby protecting in gested bacterial strains during upper gastrointestinal transit.