The fate of ingested lactobacilli in the proximal small intestine.

A freeze-dried commercial preparation of Lactobacillus acidophilus and Lactobacillus bulgaricus (Lactinex) dissolved in skim milk was ingested by four nonfasting and seven fasting informed community volunteers in the Isolation Ward of the Center for Vaccine Development. Samples of jejunal fluid withdrawn from the volunteers at varying intervals were cultured for lactobacilli on a selective medium. Quantitative counts varied considerably amongst the individuals studied and also in the same person examined on two consecutive occasions. In general, however, it was shown that lactobacilli entered the small intestine and persisted in elevated numbers for about 3 h in fasting subjects and for up to 6 h in nonfasting individuals. By 4 h, counts in fasting volunteers had returned to base-line levels. Although both Lactobacillus species in Lactinex entered the intestine in approximately equal numbers, L. acidophilus was recovered from more samples and in slightly greater number than L. bulgaricus.