IN-VITRO LACTOSE FERMENTATION BY HUMAN COLONIC BACTERIA IS MODIFIED BY LACTOBACILLUS-ACIDOPHILUS SUPPLEMENTATION

Adaptation of the colonic flora to lactose may contribute to lactose d igestion in lactose maldigesters, and supplementation with Lactobacill us acidophilus may modify colonic fermentation of lactose and short-ch ain fatty acid production, We evaluated the capability of colonic bact eria to ferment lactose and the ability of L. acidophilus to modify la ctose fermentation by the colonic microflora in vitro, An anaerobic co ntinuous culture was established and inoculated with fresh samples of human feces, Lactose infusion was maintained at 25 g/d and pH at 6.7, L. acidophilus strain LA-1 (1.5 x 10(10) cells) was introduced into th e fermenter on d 0 or added daily on d 0 through 4, The control was th e continuous culture without the addition of lactobacilli. Rapid adapt ation of colonic bacteria to lactose occurred within 1-2 d, with a sig nificant decrease in lactose concentration and increase in P-galactosi dase activity, and lactose concentrations fell below 3 mmol/L by d 7, Supplementation with strain LA-I resulted in a significantly greater d ecrease in lactose concentration and greater increase in acetate and p ropionate production within the first day compared with the control gr oup, However, there was no significant difference between the fermenta tion treated with L. acidophilus daily and the control after the first day, These data suggest that the colonic bacteria adapt quickly to la ctose, causing efficient utilization of lactose. L. acidophilus supple mentation may enhance lactose fermentation during early periods when t he adaptation is not established in this model.