DIFFERENTIATION AND IDENTIFICATION OF HUMAN FECAL ANAEROBIC-BACTERIA PRODUCING BETA-GALACTOSIDASE (A NEW METHODOLOGY)

Bacterial glycosidase activities, specially beta-galactosidase (beta-g al), are reduced in faeces from patients with Crohn's disease (CD). In order to test the hypothesis that an alteration of the colonic flora might be responsible for decreased faecal beta-gal activity in CD pati ents, we developed a new methodology designed to differentiate and enu merate anaerobic bacteria producing beta-gal. We used an enriched Colu mbia agar medium modified by addition of -bromo-4-chloro-5-indolyl-bet a-D-galactopyranoside (X-gal) and tested it on different faecal bacter ial strains. The presence of blue diffuse zones with various sizes sur rounding bacterial colonies clearly differentiated Bifidobacterium, Ru minococcus, Bacteroides and one of five strains of Lactobacillus teste d from other beta-gal positive bacteria. When the X-gal medium was app lied to the analysis of normal human faecal flora, 57%+/-29 (mean+/-S. D.) of the colonies growing on this medium were surrounded by blue hal oes. Among them, all colonies, characterized by a large blue diffuse r ing, were identified as bifidobacteria.