Fermentation of radiolabelled substrates by batch cultures of caecal microflora maintained in a continuous-flow culture.

Glucose- and lactose-based media containing either 14C-labelled glucose, galactose, lactose or lactic acid were inoculated with anaerobic cultures of chicken caecal bacteria maintained for 121 d in a continuous-flow (CF) culture. The culture was previously shown to reduce Salmonella colonization in the caeca of chicks inoculated with the culture and the reduction was associated with increases in volatile fatty acids. The distributions of 14C were determined among the fermentation products, especially acetic, propionic and lactic acids. After 12 h of incubation and fermentation, variations were observed in the total amounts of 14C, from each 14C-labelled substrate, detected as acetic and propionic acids in the glucose- and lactose-based media, respectively: 92.9 and 89.4% of 14C-glucose, 77.0 and 44.0% of 14C-galactose, 0.0 and 76.9% of 14C-lactose, and 76.5 and 93.2% of lactic acid in the two media, respectively. The results from this study indicate that carbohydrate metabolism by the CF culture was a major source of acetic and propionic acids and that lactic acid was an important metabolic intermediate for the synthesis of the volatile fatty acids.