Several bacterial strains are currently used as probioties. Sixteen of them belonging to the genera: Bifidobacterium. Enterococcus. Lactobacillus and Streptococcus, were selected to test short-ehain fatty acids (StJFAs) production in w‘tm and/‘er in viva. The probiotic strains were monoeultivated in specific media and/or monoassoeiated with NMRl-Kl germfree (GF) mice. The individual and total amounts of SCFAs were measured in the media and in the large intestinal content of the ex-GF mice. All the samples were assayed by gas-liquid chromatography. We found that commercially available media contain detectable amounts of acetic and propionic acids. When cultivated in vitro. none of the probiotie strains was able to increase the amounts of SCFAS present in the medium. Rather, a tendency to lowering the concentration of SCFAs following cultivation. was observed. We also found that commercially available laboratory rodents chow contained detectable amount of all SCFAs. When the probiotics were monoinoculated t0 GF animals, nine out of sixteen groups of mice showed higher amount of intestinal SCFAS than in the GF control group. Acetic acid was the dominant one. In all eases. however, the values of the SCFAs were far from those found in conventional mice.The results clearly underline the importance of working with laboratory animals with a known flora. i. e. gnotobiotie animals, when the biochemical “profile" eta prohiotie is worked out
