Antagonism against Vibrio cholerae by bacterial diffusible compound in thefecal microbiota of rodents

In an ex vivo agar plate assay, we monitored the appearance of an inhibitor y halo against Vibrio cholerae from the feces of Wistar and Fischer rats ag ed 10 to 42 days. The frequency of Wistar rats showing halo increased from 0% (10 days) to a maximum of 80.0% (29 days) and then decreased to 53.3% (4 2 days). A similar pattern was obtained with Fischer rats but with a lower intensity (maximum frequency of 50.0% by day 36). In a separate experiment, when Wistar rats were fed a low-protein diet for 7 days, the inhibitory ha lo decreased drastically. Three apparently different colony morphologies we re isolated from the dominant fecal microbiota: a facultative anaerobe (FAN ) and two strict anaerobes (SAN). The ex vivo inhibitory test showed a halo around the feces of germfree mice monoassociated with the FAN bacterium or one of the SAN bacterium but not of the germfree ones. After oral challeng e of all groups with V. cholerae, a permissive and a drastic barrier effect s were observed in mice with FAN and SAN associated bacteria, respectively. The FAN and one SAN bacteria used in the in vivo challenges were identifie d as Escherichia coli and Streptococcus intermedius, respectively. The pote nt antagonism developed by the rat intestinal microbiota against V. cholera e seems to be due, in part, to diffusible compounds and this phenomenon dep ends apparently on age, strain and nutrition of the animals. These prelimin ary results also suggest that this effect was due to more than one bacteria l component at any given moment.