Effect of Lactobacilli on the Ecology of the Gastro-intestinal Microbiota Cultured in the SHIME Reactor

Evidence is presented that an established bacterial gastro-intestinal community can undergo significant changes upon addition of lactobacilli. Indeed, administration of doses of about log 10 8-9 CFU/day were shown to alter the gastro-intestinal community both in terms of population levels and biochemical activities. Four bacterial strains, namely two Lactobacillus plantarum species, Escherichia coli and Aeromonas hydrophila , were added separately to the SHIME reactor, an in vitro simulation of the human intestinal microbial ecosystem. The survival of these strains and their effect on the performance of the microbial ecosystem were studied. The experiments carried out with the L. plantarum strains revealed significant decreases of CH 4 -production, ?-glucuronidase activity and presence of total anaerobes, methanogens, gram-negative aerobes and anaerobes and enterobacteriaceae. However, within two weeks after the Lactobacillus supplementation was stopped, the ecological balance re-established towards the original microbiota. The results suggest that if these types of Lactobacillus strains were to be used as a probiotic, they should be supplemented daily at doses of 10 8 per capita to obtain a prolonged influence on the intestinal microbiota. Neither of the other strains had a significant effect on methane production or bacterial numbers of methanogens. During the administration of Escherichia coli , the ?-glucuronidase activity increased. Keywords: in vitro simulation, lactobacilli, intestinal microbiota, inoculation efficiency.