An. in vitro fermentation system capable of maintaining at least part of the microbial population of the contents of the porcine ileum has been developed. The system was tested over the pH range 6.0-8.5, anaerobically and at dissolved oxygen concentrations within the ranges detected in the ileum of piglets at weaning (50 and 100 mumol l-1). The results demonstrated that changes in pH and dissolved oxygen within these ranges had relatively little effect on the total numbers of aerobic and anaerobic bacteria. Lactic acid bacteria, enumerated anaerobically, showed changes in viable counts in response to pH changes but were apparently unaffected by changes in dissolved oxygen, although the proportion of aerotolerant species within this group was increased at high concentrations of dissolved oxygen. The relative proportions of lactobacilli and coliforms were similar to those reported in vivo when dissolved oxygen was present at a concentration of 50 mumol l-1. Under these conditions the simulated population was consistently found to resist colonization by an enterotoxigenic Escherichia coli, of a serotype known to cause weaning scours in the piglet.
Mixtures of strains of Lactobacillus spp., two of strains inhibitory to growth of the porcine enteropathogen Escherichia coli O149: K88ac: K91 in a co-culture screen, and one of strains with no effect on this pathogen, were examined to determine their effects on the retention of this pathogen in an in-vitro continuous culture system designed to maintain a representation of the porcine ileal microflora. Strains effective in co-culture also increased the rate of decline of the pathogen in the continuous culture. The inhibitory effect exceeded the displacement effect observed with non-inhibitory strains.
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