Inhibition ofShigella sonneiand EnterotoxigenicEscherichia coliby Volatile Fatty Acids in Mice

Abstract

The role of volatile fatty acids (VFA) in resistance against the colonisation of the intestinal tract ofmice with two enteric pathogens, Shigella sonnei 3SR and enterotoxigenic E. coli 2SR (ETEC 2SR) was determined. The implantation dose 50 (IDSO) of S. sonnei 3SR strain for untreated mice was greater than 5.0 x lo9 viable cells and was 1.8 x lo6 viable cells for ETEC 2SR. Administration of streptomycin to the mice prior to challenge lowered the ID50 to fewer than one viable cell for both organisms. The antibiotic caused an increase in the pH of caecal contents from 6.66 in untreated animals to 6.94 in treated animals and a decrease in total VFA concentrations from 109.1 1 microequivalent per ml in untreated animals to 78.3 1 microequivalent per ml in treated animals. The discontinuation of streptomycin treatment resulted in a gradual restoration of colonisation resistance accompanied by an increase in total VFA concentration and a decrease in pH of caecal contents. These values returned to pre-treatment levels by day 7. VFA were added to nutrient broth in concentrations present in the caeca of either untreated or streptomycin treated mice and the pH levels were adjusted accordingly. S. sonnei 3SR multiplied in broth adjusted to simulate conditions present in the caeca of treated mice but failed to multiply in broth adjusted to simulate conditions present in the caeca of untreated mice. ETEC 2SR, on the other hand, multiplied in both types of broth but its total populations after 24 h incubation were significantly smaller in broth adjusted to simulate conditions present in the caeca of untreated mice.The results demonstrate that the multiplication of both pathogens is inhibited by the presence of VFA. They indicate that VFA operating at the pH level present in the intestinal tract of conventional mice represent important factors responsible for resistance against colonisation with S. sonnei and ETEC.

Comparison of the Efficacy of Cultures of Cecal Anaerobes as Inocula to Reduce Salmonella typhimurium Colonization in Chicks with or Without Dietary Lactose

“…The chicks provided dietary lactose had the lowest levels of colonization and the highest oxidation-reduction potentials. The VFA have been reported to inhibit growth of Salmonella enteritidis in mice with an oxidation-reduction potential as high as -200 mV (Pongpech and Hentges, 1989); the highest average oxidation-reduction potential in these experiments was -201.50. The higher oxidation-reduction potentials in the chicks provided dietary lactose may have been due to gases produced during the fermentation of lactose by the cecal flora.…”

“…Low oxidation-reduction potentials have been reported to increase the antibacterial activity of VFA (Meynell, 1963;Pongpech and Hentges, 1989). However, the significant increase in the cecal oxidation-reduction potential produced by dietary lactose had no adverse effect on reducing S. typhimurium cecal colonization.…”

“…Poultry rearing practices that prevent chicks from becoming colonized by these cecal anaerobes make the chicks more susceptible to sahnonellae colonization (Pivnick et al, 1981). Cecal anaerobes may decrease sahnonellae colonization by rapidly colonizing the intestinal tract of the young chicks (Pivnick et al, 1981), by competing for attachment sites on the intestinal wall (Snoeyenbos et al, 1979), or by producing bacteriostatic or bactericidal short-chained volatile fatty acids (VFA) (Barnes et al, 1979(Barnes et al, , 1980Corrier et al, 1990a,b;Hinton et al, 1990) that inhibit the growth of enteropathogens (Meynell, 1963;Bohnhoff et al, 1964b;Barnes et al, 1979;Que et al, 1986;Pongpech and Hentges, 1989).…”

Role of Volatile Fatty Acids in Development of the Cecal Microflora in Broiler Chickens during Growth

“…Reports concerning correlations between volatile fatty acids and Enterobacteriaceae have mainly focused on the intestines of mice (4,8,9,17). Unfortunately, in these reports, some contradictory results have been shown.…”

Inhibitory Effects of Volatile Fatty Acids and Low pH on the Multiplication of Enteric PathogensIn Vitroin Caecal Contents of Mice

“…A previous study provided evidence that these factors influenced the susceptibility of mice to colonisation with S. sonnei 3SR and ETEC 2SR by showing that there was a positive correlation between VFA concentrations in the mouse's caecum and colonisation resistance against the two pathogens. 16 The concentrations of VFA and the pH level observed in the caecum were shown to be inhibitory against both S. sonnei 2SR and ETEC 2SR in nutrient broth.I6…”