Survey studies have shown that E. coli diversity and population dynamics varies as a function of host diet, as well as gut morphology and dynamics. In a previous experimental study using laboratory rats, E. coli diversity and dynamics were shown to vary as a function of the proportion of insoluble fibre in the rat diet. However, there has been no study examining the effects on E. coli dynamics and diversity in animals fed diets rich in soluble as opposed to non-fermentable fibre.
Forty-five, 21-day old female (Wistar) rats were fed one of three different diets: 5% fibre, 26% fibre (insoluble cellulose) and a diet consisting of 50% of a basal diet and 50% cooked red kidney beans (rich in soluble fibre).
E. coli cell densities in animals fed a diet high non-fermentable fibre diet did not vary over the course of the experiment. In animals fed either a low fibre diet or one rich in soluble fibre, cell densities were initially higher than those observed in animals on high fibre diet, but after 3 - 4 weeks cell densities in these animals started to decline until cell densities were similar in all animals regardless of diet. Over 90% of >1500 isolates were represented by 3 ERIC genotypes: two B1 genotypes and a B2 genotype. The frequency of the B2 genotype declined in all animals once on the experimental diets, but the frequency of the B2 genotype continued to decline in the animals fed high soluble fibre diet.
This experiment demonstrates that the competitive advantage of particular E. coli strains in the GI tract varies with diet. The change observed in cell density came shortly after the animals attained sexual maturity suggests that perhaps the hormonal changes accompanying sexual maturity may influence E. coli.