Host gastro-intestinal dynamics and the frequency of colicin production by Escherichia coli

The production of antimicrobial compounds known as colicins has been shown to be an important mediator of competitive interactions among Escherichia coli genotypes. There is some understanding of the forces responsible for determining the frequency of colicin production in E coli populations; however, this understanding cannot explain all of the observed variation. A survey of colicin production in E coli isolated from native Australian mammals revealed that the frequency of colicin production in strains isolated from carnivores was significantly lower than the frequency of production in strains recovered from herbivores or omnivores. The intestine of Australian carnivores is tube-like and gut turnover rates are rapid compared with the turnover rates of the intestinal tracts of herbivores and omnivores, all of which possess a hindgut fermentation chamber. A mathematical model was developed in order to determine if variation in gut turnover rates could determine if a host was more likely to harbour a colicin- producing strain or a non-producer. The model predicted that a colicin producer was more likely to dominate in the gut of a host with lower gut turnover rates, and a non-producer to dominate in hosts with rapid gut turnover rates.