Microcin MccPDI reduces the prevalence of susceptible Escherichia coli in neonatal calves.

Abstract

Microcin MccPDI-producing Escherichia coli have a fitness advantage in dairy calves. For this project, we determined whether MccPDI is responsible for the in vivo fitness advantage, which is a necessary condition before MccPDI strains can be considered viable candidates for inhibiting pathogenic serovars of E.coli. Neonatal calves were coinoculated with either MccPDI-producing E.coli or MccPDI-knockout mutants in conjunction with a susceptible strain. After 6days, the MccPDI-producing E.coli-25 strain clearly dominated the E.coli-186 susceptible strain in the inoculated calves (P=0·003). MccPDI-producing E.coli composed a higher log percentage of the total population of lactose-fermenting bacteria in the faeces (5·51logCFU per 8·03logCFU) compared with the knockout strain (2·6logCFU per 8·23logCFU) (P=0·01), and it was more consistently recovered from the lower gastrointestinal tract at the time of necropsy (P=0·01). Our findings support the hypothesis that MccPDI is functional in vivo and it is most likely responsible for a fitness advantage in vivo. MccPDI-producing E.coli strongly inhibit pathogenic E.coli strains in vitro. We show herein that MccPDI functions in vivo, and thus, these strains may be candidate probiotics against pathogenic strains of E.coli.