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

摘要

Aims: 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. Methods and Results: Neonatal calves were coinoculated with either MccPDI-producing E. coli or MccPDI-knockout mutants in conjunction with a susceptible strain. After 6 days, 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 (5.51 log CFU per 8.03 log CFU) compared with the knockout strain (2.6 log CFU per 8.23 log CFU) ( P=0.01), and it was more consistently recovered from the lower gastrointestinal tract at the time of necropsy ( P=0.01). Conclusion: Our findings support the hypothesis that MccPDI is functional in vivo and it is most likely responsible for a fitness advantage in vivo. Significance and Impact of the Study: 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.