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 MccPDIproducing 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 = 0Á003). MccPDI-producing E. coli composed a higher log percentage of the total population of lactose-fermenting bacteria in the faeces (5Á51 log CFU per 8Á03 log CFU) compared with the knockout strain (2Á6 log CFU per 8Á23 log CFU) (P = 0Á01), and it was more consistently recovered from the lower gastrointestinal tract at the time of necropsy (P = 0Á01). 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.
Vaccination with Salmonella enterica serovar Typhimurium lacking DNA adenine methyltransferase confers cross-protective immunity against multiple Salmonella serotypes. The mechanistic basis is thought to be associated with the de-repression of genes that are tightly regulated when transiting from one microenvironment to another. This de-repression provides a potential means for the production of a more highly expressed and stable antigenic repertoire capable of inducing cross-protective immune responses. To identify genes encoding proteins that may contribute to cross-protective immunity, we used a Salmonella Typhimurium DNA adenine methyltransferase mutant strain (UK-1 dam mutant) derived from the parental UK-1 strain, and assessed the transcriptional profile of the UK-1 dam mutant and UK-1 strain grown under conditions that simulate the intestinal or endosomal microenvironments encountered during the infective process. As expected, the transcriptional profile of the UK-1 dam mutant identified a set of genes more transcriptionally active when compared directly to UK-1, and stably transcribed in biologically relevant culture conditions. Further, 22% of these genes were more highly transcribed in comparison to two other clinically-relevant Salmonella serovars. The strategy employed here helps to identify potentially conserved proteins produced by the UK-1 dam mutant that stimulate and/or modulate the development of cross-protective immune responses toward multiple Salmonella serotypes.
A single 5-year-old, white homing pigeon (Columba livia domestica) was submitted from a flock of 30 birds. The bird was bright alert and responsive upon presentation. One other bird was sick and two had died. The reported duration of illness was six months. Birds were noted to have a full crop but losing weight.
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