Abstract
ABSTRACTEscherichia coli are major bacterial pathogens causing bovine mastitis, a disease of great economic impact on dairy production worldwide. This work aimed to study the virulence determinants of mammary pathogenic E. coli (MPEC). By whole-genome sequencing analysis of 40 MPEC and 22 environmental (“dairy-farm” E. coli [DFEC]) strains, we found that only the fec locus (fecIRABCDE) for ferric dicitrate uptake was present in the core genome of MPEC and that it was absent in DFEC genomes (P < 0.05). Expression of the FecA receptor in the outer membrane was shown to be citrate dependent by mass spectrometry. FecA was overexpressed when bacteria were grown in milk. Transcription of the fecA gene and of the inner membrane transport component fecB gene was upregulated in bacteria recovered from experimental intramammary infection. The presence of the fec system was shown to affect the ability of E. coli to grow in milk. While the rate of growth in milk of fec-positive (fec+) DFEC was similar to that of MPEC, it was significantly lower in DFEC lacking fec. Furthermore, deletion of fec reduced the rate of growth in milk of MPEC strain P4, whereas fec-transformed non-mammary gland-pathogenic DFEC strain K71 gained the phenotype of the level of growth in milk observed in MPEC. The role of fec in E. coli intramammary pathogenicity was investigated in vivo in cows, with results showing that an MPEC P4 mutant lacking fec lost its ability to induce mastitis, whereas the fec+ DFEC K71 mutant was able to trigger intramammary inflammation. For the first time, a single molecular locus was shown to be crucial in MPEC pathogenicity.
Highlights
Escherichia coli are major bacterial pathogens causing bovine mastitis, a disease of great economic impact on dairy production worldwide
Despite the use of antibiotics, mastitis carries a substantial risk of mortality or severe morbidity resulting in culling of the affected animal [4], a factor which adds to the cost of this disease with respect to the economic and psychological well-being of dairy farmers, who often form strong emotional attachments with their livestock [5]
This method employed defining of genes that were present in the core genome of mammary pathogenic E. coli (MPEC) and yet absent in the core genome of closely related strains from the more widely available E. coli genomic resource
Summary
Escherichia coli are major bacterial pathogens causing bovine mastitis, a disease of great economic impact on dairy production worldwide. Bacteria in the species Escherichia coli are a principal causative agent of bovine mastitis (mammary pathogenic E. coli [MPEC]), costing dairy farmers in the European Union an estimated €2 billion per year, with a similar economic burden for the United States, where each case of mastitis has been estimated to cost $444 [1]. Given the high concentrations of citrate in bovine milk, it is pertinent that some E. coli strains possess a specific system to capture iron from ferric citrate (Fe-cit) This system, encoded by the fecIRABCDE locus, binds and translocates Fe-cit at the outer membrane via FecA and internalizes Fe via FecB, FecC, FecD, and FecE. We experimentally explored the contribution of the Fec system to E. coli mastitis
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