Postgenomics Characterization of an Essential Genetic Determinant of Mammary Pathogenic .

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 (MPEC). By whole-genome sequencing analysis of 40 MPEC and 22 environmental ("dairy-farm" [DFEC]) strains, we found that only the locus () for ferric dicitrate uptake was present in the core genome of MPEC and that it was absent in DFEC genomes ( < 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 gene and of the inner membrane transport component gene was upregulated in bacteria recovered from experimental intramammary infection. The presence of the system was shown to affect the ability of to grow in milk. While the rate of growth in milk of -positive () DFEC was similar to that of MPEC, it was significantly lower in DFEC lacking Furthermore, deletion of reduced the rate of growth in milk of MPEC strain P4, whereas -transformed non-mammary gland-pathogenic DFEC strain K71 gained the phenotype of the level of growth in milk observed in MPEC. The role of in intramammary pathogenicity was investigated in cows, with results showing that an MPEC P4 mutant lacking lost its ability to induce mastitis, whereas the 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. Bovine mastitis is the major infectious disease in dairy cows and the leading cause of economic loss to the global dairy industry, directly contributing to the price of dairy products on supermarket shelves and the financial hardships suffered by dairy farmers. Mastitis is also the leading reason for the use of antibiotics in dairy farms. Good farm management practices in many countries have dramatically reduced the incidence of contagious mastitis; however, the problems associated with the incidence of environmental mastitis caused by bacteria such as have proven intractable. bacteria cause acute mastitis, which affects the health and welfare of cows and in extreme cases may be fatal. Here we show for the first time that the pathogenicity of causing mastitis in cows is highly dependent on the ferric citrate uptake system that allows the bacterium to capture iron from citrate. The Fec system is highly expressed during infection in the bovine udder and is ubiquitous in and necessary for the bacteria that cause mammary infections in cattle. These results have far-reaching implications, raising the possibility that mastitis may be controllable by targeting this system.