Postgenomics Characterization of an Essential Genetic Determinant of Mammary Pathogenic
Escherichia coli
Authors: Blum Shlomo E. , Goldstone Robert J. , Connolly James P. R. , Répérant-Ferter Maryline , Germon Pierre , Inglis Neil F. , Krifucks Oleg , Mathur Shubham , Manson Erin , Mclean Kevin , Rainard Pascal , Roe Andrew J. , Leitner Gabriel , Smith David G. E. 
Published: April 2018

Escherichia 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.

IMPORTANCE
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
Escherichia coli
have proven intractable.
E. coli
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
E. coli
causing mastitis in cows is highly dependent on the
fecIRABCDE
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
E. coli
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.