Escherichia coli M12 Genome sequencing. Escherichia coli M12

Mastitis caused by E. coli inflicts substantial burdens on the health and productivity of dairy animals. Strains causing mastitis may carry or express specific genes that distinguish them from other E. coli pathogenic types and promote infection of mammary glands, but so far these have not been identified. Therefore, it has been unclear whether disease severity is determined by relative virulence properties of the infecting strain, adaptation to growth in mammary glands, or solely by the immune status of the host animal. We show that a simple insect model can discriminate virulence potential of mastitis-associated E. coli. We identified a strain (M12) that readily kills Galleria mellonella larvae and grows prolifically in mouse mammary glands. We used genome-wide transposon mutagenesis and massively parallel sequencing to identify genes that contribute to M12 growth in G. mellonella, milk, and mouse mastitis infections. This extensive data set is the first screen for mastitis-associated E. coli fitness factors and provides the following contributions to the field: 1) Global comparison of genes required for different aspects of mastitis infection, 2) Discovery of a unique capsule that contributes to M12 virulence, 3) Conclusive evidence for the crucial role of iron scavenging systems in mastitis, particularly the ferric dicitrate transport system. Similar approaches applied to other mastitis-associated strains will uncover conserved targets for prevention or treatment, and provide a better understanding of their relationship to other extraintestinal E. coli pathogens.