Escherichia coli is a leading cause of bacterial
mastitis in dairy cattle. It is most often transient in nature, causing an
infection that lasts 2 to 3 days. However, E. coli has been shown to cause a
persistent infection in a minority of cases. Mechanisms that allow for a persistent E. coli
infection are not fully understood. The goal of this work was to determine differences between E. coli strains originally isolated from dairy cattle with transient and persistent
mastitis. Using
RNA sequencing, we show gene expression differences in nearly 200 genes when bacteria from the two clinical phenotypes are compared. We sequenced the genomes of the E. coli strains and report genes unique to the two phenotypes. Differences in the wca operon, which encodes
colanic acid, were identified by
DNA as well as
RNA sequencing and differentiated the two phenotypes. Previous work demonstrated that E. coli strains that cause
persistent infections were more motile than those that cause transient
infections. Deletion of genes in the wca operon from a
persistent-infection strain resulted in a reduction of motility as measured in swimming and swarming assays. Furthermore,
colanic acid has been shown to protect bacteria from
complement-mediated killing. We show that transient-
infection E. coli strains were more sensitive to
complement-mediated killing. The deletion of genes from the wca operon caused a
persistent-infection E. coli strain to become sensitive to
complement-mediated killing. This work identifies important differences between E. coli strains that cause persistent and transient mammary
infections in dairy cattle.