Genomic and Transcriptomic Analysis of Escherichia coli Strains Associated with Persistent and Transient Bovine Mastitis and the Role of Colanic Acid.

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, has been shown to cause a persistent infection in a minority of cases. Mechanisms that allow for a persistent infection are not fully understood. The goal of this work was to determine differences between 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 strains and report genes unique to the two phenotypes. Differences in the operon, which encodes colanic acid, were identified by DNA as well as RNA sequencing and differentiated the two phenotypes. Previous work demonstrated that strains that cause persistent infections were more motile than those that cause transient infections. Deletion of genes in the 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 strains were more sensitive to complement-mediated killing. The deletion of genes from the operon caused a persistent-infection strain to become sensitive to complement-mediated killing. This work identifies important differences between strains that cause persistent and transient mammary infections in dairy cattle.