Proteomic analysis reveals protein expression differences in Escherichia coli strains associated with persistent versus transient mastitis

UNLABELLED: Escherichia coli is a leading cause of bacterial mastitis in dairy cattle. Typically this infection is transient in nature, causing an infection that lasts 2-3days. However, in a minority of cases, E. coli has been shown to cause a persistent infection. The mechanisms that allow for a persistent E. coli infection are not fully understood. The goal of this work was to determine protein expression differences between E. coli strains isolated from dairy cattle with transient and persistent mastitis infections. Three persistent and three transient mastitis-derived strains of E. coli were compared using iTRAQ in a shotgun proteomics experiment. Expression data for 1127 proteins were determined. Of these, 28 proteins were associated with expression changes correlated with a difference in disease phenotype. Of particular interest were proteins that have been shown to be essential for bacterial swimming and swarming. Bacterial swimming and swarming assays showed that the strains from the persistent mastitis cases were significantly better in these motility assays than the strains from the transient cases. This work identifies important protein expression differences between E. coli strains that cause a persistent versus a transient infection as well as demonstrates a corresponding difference in the associated bacterial motility phenotypes.

BIOLOGICAL SIGNIFICANCE: The significance of this study is that proteins associated with bacterial swimming and swarming are more highly expressed in the E. coli strains that cause persistent mastitis infections. These findings point to swimming and swarming as important mechanisms involved in how a pathogen establishes a persistent infection in the mammary gland. The role of swimming and swarming in clinical mastitis clearly requires further experimentation.