Differential gene expression of three mastitis-causing Escherichia coli strains grown under planktonic, swimming, and swarming culture conditions

Authors: Lippolis, John; Brunelle, Brian; Reinhardt, Timothy; Sacco, Randy; Thacker, Tyler; Looft, Torey; Casey, Thomas

Submitted to: mSystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2016
Publication Date: 8/11/2016
Publication URL: http://handle.nal.usda.gov/10113/5498088
Citation: Lippolis, J.D., Brunelle, B.W., Reinhardt, T.A., Sacco, R.E., Thacker, T.C., Looft, T.P., Casey, T. 2016. Differential gene expression of three mastitis-causing Escherichia coli strains grown under planktonic, swimming, and swarming culture conditions. mSystems. 1(4):e00064-16.

Interpretive Summary: Infection of the udder (mastitis) is a major economic problem for the dairy industry. In the dairy industry, this disease alone accounts for 2 billion dollars a year in losses to the industry. Bacteria, such as Escherichia coli (E. coli), are the major cause of mastitis in dairy cows. In a previous publication we determined that there was a correlation between E. coli that could cause a persistent infection and bacterial motility. Bacteria can exhibit various type of motility. It is known that different types of motilities are associated with virulence. In this work we compare gene expression in bacteria that are grown in conditions that force three types or bacterial motility. Better understanding of the mechanisms of how bacteria can cause a persistent versus a transient infection is an important first step to better diagnostics and therapeutics.

Technical Abstract: Escherichia coli is a leading cause of intramammary infections in dairy cattle and is typically transient in nature. However, in a minority of cases, E. coli can cause persistent infections. Although the mechanisms that allow for a persistent intramammary E. coli infection are not fully understood, we have previously shown that proficient bacterial motility (swimming and swarming) in vitro is correlated with the persistent infection phenotype observed in cattle. In this work, three E. coli strains that cause persistent infections were grown in liquid culture media (planktonic), as well as on semi-solid media that promote swimming and swarming motility phenotypes. Using whole transcriptome RNA sequencing, we identified genes that were differentially expressed among these three growth conditions. We contend that better understanding of the genes that are differentially expressed due to the type of motility will yield important information about how bacteria can establish a persistent infection. Our data indicate that iron plays a critical role in motility, as genes associated with iron account for nearly 7% of all the genes that are differentially regulated. The addition of iron to the motility-promoting media has a negative effect on swarming and no effect on swimming, while the chelation of iron causes changes in the swimming pattern but little effect on swarming. Critically, bacterial motility is thought to play an important role in virulence. Elucidating the mechanisms that regulate bacterial motility and its relationship to persistent intramammary infections may provide new approaches in the development of intervention strategies, as well as facilitate the discovery of novel diagnostics and therapeutics. Unique to this report is the complete transcriptomics comparison of gene expression differences between growth in liquid LB, swimming plates, and swarming plates of three strains of E. coli.