Escherichia coli is an incredibly diverse group of bacteria that consist of both commensal and pathogenic strains that cause disease in a wide variety of tissues in many different animals. The current dogma, based on years of extensive molecular and genetic studies, is that individual strains have adapted to specific environments through acquisition of specific genes or come from lineages that are particularly suited to a unique tissue or host. However, mastitis-associated E. coli (MAEC) have thus far resisted such descriptions. The fitness and virulence factors of MAEC are poorly understood and molecular tools are rarely applied. This dissertation reports new approaches to assess virulence of MAEC strains, enabling comparative genomic studies across multiple strains as well as genome-wide analysis of specific successful MAEC isolates. I outline the identification of the first virulence factor of MAEC, a ferric dicitrate receptor that is essential for colonization of a lactating mammary gland in a murine model. Genes previously studied in the contexts of other extraintestinal E. coli infections were also implicated in mastitis. These include a type III capsule found in the MAEC strain M12, which is crucial for dissemination from the mammary gland to the spleen. A mutant unable to produce capsule had diminished lethality in Galleria mellonella and decreased kidney colonization in a mouse urinary tract infection. I also report a link between zinc uptake, bile salts, and capsule production. I have utilized a transposon mutant library paired with deep sequencing of transposon junctions to elucidate the fitness factors needed to grow in milk and colonization of both murine and insect models. This analysis implicates a broad set of genes and metabolic pathways pertinent to these conditions. In addition to Tn-seq, I sequenced 94 MAEC genomes and identified genes associated with disease severity, growth in milk, and colonization of mammary glands in cow and mouse models. Employing bioinformatic tools to interrogate the pan-genome, I identified genes that are involved in biofilm formation and adhesion that were specifically associated with either mild or severe disease. In summary, I have employed several powerful genetic, genomic, computational, and molecular approaches to the characterization of mastitis associated E. coli. This work provides the groundwork for future experiments to better understand the host-pathogen interface and a model for mastitis-associated E. coli.



College and Department

Life Sciences; Microbiology and Molecular Biology



Date Submitted


Document Type





mastitis, Tn-seq, GWAS, capsule, iron uptake, Escherichia coli, zinc, capsule



Included in

Life Sciences Commons