THE ROLE OF O-POLYSACCHARIDE IN THE PATHOGENICITY OF MAMMARY PATHOGENIC ESCHERICHIA COLI

Mastitis, infection of the udder, is an ongoing problem in dairy cows, with destructive consequences locally and worldwide, both financially and from health and welfare aspects. Multiple bacterial species have been accused of causing mastitis, Escherichia coli (E. coli) amongst them. Through an unknown mechanism some strains acquire the ability to induce disease in the mammary gland. Despite years of research, no efficient measures to prevent and treat mastitis are available, mainly because it is unknown how E. coli generate their pathologic effects. The goal of this research was to identify and explore new virulence factors of mammary pathogenic E. coli (MPEC). An important virulence factor is the bacterial lipopolysaccharide (LPS), which consists of the O-polysaccharide (O-PS), the core, and the lipid A. Bacteria with a full length O-PS are considered smooth, while those without are rough. Smooth and rough forms of LPS can vary in the immune response they elicit. Upon screening of 50 clinical MPEC isolates 94% were found to be smooth. In the context of mastitis, LPS has been examined only in toll-like receptor signaling, and activation of inflammation and immune response. We suggest that the O-PS structure affects fitness and colonization in the mammary gland. Using our lactating mice model we discovered reduced virulence of a rough MPEC variant, and constructed a mutant of the galU gene, which is involved in metabolism of uridine-diphosphate-glucose. We characterized this mutant with respect to growth behavior, LPS structure, serum resistance, and pathogenicity in the model. Our results indicate a substantial role of LPS in MPEC pathogenesis, and might shed light on new targets for development of preventive and therapeutic solutions for mastitis.