VIRULENCE FACTORS OF STREPTOCOCCUS-UBERIS ISOLATED FROM COWS WITH MASTITIS

For intramammary infections (IMI) to occur, mechanisms associated with avoidance of phagocytic defenses, rapid growth of bacteria, adherence of bacteria to epithelial cells, and/or bacterial colonization of mam mary tissue are probably present. During the last decade, several pote ntial virulence factors of Streptococcus uberis have been identified. Some of these factors are cell-associated while other factors are extr acellular. Proposed antiphagocytic factors of S. uberis include capsul e, neutrophil toxin, M-like protein and R-like protein. Activation of plasminogen by S. uberis has been proposed as an important mechanism f or this organism to obtain nutrients for optimal bacterial growth. Pot ential virulence factors produced by S, uberis and released extracellu larly include hyaluronic acid capsule, hyaluronidase and uberis factor . Streptococcus uberis isolated from bovine IMI adhere to and invade m ammary epithelial cells. Involvement of intact microfilaments and de n ovo eukaryotic protein synthesis are required for bacterial invasion o f mammary epithelial cells; a process that appeared to occur by a rece ptor-mediated endocytosis mechanism. De novo bacterial protein synthes is was also required for invasion of S, uberis into mammary epithelial cells. Furthermore, S. uberis survived within mammary epithelial cell s for extended periods of time without losing viability or damaging th e eukaryotic cell. Further research directed towards characterization of host-pathogen interactions that take place during the early stages of S, uberis intramammary infection are needed to enhance our understa nding of pathogenesis and thus contribute to development of methods to minimize production losses associated with S. uberis mastitis in dair y cows.