Factors influencing adherence of Streptococcus dysgalactiae to bovine mammary epithelial cell monolayers

Factors that affected adherence of Streptococcus dysgalactiae to monolayers of primary bovine mammary epithelial cells and to a bovine mammary epithelial transformed cell line were evaluated. Cell culture medium inhibited more than 99% of binding of S. dysgalactiae to plastic and was as effective as several blocking agents in decreasing adventitious adherence of this organism to plastic. Adherence of two strains of S. dysgalactiae (UT516 and UT519) was higher to a transformed mammary epithelial cell line (2.85% and 0.83%, respectively) than to primary bovine mammary epithelial cells (0.45% and 0.52%, respectively). Measurement of the extent of bacterial adherence to cell monolayers showed that adherence was affected by inoculum size. This indicated that the process was mediated by saturable cell receptors and allowed selection of bacteria:epithelial cell ratios not approaching saturating conditions (< 1500:1). In addition, reduction of bacterial adherence by more than 90% following cell fixation indicated that cell surface proteins played a major role in this process. Delineation of bacterial and epithelial cell factors influencing adherence of S. dysgalactiae to mammary epithelial cell monolayers resulted in the development of an in vitro method for quantifying bacterial adherence to cell monolayers.