Effects of lactoferrin and milk on adherence of Streptococcus uberis to bovine mammary epithelial cells.

Objective: To determine whether lactoferrin (LF) or milk influenced adherence of Streptococcus uberis to bovine mammary epithelial cells.
Sample Population: Three strains of S uberis from cows with mastitis, pooled milk samples from 3 clinically healthy Jersey cows early in the lactation period, and bovine mammary epithelial cells from a clonal cell line.
Procedures: Adherence of S uberis to bovine mammary epithelial cells in the presence of various concentrations of LF or milk and after pretreatment of bacteria with LF or milk was tested. Bacteria were cultured with mammary epithelial cell monolayers for 1 hour. The culture supernatant was removed, and the epithelial cells were lysed. Adherence index was calculated as number of colony-forming units (CFU) in the cell lysate divided by number of CFU in the supernatant times 10,000.
Results: All 3 strains of S uberis were found to bind to purified LF and LF in milk. Addition of LF to the culture medium enhanced adherence of all 3 strains to mammary epithelial cells, whereas addition of milk enhanced adherence of 2 strains and decreased adherence of the third. Pretreatment of bacteria with LF or milk increased adherence of 1 of the strains but decreased adherence of the other 2. Increased adherence was antagonized by rabbit antibovine LF antibody.
Conclusions: Results suggest that LF may function as a bridging molecule between S uberis and bovine mammary epithelial cells, facilitating adherence of the bacteria to the cells.