Effect of staphylococcal beta toxin on the cytotoxicity, proliferation and adherence of Staphylococcus aureus to bovine mammary epithelial cells

The effect of staphylococcal beta toxin on the cytotoxicity, proliferation and adherence of S. aureus to bovine mammary epithelial cells was studied. Bovine erythrocytes and mammary epithelial cells were incubated with purified staphylococcal cu and beta toxins and with culture supernatants from S. aureus M60 and two mutant strains that are negative for either the production of alpha (DU5789(alpha-)) or beta (DU5846(beta-)) toxin. Lysis of bovine erythrocytes was due primarily to beta toxin. Alpha toxin increased the lysis of bovine erythrocytes by purified beta toxin, but the presence of ct toxin in culture supernatants from S. aureus did not increase the lysis of bovine erythrocytes. Purified beta toxin was cytotoxic to mammary secretory epithelial cells, but to a lesser extent than a toxin. Together they exhibited an additive effect on mammary epithelial cells. inactivation of the alpha toxin-gene of S. aureus M60 decreased the cytotoxic effect on mammary epithelial cells to a greater extent than the inactivation of the beta toxin-gene. Also, the relative percentages of DU5789(alpha-) and DU5846(beta-) adhering to mammary cell monolayers, the number and size of colonies and the number of infected epithelial cells decreased. This in vitro study showed that beta toxin damages bovine mammary secretory epithelial cells, increases the damaging effects of a toxin, increases the adherence of S. aureus to mammary epithelial cells and increases the proliferation of S. aureus.