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

Abstract

The effect of staphylococcal β 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 α and β toxins and with culture supernatants from S. aureus M60 and two mutant strains that are negative for either the production of α (DU5789 α−) or β (DU5846 β−) toxin. Lysis of bovine erythrocytes was due primarily to β toxin. Alpha toxin increased the lysis of bovine erythrocytes by purified β toxin, but the presence of α toxin in culture supernatants from S. aureus did not increase the lysis of bovine erythrocytes. Purified β toxin was cytotoxic to mammary secretory epithelial cells, but to a lesser extent than α toxin. Together they exhibited an additive effect on mammary epithelial cells. Inactivation of the α toxin-gene of S. aureus M60 decreased the cytotoxic effect on mammary epithelial cells to a greater extent than the inactivation of the β toxin-gene. Also, the relative percentages of DU5789 α− and DU5846 β− 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 β toxin damages bovine mammary secretory epithelial cells, increases the damaging effects of α toxin, increases the adherence of S. aureus to mammary epithelial cells and increases the proliferation of S. aureus.