EFFECTS OF STAPHYLOCOCCUS-AUREUS PRODUCTS ON GROWTH AND FUNCTION OF BOVINE MAMMARY MYOEPITHELIAL CELLS IN-VITRO

The effects of culture supernatants conditioned by the growth of Staph ylococcus aureus M60 on in vitro growth and functional properties of b ovine mammary myoepithelial cells were examined. Myoepithelial cell pr oliferation was reduced by Staph. aureus M60 culture supernatants. Exp osure of myoepithelial cells to culture supernatants of isogeneic muta nts of Staph. aureus M60 that produced either alpha or beta toxins red uced proliferation, but to a lesser extent than supernatants from the mild, type strain. Thus, alpha and beta toxins may play some role in a ffecting myoepithelial cell proliferation. Of the cells tested, 42% co ntracted following addition of oxytocin (10(-7) M) in the culture medi um. Treatment of myoepithelial cells for 15 min with Staph. aureus M60 supernatants, prior to addition of oxytocin in tile culture medium, i ncreased the number of cells that contracted to 92%. Exposure of cells for 3 h to the same supernatant, prior to addition of oxytocin in the culture medium, abolished oxytocin responsiveness; had no effect on i mmunolocalization of actin and vimentin, but affected. tile localizati on of alpha-actinin within myoepithelial cells. Treatment of myoepithe lial cells for 3 h with a combination of purified staphylococcal prote inases XVI and XVII-B abolished oxytocin responsiveness and mimicked t he effect of the Staph. aureus culture supernatant. We conclude that S taph. aureus M60 culture supernatant affected proliferation and functi onal properties of myoepithelial cells.