Effects ofStaphylococcus aureusproducts on growth and function of bovine mammary myoepithelial cellsin vitro

SUMMARYThe effects of culture supernatants conditioned by the growth ofStaphylococcus aureusM60 onin vitrogrowth and functional properties of bovine mammary myoepithelial cells were examined. Myoepithelial cell proliferation was reduced byStaph, aurexisM60 culture supernatants. Exposure of myoepithelial cells to culture supernatants of isogeneic mutants ofStaph, aureusM60 that produced either α or β toxins reduced proliferation, but to a lesser extent than supernatants from the wild type strain. Thus, α and β toxins may play some role in affecting myoepithelial cell proliferation. Of the cells tested, 42% contracted following addition of oxytocin (10–7M) in the culture medium. Treatment of myoepithelial cells for 15 min withStaph, aureusM60 supernatants, prior to addition of oxytocin in the culture medium, increased 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 immunolocalization of actin and vimentin, but affected the localization of α-actinin within myoepithelial cells. Treatment of myoepithelial cells for 3 h with a combination of purified staphylococcal proteinases XVI and XVII-B abolished oxytocin responsiveness and mimicked the effect of theStaph, aureusculture supernatant. We conclude thatStaph, aureusM60 culture supernatant affected proliferation and functional properties of myoepithelial cells.