INTRACELLULAR STAPHYLOCOCCUS-AUREUS ESCAPES THE ENDOSOME AND INDUCES APOPTOSIS IN EPITHELIAL-CELLS

We examined the invasion of an established bovine mammary epithelial c ell line (MAC-T) by a Staphylococcus aureus mastitis isolate to study the potential role of intracellular survival in the persistence of sta phylococcal infections, S, aureus cells displayed dose-dependent invas ion of MAC-T cells and intracellular survival, An electron microscopic examination of infected cells indicated that the bacteria induced int ernalization via a mechanism involving membrane pseudopod formation an d then escaped into the cytoplasm following lysis of the endosomal mem brane, Two hours after the internalization of S, aureus, MAC-T cells e xhibited detachment from the matrix, rounding, a mottled cell membrane , and vacuolization of the cytoplasm, all of which are indicative of c ells undergoing programmed cell death (apoptosis), BS 18 h, the majori ty of the MAC-T cell population exhibited an apoptotic morphology, Oth er evidence for apoptosis,vas the generation of MAC-T cell DNA fragmen ts differing in size by increments of approximately 180 bp and termina l deoxynucleotidyl transferase-mediated dUTP nick end labeling of the fragmented nuclear DNA of the infected host cells, These results demon strate that after internalization S, aurcus escapes the endosome and i nduces apoptosis in nonprofessional phagocytes.