Apoptosis of murine peritoneal macrophages induced by an avian pathogenic strain of Escherichia coli

Abstract

The mechanisms used by avian strains of Escherichia coli to invade the respiratory epithelia, leading to septicemia in poultry, are not well-established. In this work, we show that resident murine peritoneal macrophages infected in vitro with an avian strain of E. coli underwent apoptosis 4 h after infection (55.6% of apoptosis in infected cells versus 3.5% in non-infected cells). Heat-inactivated bacteria did not induce apoptosis and the inhibition of phagocytosis by pretreatment of cells with cytochalasin D reduced the number of apoptotic cells from 55.6 to 13.9% ( P<0.05), showing that the bacteria must be intracellularly located and viable to induce apoptosis. Therefore, these data suggest that induction of macrophage apoptosis may be a pathogenic mechanism employed by avian E. coli to circumvent the host defences and invade the respiratory epithelia.