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

The mechanisms used by avian strains of Escherichia coli to invade the resp iratory epithelia, leading to septicemia in poultry, are not well-establish ed. In this work, we show that resident murine peritoneal macrophages infec ted 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 inhibit ion of phagocytosis by pretreatment of cells with cytochalasin D reduced th e 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. T herefore, these data suggest that induction of macrophage apoptosis may be a pathogenic mechanism employed by avian E. coli to circumvent the host def ences and invade the respiratory epithelia. (C) 1999 Published by Elsevier Science B.V. All rights reserved.