Shigella flexneri is trapped in polymorphonuclear leukocyte vacuoles and efficiently killed

We examined the bactericidal activity of polymorphonuclear leukocytes (PMN) against an invasive wild-type strain of Shigella flexneri (M90T) and a plasmid-cured noninvasive derivative (BS176). Both Shigella strains, as well as a rough strain of Escherichia coli, were killed with similar efficiencies by intact inflammatory PMN in room air and under N-2 (i,e,, killing was O-2, independent), Bacterial killing by PMN extracts was substantially inhibited by antibodies to the bactericidal/permeability-increasing protein (BPI), Whereas mild-type Shigella escapes from the phagosome to the cytoplasm in epithelial cells and macrophages, wild-type Shigella was trapped in the phagolysosome of PMN as visualized by electron microscopy. The efficient killing, of Shigella by PMN suggests that these inflammatory cells may not. only contribute initially to the severe tissue damage characteristic of shigellosis but also ultimately participate in clearance and resolution of infection.