Oxygen-independent killing of Bacteroides fragilis by granule extracts from human polymorphonuclear leukocytes

Granule proteins from human neutrophils were prepared with acetate, and their antibacterial activity against Bacteroides fragilis was determined. Activity was highly dependent on pH; greatest strength and low bacterial numbers. Killing was inhibited by incubation temperatures of less than 37°C. Eight times more extract was required to kill 50% of stationary-phase bacteria, completed with those growing in logarithmic phase. The antibacterial effect of granule extract was destroyed by boiling, but some activity was retained after heating to 56°C and 80°C. Granule extract activity was tested under conditions in which oxygen-dependent antibacterial systems were inhibited. The rate and extent of killing was not affected by anaerobiosis, sodium azide, or cysteine hydrochloride. These results suggest that the activity of granule extract is independent of oxidative antibacterial systems, and therefore, under conditions that occur in anaerobic infections, potent leukocyte granule-associated mechanisms exist for the destruction of B. fragilis.