THE POTENT ANTI-STAPHYLOCOCCUS AUREUS ACTIVITY OF A STERILE RABBIT INFLAMMATORY FLUID IS DUE TO A 14-KD PHOSPHOLIPASE-A2

The cell-free fluid (ascitic fluid, AF) of a sterile inflammatory peri toneal exudate elicited in rabbits is potently bactericidal for comple ment-resistant gram-negative as well as gram-positive bacterial specie s, This activity is absent in plasma, We now show that essentially all activity in AF against Staphylococcus aureus is attributable to a gro up IT 14-kD phospholipase A2 (PLA2), previously purified from AF in th is laboratory, Antistaphylococcal activity of purified PLA2 and of who le AF containing a corresponding amount of PLA2 was comparable and blo cked by anti-AF-PLA2 serum. At concentrations present in AF (similar t o 10 nM), AF PLA2 kills > 2 logs of 10(6) S. aureus/ml, including meth icillin-resistant clinical isolates, and other species of gram-positiv e bacteria, Human group II PLA2 displays similar bactericidal activity toward S. aureus (LD(90) similar to 1-5 nM), whereas 14-kD PLA2 from pig pancreas and snake venom are inactive even at micromolar doses, Ba cterial killing by PLA2 requires Ca2+ and catalytic activity and is ac companied by bacterial phospholipolysis and disruption of the bacteria l cell membrane and cell wall, These findings reveal that group II ext racellular PLA2, the function of which at inflammatory sites has been unclear, is an extraordinarily potent endogenous antibiotic against S, aureus and other gram-positive bacteria.