The relationship between phagocytosis and intracellular killing of Staphylococcus aureus by bovine neutrophils
Williams MR., Craven N., Field TR., Bunch KJ.
Neutrophil (PMN) function was compared in different cows by tests of phagocytosis, total bacterial kill, intracellular survival of Staphylococcus aureus and also by luminol-dependent chemiluminescence (CL) during phagocytosis of preopsonized zymosan. Phagocytosis was estimated by direct counts of extracellular survivors after differential sedimentation of PMN and also derived from measurement of intracellular survivors after treatment with lysostaphin. This treatment eliminated bacteria which adhered to the surface of PMN or which sedimented on centrifugation. The results obtained by the two methods were found to be highly correlated. The estimates of total bacterial survival were highly correlated with both phagocytosis and intracellular survival of Staph. aureus (P < 0·01). PMN from cows with a high rate of phagocytosis generally killed internalized Staph. aureus more efficiently. When the ratio of bacteria to PMN was increased from 1:3 to 11:3, the number of phagocytosed bacteria increased proportionately but intracellular killing was impaired. Therefore increased phagocytosis per se did not stimulate intracellular killing of Staph. aureus. Intracellular survival but not phagocytosis of Staph. aureus was also correlated with reduced CL by bovine PMN. This implies that oxidative pathways are required for the efficient destruction of Staph. aureus. © 1985.