Opsonic requirements and surface hydrophobicity of novobiocin-resistant, coagulase-negative staphylococci

The opsonic requirement for phagocytosis and killing and cell-surface hydrophobicity of five strains of Staphylococcus saprophyticus isolated from clinical sources were studied. Phagocytosis and killing of bacteria by human granulocytes were measured in suspension. Bacterial aggregating cell-surface hydrophobicity was determined by salt aggregation, and the absorptive hydrophobicity was measured by hydrophobic interaction chromatography. All strains were well opsonised by pooled normal human serum 10%. Ingestion of these bacteria could be detected to a variable extent in the absence of extracellular opsonins; heat-inactivated serum 10% or intravenous IgG concentrate 1 mg/ml improved phagocytosis of all strains. Significantly increased rates of both the ingestion and killing of one of the five strains occurred in the presence of IgG or in the absence of opsonins, compared to those found with each of the other four. This particular strain had significantly stronger adsorptive surface hydrophobicity than the other four strains, and with all strains there was a correlation between hydrophobicity and phagocytosis by granulocytes in the absence of opsonins.