Stimulation of the phagocytic response of human phagocytes depends on the surface properties of bacteria. We studied what properties of Streptococcus pyogenes stimulate a phagocytic reaction, focusing on hydrophobicity and the Fc receptor. From Fc receptor-positive hydrophobic parent streptococcus, hydrophilic mutant and Fc receptor-deficient mutants were isolated. The mutant and parent strains were tested for stimulating activity for phagocytosis by measuring the chemiluminescence (CL) response of human phagocytes. The phagocytic response caused by the hydrophilic strain was significantly lower than that of the hydrophobic parent; while no difference in the stimulation of the phagocytic response was observed between Fc receptor-positive and -negative strains. These results showed that the hydrophobicity of the cell surface is responsible for the stimulation of the phagocytic response
