Increased Sensitivity to Phagocytosis ofStaphylococcusE-46 after Growth in Artificial Media

Abstract

Staphylococcus E‐46, which exhibits high virulence in mice mainly due to resistance to phagocytosis, gradually lost its virulence during growth in artificial media [Heart‐Infusion (HI) slants]. Staphylococcus E‐46 is coagulase‐negative and DNase‐positive, and has a capsule‐like structure, and the less‐virulent derivative (LVD) strain seemed not to be changed in this respect. The bacteria which had been exposed to HI slants for more than one year (=LVD strain) became more sensitive to phagocytosis by mouse peritoneal macrophages than bacteria which were kept in a lyophilized state. The chemiluminescent response of macrophages to the LVD strain was remarkably higher than that to the original Staphylococcus E‐46. When the LVD or the sera for opsonization were heated, the chemiluminescence to the LVD was as low as that to the original Staphylococcus E‐46. Polyacrylamide gel electrophoresis of sonication‐released membrane protein from the LVD strain showed a unique band with a molecular weight of about 40,000. The factor concerned with the virulence of Staphylococcus E‐46 is discussed based on these results.