Cytotoxic material released from Staphylococcus epidermidis. I. Effects on [3H]thymidine incorporation of human lymphocytes.

Incorporation of [3H]thymidine ([3H]TdR) into tonsil lymphocytes was inhibited by native Staphylococcus epidermidis while Staphylococcus aureus Cowan I caused stimulation. The inhibitory effect of S. epidermidis was abolished by formalin treatment but not by heat killing. A toxic agent was released from S. epidermidis on gentle water extraction without lysing the bacteria. The extract contained protein and other UV-absorbing material, but did not exhibit haemolytic, lysozyme, catalase or protease activity. The heat-resistant, formalin-sensitive inhibitor present in the aqueous extract of S. epidermidis inhibited [3H]TdR incorporation of lymphocytes in a dose-dependent manner and decreased the viability of lymphocytes.