Serological typing of Staphylococcus epidermidis strains by the serum-soft agar technique.

Antisera to five different diffuse forms of Staphylococcus epidermidis were prepared in rabbits as a mean of serological differentiation of S. epidermidis strains. These antisera converted the growth types of the homologous strains from diffuse to compact form in serum-soft agar but did not convert the heterologous strains. The converting activities of the antisera were absorbed out with homologous organisms and not by heterologous strains, indicating the specific serological properties of these strains. Further, the converting activity was absorbable with cell surface substance extracted by sonic oscillation and was not absorbed with cells from which this surface substance had been removed. With these factor sera and the serum-soft agar technique, S. epidermidis strains were differentiated, and it was found that 102 of 116 strains or 87.9% were typable. Within the 102 typable strains, 49 and 53 typed as monovalent and polyvalent, respectively. No correlation between source and strain types of S. epidermidis was found.