The Relationship of Capsular-type of Staphylococcus epidermidis to Virulence and Induction of Resistance in the Mouse

Biochemical, immunological and morphological properties of mouse virulent Staphylococcus epidermidis strains ATCC-31432, SE-360 and SE-10 isolated from clinical specimens were compared. Heat-killed organisms and cell surface polysaccharides extracted from cell surface fractions induced resistance in mice only against challenge with the homologous strain. Hyperimmune rabbit serum prepared with these strains passively protected mice against challenge infection only with the homologous strain. Protective activity in immune sera was absorbed by homologous whole cell and cell surface polysaccharide, but not by heterologous organisms and cell surface polysaccharide. In agar diffusion tests, cell surface polysaccharides from strains ATCC-31432, SE-360 and SE-10 produced single precipitin lines only with the homologous antiserum. The outermost layer of ultra-thin sections of the three strains was labelled by homologous but not by heterologous ferritin-conjugated serum. Biochemical analysis of the cell surface polysaccharides showed that they were composed of hexosamine, glycerol, phosphorous, alanine, glycine and phenylalanine. The three strains ATCC-31432, SE-360 and SE-10 were regarded as different from each other. Thirteen of 300 fresh isolates of Staph. epidermidis randomly selected from human clinical specimens proved to be virulent for mice. With ATCC-31432, SE-360 and SE-10 tentatively designated as capsular-type I, type II and III, respectively, a majority of mouse virulent strains belonged to capsular-type II.