Encapsulation by transformation of strains of Staphylococcus aureus determined by the serum-soft agar technique.

Transformation for capsular-types (A and B) between four Staphylococcus aureus strains was attempted using a serum-soft agar technique to distinguish the capsular-type. DNA preparations from the Smith diffuse strain (capsular-type A) transformed strain NS58C (unencapsulated variant of capsular-type B) to type A. The strain NS58C required Ala- and His-, however, the two transformants tested were Ala+ and His+. These properties coincided with those of the donor strain just as the following characters of the transformants, which are quite different from the untransformed recipient cells: i) negative clumping factor reaction, ii) diffuse-type growth in serum-soft agar, and iii) high mouse virulence. The change to capsular-type A was antigenically comfirmed by electronmicroscopy using ferritin conjugated anti-capsular antibody.