Abstract
Test organisms used in the present study consisted of two strains of staphylococci isolated and identified inthis laboratory, Staphylococcus aureus 131-1 and Staphylococcus aureus 125-3, and, as reference organism, Staphylococcus aureus 209 p was collaterally used. Visual observation was made on the formation of diffuse and compact types colonies which the test organisms developed on the rabbit serum-soft agar, and special attention was directed to the investigation on the characteristics of capsular strains of those organisms that formed the diffuse type colony in the medium. Study was further eytended to the distribution of both types colonies which developed on the rabbit serum soft agar from one hundred strains of staphylococci isolated from oral infections. The clumping factor was also studied with relation to the organisms forming the compact type colony. Results obtained are summarized as follows. 1) Distribution of the compact type colonies and diffuse type colonies developing in the rabbit serum soft agar from 100 strains of staphylococci was respectively 85 with the former and 15 with the latter. 2) With use of the rabbit IgG soft agar as culture medium, occurrence of the compact type colonies amounted to 74 and that of the diffuse type colonies 26. 3) When the rabbit IgM soft agar was used as culture medium, whole 100 strains of staphylococci produced the diffuse type colonies without a single colony of compact type. 4) Occurrence of the compact type colony of staphylococcus in the serum-soft agar was presumed to have a positive correlation with some antigen-antibody reaction taking place between the rabbit IgG and protein A produced by the bacterial cell body. 5) When the 15 strains of cells which formed the diffuse type colonies in the rabbit serum-soft agar were transferred to the nutrient plate agar there to form colonies, 5 strains formed sticky colonies and 2 strains formed colonies of capsule-bearing cells, and no significant relation was noticed between both groups. 6) Animal experiments showed that the capsule-bearing strains of staphylococci were more virulent than non-capsular strains in producing the kidney abscess in mice.
