Of 91 compact-type strains of Staphylococcus aureus in regular serum soft agar (SSA), 82 converted diffuse-type growth in serum soft agar (pH adjusted to 6.0). With the addition of four different rabbit anticapsular sera (anti-type A, B, C, and D sera) in low pH (6.0) SSA, 21 strains of S. aureus showed compact-type colonial morphologies. Eleven, one, and one strains of S. aureus reacted singly with rabbit anticapsular sera types A, B, and C, respectively, and no strain reacted with rabbit anticapsular type D. Eight of these strains reacted with both rabbit anticapsular sera types A and B. When the ability to absorb the converting activities of the antisera (changes of colonial morphologies of anticapsular sera in SSA) was quantitatively tested, 7-to 27-fold of these organisms were capable of absorbing the activities compared with the Smith diffuse organisms. These results suggest that even unencapsulated S. aureus strains are capable of producing capsular substance, although the capability is quantitatively different from strain to strain.on August 1, 2020 by guest http://iai.asm.org/ Downloaded from

A fluorescent antibody technique was developed for the determination of the capsular‐type of strains of Staphylococcus aureus. It compared favourably with the method using serum‐soft agar (Yoshida 1972). With the new technique, many populations of encapsulated and unencapsulated strains were investigated. Of 1421 fresh isolates of Staph. aureus, 54 were encapsulated and among these 54·8% and 48·1% were mono‐ and polyvalent, respectively. Capsular‐type antigens A and B were found in 92·5% and 44·4% of strains respectively; capsular‐types C and D were found relatively infrequently. In the other group, of unencapsulated strains, capsular‐type antigen production was demonstrated in 125 out of 163 strains examined. Mono‐ and polyvalent capsular‐types (A and B antigen producing strains) comprised 77·6% and 22·4%. respectively. In these capsular‐types A and B were found in 54·4% and 62·4%, respectively: capsular‐type antigen C and D producing strains were again infrequent. These results indicate that a majority of ordinary Staph. aureus strains produce capsular‐type antigens although isolation of the encapsulated strains is infrequent.

No abstract

S U M M A R YCompact-colony forming active substance (CCFAS), the material responsible for the compact colonies of Staphylococcus aureus observed in serum soft agar, was found to be an alkaline-stable, associated polysaccharide containing galactose, N-acetylglucosamine, ribitol, phosphorus and a small quantity of alanine. This substance, when extracted from strains unable to produce protein A and clumping factor, was able to absorb the serum-reacting factor whereas a teichoic acid preparation of one strain could not. The formation of CCFAS was unaffected by the age of the cells, whereas when staphylococci were cultured at alkaline pH, young cells produced more clumping factor than old ones. Both fibrinogen and its degradation products were capable of inducing compact colonies in a strain of S. aureus. The ability of human sera to interact in compact-colony formation was independent of the immunoglobulin content. Thus neither protein A, clumping factor, nor teichoic acid participate in the CCFAS reaction.