Mechanism of Compact-colony Formation by Strains of Staphylococcus aureus in Serum Soft Agar

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Abstract
Compact-colony forming active substance (CCFAS), the material responsible for the compact colonies of S. aureus observed in serum soft agar, was an alkaline-stable, associated polysaccharide containing galactose, N-acetylglucosamine, ribitol, P 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, but a teichoic acid preparation of 1 strain could not. The formation of CCFAS was unaffected by the age of the cells, but when staphylococci were cultured at alkaline pH, young cells produced more clumping factor than old ones. 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.

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