FACTORS AFFECTING THE COLLAGEN-BINDING CAPACITY OF STAPHYLOCOCCUS-AUREUS

To determine whether the ability of Staphylococcus aureus to bind coll agen involves an adhesin other than the collagen adhesin encoded by cn a, we examined the collagen binding capacity (CBC) of 32 strains of S. aureus. With only two exceptions, a high CBC corresponded with the pr esence of cna. Both exceptions involved cna-positive strains with a lo w CBC. The first was a single strain (ACH5) that encoded but did not e xpress cna. The second were the mucoid strains Smith diffuse and hi, b oth of which encoded and expressed wa but bound only minimal amounts o f collagen. Analysis of capsule mutants suggests that the reduced CBC observed in the mucoid strains was due to masking of the collagen adhe sin on the cell surface and that this masking effect is restricted to heavily encapsulated strains. Differences in the CBC of the remaining cna-positive strains were correlated to variations in the level of cna transcription and mere independent of the number of B domain repeats in the cna gene. In all cna-positive strains other than ACH5, cna tran scription was temporally regulated, with cna mRNA levels being highest in cells taken from exponentially growing cultures and falling to alm ost undetectable levels as cultures entered the post-exponential growt h phase. The CBC was also highest with cells taken from exponentially growing cultures. Mutation of agr resulted in a slight increase in cna transcription and a corresponding increase in CBC during the exponent ial growth phase but did not affect the temporal pattern of cna transc ription. Mutation of sar resulted in a more dramatic increase in CBC a nd a delay in the post-exponential-phase repression of cna transcripti on. Mutation of both sar and agr had an additive effect on both CBC an d cna transcription. We conclude that (i) cna encodes the primary coll agen-binding adhesin in S. aureus, (ii) snr is the primary regulatory element controlling expression of cna, and (iii) the regulatory effect s of sar and agr on cna transcription are independent of the interacti on between sar and agr.