Variation in the size of the repeat region of the fibrinogen receptor (clumping factor) of Staphylococcus aureus strains.

The ability of Staphylococcus aureus to bind to fibrinogen and fibrin is believed to be an important factor in the initiation of foreign body and wound infections. Recently, the gene encoding the fibrinogen receptor (clumping factor, ClfA) of S. aureus strain Newman was cloned and sequenced. The ClfA protein possesses a highly unusual 308 residue dipeptide repeat region composed predominantly of Asp and Ser. Polymerase chain reaction analysis of seven different strains showed that the size of the clfA repeat coding region varies from 580 bp to 1320 bp. In contrast, the clfA region A is the same size in each strain. The size of the clfA repeat region did not correlate with the ability of these strains to form clumps in a solution of fibrinogen. Indeed, the strain with the smallest repeat size of 580 bp clumped almost as well as strain Newman. Each strain of S. aureus examined contained several high molecular mass proteins that reacted with anti-ClfA region A antibody. In some cases the molecular mass of the major protein varied in accordance with the length of the coding sequence for the repeat region R.