ADHESION PROPERTIES OF MUTANTS OF STAPHYLOCOCCUS-AUREUS DEFECTIVE IN FIBRONECTIN-BINDING PROTEINS AND STUDIES ON THE EXPRESSION OF FNB GENES

Staphylococcus aureus 8325-4 has the potential to express two distinct cell wall-associated fibronectin-binding proteins called FnBPA and Fn BPB. In order to test if both proteins are expressed in S. aureus and if both are required for promoting bacterial adhesion to fibronectin-c oated surfaces, insertion mutations were isolated in each gene. A DNA fragment encoding tetracycline resistance was inserted into fnbA and a fragment encoding erythromycin resistance was inserted into fnbB. A d ouble fnbA fnbB mutant was also constructed. The fnbA and fnbB single mutants showed no significant reduction in their adhesion to polymethy lmethacrylate coverslips that had been coated in vitro with fibronecti n. However, the double mutant was completely defective in adhesion. Mo nospecific antibodies directed against the non-conserved N-terminal re gions of both proteins confirmed the lack of expression of FnBPs in th e mutant strains. Wild-type fnbA and fnbB genes cloned seperately on a multicopy plasmid were each able to restore fully the adhesion-defect ive phenotype of the 8325-4 fnbA fnbB mutant. This demonstrates that b oth fnb genes are expressed in S. aureus and that both contribute to t he ability of strain 8325-4 to adhere to fibronectin-coated surfaces, The double mutant was also defective in adhesion to coverslips that ha d been removed from tissue cages implanted subcutaneously in guinea-pi gs, which suggests that fibronectin is important in promoting attachme nt of S. aureus to biomaterial in vivo.