Staphylococcus aureus strains isolated from patients with septic arthritis or osteomyelitis possess a collagen receptor present in two forms, which contains either two or three copies of a 187-amino-acid repeat motif. Collagen receptor-positive strains adhered to both collagen substrata and cartilage in a time-dependent process. Collagen receptor-specific antibodies blocked bacterial adherence, as did preincubation of the substrate with a recombinant form of the receptor protein. Furthermore, polystyrene beads coated with the collagen receptor bound collagen and attached to cartilage. Taken together, these results suggest that the collagen receptor is both necessary and sufficient to mediate bacterial adherence to cartilage in a process that constitutes an important part of the pathogenic mechanism in septic arthritis.

The mechanisms by which oral lactobacilli, one of the three major genera of cariogenic bacteria, attach to tooth surfaces are unknown. We hypothesize that recognition of collagen, the major component of dentin, may be a mechanism which localizes these bacteria to exposed root surfaces as well as to carious lesions which have penetrated the dentin. We found that the majority of oral Lactobacillus spp. strains recognize and bind collagen type I. Binding of 125I-labeled collagen type I to two strains of L. casei rhamnosus has been characterized in some detail. These strains were previously characterized with respect to their attachment to dentin (Switalski and Butcher, 1994). The process of 125I-collagen binding was mediated via specific as well as charge interactions. The putative adhesin-mediated (specific) interaction involved a limited number of bacterial surface components (2 x 10(3)/cell). Under conditions conducive for non-specific interactions (low ionic strength), the binding was higher by an order of magnitude. Collagen binding strains were found to adhere to collagen-coated surfaces, while strains unable to bind collagen adhered to a much lesser extent. Adherence of bacteria to collagen-coated surfaces could be competitively inhibited with collagen. These interactions may target collagen-binding strains of lactobacilli to dentin collagen in the oral cavity and thus play a role in the pathogenesis of root surface and/or coronal caries. Interference with this collagen-mediated attachment of lactobacilli may provide effective means of caries control, particularly in view of the fact that other oral acidogenic microbiota also interact with collagen.

Some strains of Streptococcus mutans were found to recognize and bind collagen type I. Binding of 125I-labeled collagen type I was specific in that collagen types I and II, but not unrelated proteins, were able to inhibit binding of the labeled ligand to bacteria. Collagen binding to S. mutans was partially reversible and involved a limited number of bacterial binding sites per cell. S. mutans UA 140 cells bound collagen type I with high affinity (Kd = 8 x 10(-8) M). The number of binding sites per cell was 4 x 10(4). Collagen-binding strains of S. mutans were found to adhere to collagen-coated surfaces as well as to pulverized root tissue. S. mutans strains that did not bind the soluble ligand were unable to adhere to these substrata. Adherence to collagen-coated surfaces could be inhibited with collagen or clostridial collagenase-derived collagen peptides. Adherence of S. mutans to dentin was enhanced by collagen types I and II but inhibited by collagen peptides. S. mutans UA 140 bound significantly less 125I-collagen type I following treatment with peptidoglycan-degrading enzymes. These enzymes released a collagen-binding protein (collagen receptor) with a relative molecular size of 16 kDa. The results of this study suggest that collagen mediates adhesion of S. mutans to dentin. This interaction may target collagen-binding strains of S. mutans to dentin in the oral cavity and may play a role in the pathogenesis of root surface caries.

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