Antibiotics alter interactions of Staphylococcus aureus with collagenous substrata

The effects of sub-minimum inhibitory concentrations (sub-MICs) of three antibiotics affecting the biosynthesis of peptidoglycan on the interactions of Staphylococcus aureus strains with collagenous substrata were evaluated. In a system measuring binding of 125I-labeled collagen, growth of bacteria in the presence of one-quarter MIC of cloxacillin and vancomycin reduced the number of collagen binding sites on the surface of bacteria. Growth in the presence of cefpodoxime reduced the number of collagen binding sites in one strain and increased it in another. Cefpodoxime also increased the dissociation constant of collagen binding to bacteria, 2- to 3-fold, while the other two antibiotics did not affect the affinity of the interaction. In a system measuring adhesion of 125I-labeled bacteria to collagen-coated surfaces or cartilage, bacteria grown in the presence of cloxacillin and vancomycin attached to varying degrees depending on the strain. In contrast, compared to untreated controls as well as to bacteria treated with the other two antibiotics, growth in the presence of cefpodoxime significantly reduced adhesion of the majority of strains tested. Sub-MICs of antibiotics appear to affect staphylococcal adhesion to collagenous substrata with cefpodoxime exhibiting the strongest effect. The critical factor in reducing bacterial adhesion seems not to be the number of bacterial binding sites for collagen, but the affinity of the interaction.