ANTIBIOTICS ALTER INTERACTIONS OF STAPHYLOCOCCUS-AUREUS WITH COLLAGENOUS SUBSTRATA

The effects of sub-minimum inhibitory concentrations (sub-MICs) of thr ee antibiotics affecting the biosynthesis of peptidoglycan on the inte ractions of Staphylococcus aureus strains with collagenous substrata w ere evaluated. In a system measuring binding of I-125-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 su rface of bacteria. Growth in the presence of cefpodoxime reduced the n umber of collagen binding sites in one strain and increased it in anot her. 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 adh esion of I-125-labeled bacteria to collagen-coated surfaces or cartila ge, bacteria grown in the presence of cloxacillin and vancomycin attac hed to varying degrees depending on the strain. In contrast, compared to untreated controls as well as to bacteria treated with the other tw o antibiotics, growth in the presence of cefpodoxime significantly red uced adhesion of the majority of strains tested. Sub-MICs of antibioti cs appear to affect staphylococcal adhesion to collagenous substrata w ith cefpodoxime exhibiting the strongest effect. The critical factor i n reducing bacterial adhesion seems not to be the number of bacterial binding sites for collagen, but the affinity of the interaction.