Alteration of fimbriation and cell hydrophobicity by sublethal concentrations of tetracycline

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Abstract
The effect of growth in the presence of sublethal concentrations of tetracycline on the extent of fimbriation and surface hydrophobicity of strains of Actinomyces viscosus and Bacteroides gingivalis, two species frequently isolated from patients with rapidly progressing periodontitis, was determined. Negatively‐stained cells of A. viscosus strains LY7 and S2 and B. gingivalis strain 381 showed a dramatic reduction in the number of fimbriae on their surface when grown in the presence of 50% of the minimum inhibitory concentration of tetracycline as compared to untreated controls. Similar observations were made with fixed, lanthanum‐stained thin sections. In addition to long fimbriae, the A. viscosus strains possessed stubby, densely staining tufts on their surface which were not affected by tetracycline. The hydrophobicity of antibiotic‐grown A. viscosus and B. gingivalis cells was also found to be significantly reduced. The decrease in fimbriation and surface hydrophobicity of A. viscosus and B. gingivalis when grown in the presence of low concentrations of tetracycline may explain their reduced ability to attach to experimental pellicles. These observations suggest that part of the efficacy of tetracycline therapy for destructive forms of periodontal diseases may be mediated by an alteration of the adhesive properties of subgingival bacteria which affected their colonization.