Subinhibitory concentrations of tetracycline alter fibrinogen binding by Bacteroides intermedius

Previous studies from our laboratory have shown that a strain of Bacteroides intermedius, VPI 8944, an organism isolated originally from a patient with acute necrotizing ulcerative gingivitis, binds human fibrinogen rapidly, reversibly, specifically, saturably, and with high affinity (M.S. Lantz, L.M. Switalski, K.S. Kornman, and M. Höök, J. Bacteriol. 163:623-628, 1985). We examined the effect of growth in subinhibitory levels (sub-MICs) of tetracycline on fibrinogen binding by these bacteria and found concentration-dependent inhibition of fibrinogen binding by bacteria grown in the presence of tetracycline over the range of tetracycline concentrations from 1/64 to 1/8 the MIC. Analysis of the binding data suggests that bacteria grown in the presence of sub-MICs of tetracycline bind fewer fibrinogen molecules per cell than do bacteria grown in the absence of the drug. If fibrinogen-mediated adherence is important in the establishment B. intermedius in periodontal lesions and lesions of acute necrotizing ulcerative gingivitis, then tetracycline may be effective in disrupting establishment of these organisms at concentrations well below those required to achieve a bacteriostatic effect.