Inhibition of K88-mediated adhesion of Escherichia coli to mammalian receptors by antibiotics that affect bacterial protein synthesis.

The ability of ten inhibitors of bacterial protein synthesis to decrease adhesion of Escherichia coli bearing K88ac fimbriae was examined. In the presence of the antibiotics at concentrations below the MIC values neomycin was the least effective inhibitor of adhesion and minocycline the most active. The effect of minocycline on the synthesis of individual polypeptides encoded by the K88ac determinant was examined in detail. The rate of synthesis of K88ac pilus protein in the presence of minocycline 0.75 mg/l (0.5 MIC) was less than that of total cell protein synthesis, suggesting that pilus protein becomes progressively 'diluted' in the outer membrane during exposure to this antibiotic concentration. Furthermore, the synthesis of two 'helper' polypeptides (molecular weights of 27.5 K and 27 K) which are probably involved in secretion of K88ac pilus protein through the cell envelope, was particularly sensitive to minocycline. Our observations suggest that the ability of translational inhibitors to decrease K88ac mediated adhesion probably results from direct inhibition of synthesis of fimbrial protein itself, together with inhibition of 'helper' polypeptide synthesis.