Influence of sublethal antibiotic concentrations on bacterial adherence to saliva-treated hydroxyapatite

The influence of growth in the presence of sublethal concentrations of nine antibiotics on the ability of certain potentially odontopathic bacteria to attach to saliva-treated hydroxyapatite surfaces which mimic teeth was studied. Cells of Actinomyces viscosus LY7 and S2, Bacteroides gingivalis 381, Capnocytophaga ochraceus 6, and Actinobacillus actinomycetemcomitans N27 attached in lower numbers to saliva-treated hydroxyapatite when grown in the presence of 50% of the minimum inhibitory concentration of tetracycline. Electron microscopic observations of negatively stained preparations indicated that tetracycline-grown A. viscosus LY7 cells had fewer fimbriae than did untreated cells, which may account for the impaired ability of the treated cells to attach. However, cells of Actinomyces naeslundii L13 and S4 attached in higher numbers when grown in the presence of tetracycline, clindamycin, erythromycin, chloramphenicol, or neomycin. Streptococcus mutans strains H12 and JBP also exhibited increased adherence to saliva-treated hydroxyapatite when grown in the presence of 50 or 25% of the minimum inhibitory concentration of penicillin. Thus, growth in the presence of sublethal antibiotic concentrations could increase as well as decrease the adherence of bacteria to saliva-treated hydroxyapatite. Antibiotic-grown cells of the Actinomyces strains showed enhanced hemagglutination activity, but this did not correlate with their ability to attach to saliva-treated hydroxyapatite. Sublethal concentrations of antibiotics in the growth media also affected the coaggregation reactions of several organisms; the effects were specific for one member of the coaggregation pair.