IN-VITRO ANTIMICROBIAL SUSCEPTIBILITY OF PERIODONTOPATHIC ACTINOBACILLUS-ACTINOMYCETEMCOMITANS TO ROXITHROMYCIN AND ERYTHROMYCIN

The in vitro minimal inhibitory concentrations (MIC) and minimal bacte ricidal concentration (MBC) of roxithromycin and erythromycin against Actinobacillus actinomycetemcomitans were evaluated. Sixty-seven diffe rent A. actinomycetemcomitans isolated from periodontal pockets of 101 subjects with different forms of early-onset and adult periodontitis and three reference strains of A. actinomycetemcomitans (ATCC 29522, A TCC 29523, and NCTC 9710) were included in this study. Erythromycin sh owed poor in vitro activity against A. actinomycetemcomitans; roxithro mycin, on the contrary, exhibited good in vitro activity. Moreover, ro xithromycin showed the best in vitro antimicrobial activity against 17 serotype a and 12 serotype c subpopulations of A. actinomycetemcomita ns; against 38 serotype b subpopulation of A. actinomycetemcomitans, r oxithromycin was consistently active. Roxithromycin exhibited MBC valu es usually equal to, or onefold higher than MIC values. All the MBC va lues of erythromycin were three-to four-fold higher than the respectiv e MIC result. Since roxithromycin is characterized by high concentrati ons in serum and good penetration and diffusion into gingival tissue, it could be expected to pass into the gingival crevicular fluid at lev els sufficiently high to inhibit A. actinomycetemcomitans in vivo. The se data indicate that roxithromycin might be a potential candidate for therapeutic trials in patients with A. actinomycetemcomitans-associat ed periodontitis.