Effect of clarithromycin in the resistance profile of oral streptococci

Objective:the aim of the present study was to verify differences in the resistant-microorganisms (oral streptococci) proportion from salivary microbiota of 20 healthy volunteers, after two doses of 500mg clarithromycin. Methods: The samples were collected before and after 1.2h, 2h, 6h and 12h of drug administration, inoculated on Mitis Salivarius agar and incubated in microaerophilia during 48h. The characteristic colonies were submitted to biochemical tests for streptococci identification and antimicrobial susceptibility tests against penicillin G, amoxicillin, amoxicillin + clavulanic acid, cephalexin, cephalotine, erithromycin, azithromycin, clarithromycin, clindamycin and vancomycin. After 18h, the inhibition zones were measured and each microorganism was classified into sensible, intermediary or resistant group. Results: 113 streptococci colonies were isolated (14 S. salivarius, 7 S. mutans, 47 S. mitis and 45 S. milleri) after the first dose and 135 colonies (7 S. salivarius, 14 S. mutans, 67 S. mitis and 47 S. milleri) after the second dose. All microorganisms were sensible against cephalexin and cephalotine and one strain (S. milleri) was resistant against amoxicillin + clavulanic acid. Up to 8 strains were resistant against penicillin G, amoxicillin, clindamycin and vancomycin. Up to 9 strains were resistant against clindamycin, up to 61 strains (minimum=4) were resistant against azithromycin and up to 65 strains (minimum=6) were resistant against erythromycin. Conclusion: the penicillin group is still considered the first choice for dental procedures and the macrolide group should be not considered against streptococcal infections.