Resistance profile survey of 50 periodontal strains of Actinobacillus actinomyectomcomitans.

ABSTRACT

BACKGROUND: Antibiotic resistance has been increasingly described among bacterial species colonizing periodontal pockets, particularly in Prevotella and Porphyromonas spp. strains producing beta-lactamases, and frequently associated with resistance to tetracycline and erythromycin. These resistance genes may be carried on motile genetic elements, or transposons, capable of interspecies and intergeneric transmission among bacterial strains colonizing a same ecological niche. The aim of this prospective study was to determine the resistance profile of Actinobacillus actinomycetemcomitans and the prevalence of A. actinomycetemcomitans strains producing beta-lactamases in periodontal pockets. METHODS: Fifty strains of A. actinomycetemcomitans were isolated from 42 patients with adult periodontitis. No patient had periodontal or antibiotic therapy in the previous 6 months. Bacterial samples were collected from periodontal pockets > or =5 mm, appropriately diluted, inoculated onto selective medium (chocolate blood agar with bacitracin 75 microg/ml and vancomycin 5 microm/ml) and incubated for 5 days at 37 degrees C in air with 5% CO2. After conventional identification, susceptibility testing to 11 antibiotics was performed by the broth dilution method, in trypticase soy broth supplemented with yeast extract, hemin, and 0.1% NaHCO3 to maintain microaerophilic conditions in the microtitration plate wells by CO2 formation. RESULTS: No strain demonstrated resistance to amoxicillin, amoxicillin-clavulanic acid combination, pristinamycin, or ciprofloxacin at the breakpoint, but 40% of the strains were slightly resistant to penicillin G, and 4% were resistant to erythromycin, 90% to spiramycin, 18% to clarythromycin, 4% to tetracycline, 72% to metronidazole, and 12% to ornidazole. Amoxicillin, followed by tetracycline and erythromycin, was the most effective antibiotic on A. actinomycetemcomitans. The phenotypic research of a beta-lactamase was negative for all the strains tested. CONCLUSIONS: In this work, most A. actinomycetemcomitans strains were resistant to metronidazole, but the amoxicillin-metronidazole association may be of interest against subgingival anaerobic and capnophilic mixed flora. Pristinamycin and ciprofloxacin appeared as effective alternative monotherapies against A. actinomycetemcomitans. The threat of beta-lactam antibiotic resistance related to beta-lactamase production is currently not a problem with A. actinomycetemcomitans as it has been reported in oral anaerobes.