In vitro activity of amoxicillin, clindamycin, doxycycline, metronidazole, and moxifloxacin against oral Actinomyces.

Actinomyces spp have been increasingly associated with endodontic infections. However, the antimicrobial susceptibility of this genus has not been studied extensively. The objective of this study was to determine the susceptibility of oral isolates of Actinomyces naeslundii, Actinomyces gerencseriae, Actinomyces israelii, Actinomyces viscosus, and Actinomyces odontolyticus to amoxicillin, clindamycin, doxycycline, metronidazole, and moxifloxacin using in vitro assays. The minimum inhibitory concentration (MIC) of each bacterial isolate was determined by using E-test strips (AB Biodisk, Solna, Sweden). The MIC(90) was 0.19 microg/mL for amoxicillin, 0.25 microg/mL for doxycycline, 0.50 microg/mL for moxifloxacin, and 1.00 microg/mL for clindamycin. However, metronidazole was not active against any of the Actinomyces spp tested (MIC(90)>256 microg/mL).