In vitro antimicrobial susceptibility of Porphyromonas gingivalis to azithromycin, a novel macrolide.

The in vitro antimicrobial susceptibility of Porphyromonas gingivalis to azithromycin, a new macrolide antibiotic of a new class known as azalides, was investigated by the agar dilution method on Brucella agar. Eighty-two P. gingivalis strains, 79 recent oral isolates, 1 nonoral isolate and 2 reference strains were included in the study. Azithromycin was highly effective against P. gingivalis. All strains were inhibited at 1.0 microgram/ml of azithromycin or less. The minimal inhibitory concentrations were 0.25 microgram/ml for 50% and 0.5 microgram/ml for 90%. These in vitro data as well as the favorable pharmacokinetics of azithromycin indicate that this new oral macrolide might be a good candidate for future clinical trials aiming to eradicate P. gingivalis from refractory periodontitis.