In vitro assay for the screening of the plaque-reducing activity of antimicrobial agents.

Abstract

Bacteria grown in biofilms are less susceptible to antimicrobial agents than planktonic bacteria. One of the most common biofilms in humans is dental plaque. To investigate the antimicrobial activity against dental bacteria grown in biofilms, biofilms were generated with Streptococcus sanguis on hydroxyapatite disks to mimic the tooth surface. After 48 h of aerobic incubation at 37 degrees C in a continuous flow culture, a biofilm consisting of Streptococcus sanguis became visible on the surface of the disks. The disks were removed from the growth chamber and placed in different vessels containing either chlorhexidine digluconate (CAS 55-56-1, 0.1% or 1.0%), polyvinylpyrrolidone iodine (1.5% or 7.5%), or octenidine dihydrochloride (CAS 70775-75-6, 0.05% or 0.1%) for 5 or 30 min. In addition, the antiseptics were applied to the bacterial suspension in the growth chamber. A significant difference was observed in the antimicrobial activity against bacteria in the suspension liquid compared to the bacteria grown in biofilms. The best reduction factors were obtained with chlorhexidine (1.0%, 30 min) for either sessile (3.97 Ig) or planktonic bacteria (> or = 5.58 Ig). Clear relationships between the doses and times of action were found for the assessed agents. Therefore, the authors conclude that the present in vitro assay is a quick and cost-effective model to screen the activity of antimicrobial agents against bacteria grown in biofilms.