Assessment of Antimicrobial Susceptibility of Enterococcus Faecalis Isolated From Chronic Periodontitis in Biofilm Versus Planktonic Phase

Background: Enterococci are often associated with chronic and recurrent infectious diseases because of their antimicrobial resistance. The aim of this study is to assess antimicrobial susceptibility of Enterococcus faecalis in chronic periodontitis. Methods: Antimicrobial susceptibility was determined on 23 E. faecalis strains isolated from patients with chronic periodontitis. Ampicillin, erythromycin, gentamicin, tetracycline, triclosan, and vancomycin were prepared in two-fold serial dilution up to 8,192 mu g/mL. Enterococcal biofilm was established by a biofilm device and observed by confocal laser microscopy and scanning electron microscopy. The minimum inhibitory concentration (MIC), minimum biofilm inhibitory concentration, and minimum biofilm eradication concentration were determined by spectrophotometer at optical density(650). Results: A few patches of monolayer early biofilm were observed on the surfaces of biofilm device pegs. The colony-forming units of biofilm per peg were 1.2 x 10(3) to 1.7 x 10(4) and 0 to 20 post-triclosan treatment. The MIC50 was higher than the MIC epidemiologic cut-off for tetracycline and the MIC90 was higher than the cut-off for erythromycin and tetracycline, respectively. In biofilm, minimum biofilm eradication concentrations were extremely high for all of the drugs except triclosan. Conclusions: The E. faecalis strains of chronic periodontitis exhibited weak biofilm formation ability at the early stage. Over 50% of the strains were resistant to tetracycline, and a few strains were highly resistant to erythromycin or gentamicin. E. faecalis cells in biofilm were hardly eradicated by most of the agents, even in high concentrations. Triclosan was effective in inhibiting E. faecalis growth in both biofilm and planktonic phase. J Periodontol 2011;82:626-631.