In vitro-efficacy of chlorhexidine against periodontopathogenic bacteria within a multispecies-biofilm

Objective: Most in vitro-studies about the activity of antimicrobials focus on single bacterial strains in a planctonic stadium. The purpose of our study was first to establish a simple in vitro model of a subgingival biofilm consisting of four species within a flow system. Furthermore the efficacy of chlorhexidine (CHX) in concentrations and exposure times relevant in in vivo-conditions was to be tested. Methods: Preliminary tests showed that antagonistic effects between the bacterial strains had to be considered. So Porphyromonas gingivalis ATCC 33277 and Streptococcus sanguinis ATCC 10556 were replaced by the clinical isolates S. sanguinis J108a/02 and P. gingivalis D5-2-2. Finally slides were covered with artificial saliva for 1 h. Broth cultures of the bacterial strains S. sanguinis J108a/02, Fusobacterium nucleatum ATCC 25586, Actinomyces viscosus ATCC 15987 and P. gingivalis D5-2-2 had been prepared and were given time-dependent into the flow chamber. After 6 h chlorhexidine varnishes in the concentrations 0.06 %, 0.06 % + fluoride (Chlorhexamed, GlaxoSmithKline), 0.1 %, 0.2 %, 1 % were added for 30 and 60 s. The efficacy of a 1% gel (Chlorhexamed GEL 1 %, GlaxoSmithKline) was also tested. Results: Without any addition of an antimicrobial all bacterial strains were detectable in the biofilm. CHX varnishes in a concentration of 0.1 % were able to kill all bacteria after an exposure time of 60 s, also 0.06 % CHX + fluoride removed all viable bacteria. Contradictory after application of CHX-gel all bacterial strains had been found in low numbers. SEM-photographs confirmed the results. Conclusion: The in vitro model using a simple flow chamber is suitable for testing antimicrobials. Chlorhexidine has a good antibacterial efficacy against bacteria within a biofilm. Our in vitro results indicate a usage of a varnish containing a low concentration of chlorhexidine and an exposure time of 60 s.