In vitro biofilms have been developed to model the conditions in the mouth. This study compared the antimicrobial activity of three mouth rinses when tested against two different isogenic strains of Actinobacillus actinomycetemcomitans, one of which was a clinical isolate which forms tenacious biofilms and the other a planktonic form.

Three mouth rinses and a control rinse were tested.

  • Essential oils (LISTERINE®)
  • Triclosan and PVM/MA copolymer
  • Amine-fluoride, stannous fluoride (Meridol®)
  • Control: phosphate buffered saline/PBS

Briefly, the mouth rinses were tested against planktonic bacteria by exposing a standardised number of bacteria to each rinse for 15 seconds, followed by washing with sterile PBS. The mixture was then incubated on agar plates and the number of viable colonies assessed. Likewise, biofilms were grown in tissue culture flasks and exposed to each rinse for 15 seconds. The biofilm was washed with sterile PBS, and the bacteria incubated on agar plates to allow an assessment of kill rate. Each rinse was tested six times in each assay.

All 3 mouth rinses produced statistically significant 99.99% reductions (p≤0.0001) in both planktonic strains, compared to the PBS control. Effects on the biofilm forms of the organisms were more variable.

                        Kill rates (% kill) for mouth rinses versus PBS control

  Strain #1 (CU1000/CU1060) Strain #2 (NJ4300/NJ4350)
  Biofilm Planktonic Biofilm Planktonic
Control (PBS) - - - -
Essential oils (LISTERINE®) 98.2 >99.9 96.5 >99.9
Amine, stannous fluoride 20.0 >99.9 5.5 >99.9
Triclosan PVM/MA copolymer 8.0 >99.9 3.3 >99.9


Adapted from Fine et al. 2001.

From the table, it can be seen that all three mouth rinses were highly effective at killing planktonic bacteria. Only the essential oils formulation (LISTERINE®) delivered a statistically significant percentage kill versus the control rinse when tested against biofilms.

This study demonstrates the resistance to antimicrobial agents that a biofilm confers, and the difference in biofilm kill rates provided by different commercially available mouth rinses.



  1. Fine DH et al. Comparative antimicrobial activities of antiseptic mouthrinses against isogenic planktonic and biofilm forms of Actinobacillus actinomycetemcomitansJ Clin Periodont 2001; 28: 697–700.