The effect of chlorhexidine on Streptococcus sanguis biofilms.

The bactericidal effect of chlorhexidine on Streptococcus sanguis biofilms was investigated and compared with its effect on suspensions of the organism. The biofilms were found to be more resistant to the bactericidal effects of chlorhexidine than the bacterial suspensions in terms of the number of surviving organisms. The minimum inhibitory concentration (MIC) being 25 and 50 micrograms/ml, respectively, for the suspension and the 24 h biofilm. The age of the biofilm had a marked effect on the number of bacteria surviving. Older (72 h) biofilms tended to be more resistant to chlorhexidine than younger (24 h) ones, with the MIC being 200 and 50 micrograms/ml, respectively. Addition of blood to the test system greatly reduced the bactericidal effect of the chlorhexidine, increasing the MIC for the 24 h biofilm from 50 to 200 micrograms/ml.