Effect of a neutralising agent on the evaluation of the antimicrobial activity of chlorhexidine on the bacterial salivary flora

Abstract

Objective To test the efficacy of a previously described neutralising agent to counteract any antimicrobial activity of 0.2% of chlorhexidine (CHX) mouthrinse on the salivary flora, which is only exhibited after sampling of surviving bacteria, resulting in false positive efficacy data. Methods Unstimulated salivary samples were collected of 20 volunteers under basal conditions and at 30 s and 1 h after of a single mouthrinse of 0.2% CHX. Each salivary sample was divided into 2 equal aliquots; one was mixed with neutralising agent (3% Tween 80, 0.3% lecithin and 0.1% cysteine) and the other with a control solution. The colony forming units (cfu/mL) were determined and expressed as logarithms (log 10 cfu/mL). Results At baseline, the total bacterial concentrations were similar, independently of the addition of neutralising solution or control solution (8.419 ± 0.346 log 10 cfu/mL and 8.462 ± 0.474 log 10 cfu/mL, respectively, p = 0.440). At 30 s performing the CHX mouthrinse, the bacterial load reduction was statistically significant between both sampling methods (1.917 ± 1.275 log 10 cfu/mL, p < 0.001). One hour after performing the CHX mouthrinse, the bacterial load reduction was statistically significant between both sampling methods (0.537 ± 0.706 log 10 cfu/mL, p = 0.003). Conclusions Neutralising agent was not toxic to the bacterial salivary flora and effectively deactivated the “residual antimicrobial activity” of the 0.2% CHX (after exposure and during processing of samples). We propose the use of this neutralising agent when evaluating the antibacterial activity of CHX mouthrinses.