In situ neutralisation of the antibacterial effect of 0.2% Chlorhexidine on salivary microbiota: Quantification of substantivity

Objective: To quantify the substantivity of a single 0.2% Chlorhexidine mouthwash in saliva after its neutralisation with tooth-brushing and 1% acetic acid, in order to identify the effect of Chlorhexidine substantivity in regard to the re-growing period of the salivary bacteria. Methods: Unstimulated saliva samples were collected from a group of 15 healthy individuals at baseline (BS), and then 30 s and 1, 3, 5 and 7 h after the following protocols were performed: a single sterile water mouthwash (M-WATER) (negative control), a single 0.2% Chlorhexidine mouthwash (M-0.2% CHX) (positive control) and a single 0.2% Chlorhexidine mouthwash followed by a complete and detailed tooth-brushing, and a single 1% acetic acid mouthwash (M-0.2% CHX + NP). The samples were analysed using an epifluorescence microscope in combination with LIVE/DEAD (R) BacLight (TM) fluorescence solution. Results: After the M-0.2% CHX treatment, the bacterial vitality was significantly lower than BS until 7 h (87.6 +/- 6.5% vs. 73.6 +/- 8.8%; p < 0.001). However, after M-0.2% CHX + NP, the bacterial vitality remained significantly lower until 3 h with regard to BS (81.4 +/- 3.8% us. 68.1 +/- 10.6%; p = 0.001), increasing at 5 and 7 h (no differences from BS). Conclusion: The immediate antibacterial effect of a single 0.2% Chlorhexidine mouthwash is so potent that the bacterial population needs more than 3 h to return to baseline bacterial vitality levels. The substantivity of a 0.2% Chlorhexidine mouthwash is a property that significantly increases its antibacterial activity from the first hour and contributes to extend the duration of its effect by at least double. (C) 2015 Elsevier Ltd. All rights reserved.