title: Does human saliva decrease the antimicrobial activity of chlorhexidine against oral bacteria?
abstract: BACKGROUND
  Several studies have shown the antibacterial effectiveness of 0.2% chlorhexidine (CHX) in both in vitro and in vivo studies. In this way, CHX comes directly in contact with saliva. This in vitro study aimed at investigating the possible neutralizing effect of saliva on CHX.
  
  
  METHODS
  Saliva samples (12 ml) were collected from twenty healthy volunteers. The aerobic and anaerobic bacterial counts in saliva were determined on Colombia blood agar (CBA) and yeast cysteine agar (HCB), respectively. Saliva from each subject was divided among 4 experimental groups (3 ml/group). Samples were centrifuged at 4000 g for 10 min. The centrifuged salivary bacteria were incubated with the following solutions: 0.2% CHX in saliva, CHX in saliva with 7% ethanol, CHX in 0.9% NaCl, CHX in 0.9% NaCl with 7% ethanol. After exposure for 1 min or 3 min to these CHX solutions, the CHX was neutralized and the bacteria were cultivated, after which the number of colony forming units (aerobic and anaerobic) was determined.
  
  
  RESULTS
  CHX reduced the CFU in all groups significantly (p = 0.0001). Therefore, CHX had a similar effect on both aerobic and anaerobic microorganisms. Significantly more bacteria survived the effect of CHX when kept in salivary solution. This effect from saliva could be compensated by the addition of ethanol. In the absence of saliva there was no significant difference observed in the effectiveness of CHX with respect to ethanol. Prolonging the exposure time to 3 min enhanced the effectiveness of CHX.
  
  
  CONCLUSIONS
  The effect of saliva on the antimicrobial activity of CHX was weak albeit statistically significant. However, addition of 7% ethanol compensates this effect. The impact of saliva on the reduction of the antimicrobial efficacy of mouthrinses such as CHX needs to be taken into consideration with regard to improving their antibacterial properties.
authors.forename: Thaer
authors.initials: T
authors.lastname: Abouassi
authors.forename: Christian
authors.initials: C
authors.lastname: Hannig
authors.forename: Katja
authors.initials: K
authors.lastname: Mahncke
authors.forename: Lamprini
authors.initials: L
authors.lastname: Karygianni
authors.forename: Martin
authors.initials: M
authors.lastname: Wolkewitz
authors.forename: Elmar
authors.initials: E
authors.lastname: Hellwig
authors.affiliation: Department of Operative Dentistry and Periodontology, Albert Ludwigs University, Freiburg, Germany. ali.al-ahmad@uniklinik-freiburg.de.
authors.forename: Ali
authors.initials: A
authors.lastname: Al-Ahmad
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D001419:Bacteria / Q000187:drug effects*; D002710:Chlorhexidine / Q000627:therapeutic use*; D015169:Colony Count, Microbial; D006801:Humans; D009055:Mouth / Q000382:microbiology*; D012463:Saliva
chemical_list: D000900:Anti-Bacterial Agents; D002710:Chlorhexidine