title: Inhibitory effect of quercetin on periodontal pathogens.
abstract: BACKGROUND
  Periodontal disease and associated bone loss can severely hinder orthodontic treatment. Actinobacillus actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) are bacteria which are strongly associated with this type of bone loss. Quercetin, a unique flavonoid, which is found in many common foods including apples, onions and tea may have a effect against these bacteria.
  
  
  OBJECTIVE
  To study the effect of quercetin on the in vitro growth of periodontal pathogens Aa and Pg.
  
  
  METHODS
  The antimicrobial effects were determined in vitro using a broth dilution assay. Aa and Pg were grown to a density of 10(7) to 10(8) cfu/mL and subsequently incubated with test solutions of quercetin at different concentrations (0.025 g/mL, 0.05 g/mL, and 0.1 g/ mL). 0.2% chlorhexidine was used as the positive control and 0.9% sodium chloride (NaCl) as the negative control. Aliquots for the growth assay were taken as soon as the solutions were mixed, and after 1, 3, 6, and 24 hours of incubation in an anaerobic chamber for Aa and Pg. Colonies appearing on the blood agar plates were visually counted after three days for Aa and 5 days for Pg.
  
  
  RESULTS
  This study demonstrated that quercetin is a potent antimicrobial agent. When Aa and Pg were incubated with quercetin, their growth began to be inhibited at 1 hour. Aa, shows a transient inhibitory effect for 1 to 12 hours after which the antimicrobial effect gradually decreasds. With Pg, the effect increased with time and complete inhibition was achieved with concentrations of 0.1 g/mL, 0.05 g/mL and 0.025 g/mL by 24 hours. No significant difference was found between the chlorhexidine group and the quercetin solution after 24 hours of incubation.
  
  
  CONCLUSIONS
  Quercetin has an inhibitory effect on Aa and Pg.
authors.affiliation: University of Hong Kong.
authors.forename: F
authors.initials: F
authors.lastname: Geoghegan
authors.forename: V W K
authors.initials: VW
authors.lastname: Tsui
authors.forename: R W K
authors.initials: RW
authors.lastname: Wong
authors.forename: A B M
authors.initials: AB
authors.lastname: Rabie
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000187:drug effects*; D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology*; D002710:Chlorhexidine / Q000494:pharmacology; D015169:Colony Count, Microbial; D003470:Culture Media; D010510:Periodontal Diseases / Q000382:microbiology; D016966:Porphyromonas gingivalis / Q000187:drug effects*; D011794:Quercetin / Q000494:pharmacology*
chemical_list: D000891:Anti-Infective Agents, Local; D000975:Antioxidants; D003470:Culture Media; D011794:Quercetin; D002710:Chlorhexidine