SCIENCE

Ask a Scientist: How did we get to 52% reduction in plaque?

Betty Zou, Ph D.

Dental plaque is made up of millions of bacteria that live in a sticky film on the surface of teeth. This microbial community is also referred to as a biofilm. To study the effectiveness of qii in reducing dental plaque, we tested it in the lab against the oral pathogens Streptococcus mutans (tooth decay and cavities), Porphyromonas gingivalis  (gingivitis) and Solobacterium moorei (halitosis).

METHODS

The effects of qii on single species biofilms were determined using biofilm viability assays as previously described (12). Twelve well plates were coated with saliva to allow an acquired enamel pellicle to form. S. mutans  and P. gingivalis monocultures were added and grown in sucrose-containing media to facilitate biofilm formation. Growth media and planktonic cells were removed after 24 hours of biofilm growth. qii, water or phosphate buffered saline (PBS) were added for either 15 minutes (S. mutans) or 7 minutes (P. gingivalis). The exposure times were selected based on the amount of time estimated to finish a serving of qii and optimized for bacteria-specific growth rates. Following treatments, bacterial cells were washed twice with PBS, harvested and plated out with serial dilutions to determine viable bacteria counts. PBS-treated wells served as the background to calculate percent viability following treatment.

Because S. moorei does not readily form biofilms, minimal inhibitory concentration (MIC) assays were used to measure the effect of qii of bacterial growth (34). Serial dilutions of qii were made in Schaedler’s broth with water-diluted broth serving as the control. Bacteria were added and incubated for 48 hours in an anaerobic growth chamber at 37°C before being plated out onto blood agar plates. The MIC was defined as the lowest concentration at which S. moorei growth on plates was not observed.

RESULTS

The lychee flavored qii was the most effective reducing viable bacteria counts in the S. mutans single species biofilms. Compared to the PBS control, only 48% of S. mutans survived the treatment, which means that a 15 minute exposure to lychee flavored qii killed 52% of the biofilm. Exposure to either the pomegranate or white peach flavors eliminated just under half of all the bacteria in the biofilm. That all three flavors of qii performed significantly better than water, which left 83% of S. mutans alive.

The results in P. gingivalis single species biofilm viability assays were more variable with the pomegranate flavor showing the strongest effect. As with S. mutans, all three flavors of qii were significantly better at reducing bacterial viability compared to water.

qii also exhibited a strong inhibitory effect on S. moorei growth in liquid culture. The 20% dilution of qii in Schaedler’s broth was sufficient to inhibit bacterial growth. In contrast, bacterial growth persisted at 90% dilution of water in broth, indicating that the effects of qii are not related to the lack of nutrients.

Betty Zou, Ph D.

Scientist turned science writer and communicator. I turn complex scientific concepts and studies into clear and engaging content for diverse lay audiences. Previous work include blog posts, news articles and releases, patient and customer profiles, feature length stories, donor reports and marketing materials. My areas of expertise are molecular biology, microbiology and microbiome-related topics but I have also written extensively about other health and medicine topics such as cancer, cardiology and trauma.

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