Mount Holyoke Microbes: Should you feel guilTEA about your morning beverage? Recent study says “no”

Original Article: Xu X, Zhou XD, Wu CH. Tea catechin epigallocatechin gallate inhibits Streptococcus mutans biofilm formation by suppressing gtf genes. Archives of Oral Biology. 2012, 57, 678-683.

By: Hillary Detert, Alexandra Albino, and Sydney Casey

The population of the United States alone consumes an estimated 284 million cups of tea per day, generating over $15 billion dollars in sales each year (“Tea Drinking Statistics”). One of the most popular beverages in the world, tea has been used as a medical remedy for centuries. More recently, tea has been investigated in a number of scientific studies and has been shown to have positive effects on human health, with benefits that range from anti-carcinogenic properties to loose-leaf application in repairing damaged skin (“Tea Drinking Statistics”).

A recent study conducted by researchers at the University of Illinois-Chicago School of Dentistry suggests that tea may have another unexpected health benefit: preventing the accumulation of dental plaque. What we recognize simply as “dental plaque” is actually an oral biofilm--a complex network of bacteria that grow in cooperation with one another under hospitable conditions in the oral cavity. A key part of the oral bacteria community that causes dental plaque and cavities is a gram-positive bacteria known as Streptococcus mutans. These anaerobes are commonly found in the human oral cavity and work by degrading tooth enamel on a molecular level by producing glucosyltransferases (GTFs) which synthesize intra- and extracellular polysaccharides (IPS and EPS): the primary components of biofilms.

The breakdown of sugars provides energy for S. mutans and simultaneously produces an acidic environment. This subsequent lowering of oral pH, in turn, can dissolve tooth enamel and calcium molecules, resulting in holes in the teeth. S. mutans is also able to wreak havoc on the human mouth through utilizing one of its many virulence factors, all of which help S. mutans evade the intervention of the immune system. These virulence factors include: water insoluble glycans, acid tolerance, and production of lactic acid.

However, S. mutans should not always be considered a trouble-maker. Despite its capacity for virulence, S. mutans can be considered a part of our healthy oral flora so long as fermentation processes in the oral cavity are kept in-check and to a minimum (this requires very sophisticated technology: chiefly, your tooth brush!)

But, just in case your toothbrush fails you, you can be comforted by the fact that previous research has shown that deletion of GTF genes (B and C in particular) resulted in diminished biofilm formation, suggesting that suppression of the GTF genes may represent an alternative approach to disrupting biofilm formation, and as a result, tooth decay. Tea, which contains epigallocatechin gallate (EGCG), a particular kind of tea catechin, has been shown to reduce S. mutans cell adherence by suppressing the activity of GTF enzymes. However, the mechanism by which EGCG goes about doing this had yet to be fully developed. As a result, researchers at UIC College of Dentistry investigated the effect of sub-bacteriostatic levels of EGCG on the sucrose-dependent initial attachment of S. mutans to surfaces and the effect of EGCG on the transcriptional expression of S. mutans GTF B, C, D genes (B, C, and D are different variations of glucosyltransferases and each codes for a different enzyme).

In order to observe the mechanism in which EGCG reduces S. mutans biofilm formation, the researchers used three main research methods: 1. Sucrose-dependent initial attachment assays, 2. Bacterial aggregation assays, and 3. quantitative real-time PCR, a technique that monitors the amplification of a target DNA molecule in real-time as opposed to at the end during typical PCR . The purpose of the sucrose-dependent initial attachment assays was to visualize the levels of biofilm attachment over a period of four hours when grown in varying concentrations of EGCG. The bacterial aggregation assays were done to determine that the reduction in biofilm formation was not due to bacterial aggregation, which is another known function of tea catechins. Lastly, quantitative real-time PCR was used to determine the levels of GTF B, C, and D genes expression in the presence of EGCG vs. a control of no EGCG. The experimental data shows that EGCG below the minimum growth inhibitory concentration was able to inhibit the attachment and subsequent formation of S. mutans biofilm on teeth.

Figure 1A is shows the development of S. mutans biofilm over the course of four hours in the presence of varying levels of EGCG concentrations* (control indicates S. mutans grown without EGCG). As the concentration of EGCG increases, the less confluent the biofilm becomes over time. EGCG does so by suppressing the expression of GTF genes B, C, and D.

*It is worth noting that the concentrations of catechins used in this experiment are up to three orders of magnitude smaller than what you will find in your average cup of tea.

In order to determine if the effect was a result of EGCG suppressing the genes and not forming aggregates, another known effect of tea catechins, Xu et al. performed a bacterial aggregation assay. The bacterial aggregation showed that the concentrations necessary to promote cell aggregation were twice that of those used in the study and, as a result, the data seen was not a result of aggregation.

Figure 3 shows the expression levels of GTF genes B, C, and D when exposed to EGCG concentrations below the minimal inhibitory concentration and their expression levels when no EGCG was added. The results show a significant decrease in expression of GTF genes, suggesting that EGCG suppresses their expression.

But what effect should this study have on your daily routine? If you are already an avid fan of a good cup of green tea in the morning, perhaps none at all. As long as you don’t throw in milk and sugar. A spoonful of sugar may make the medicine go down, but it will certainly not make the level of biofilm growth in your mouth (which is dependent on sucrose and promotes S. mutans to aid in tooth decay) go down.

Although this study shows that green tea can be beneficial in preventing growth of S. mutans biofilms that promote tooth decay, more research will need to be done to fully understand the effect of salivation on catechin concentration overtime. There is no guarantee that this beneficial effect of tea consumption will hold up over a long period of time if you are going about your normal routine of salivating, eating, or drinking other beverages. One way that researchers might be able to test the role of salivation on catechin concentrations could be to observe the levels of gene expression present during a variety of salivation conditions. This would be very similar to the procedures the researchers utilized in figure 3.

However, enjoying a cup or two of tea throughout the day couldn’t hurt and may even make for a more pleasant trip the next time you visit your dentist.

Next week’s feature:

Is there also an undiscovered correlation between tea consumption and level of awesome?