Selection Pressure

• Find out how the environment in the mouth affects the type of bacteria that grows there
• Understand how important saliva is in maintaining oral health
• pH is the most significant selection pressure in the mouth

 

Find out what grows where and why!

The idea of selection pressures pertains to the fact that there are certain “environmental factors” that will affect what type of organisms survive in any climate. This concept of climate is relative to the oral environment where there are a number of key factors or selection pressures that will determine what type of bacteria or fungi our mouths are hospitable to.

We see this phenomenon play out with plants, wherein some plants need direct sunlight, an abundance of water and warm temperatures to survive, while others will flourish in a dry climate. Yet others will grow in dark, cold, moist environments.

In the mouth, we have the same concept of selection pressure, but the factors are different. In the oral cavity we have pressures such as saliva quantity, quality, and pH, diet, professional and home cleaning, fluoride and antimicrobial products, etc. It is these selection pressures that will determine the type of bacteria we house in our mouths. Current research has shown that of all the selection pressures we have in the mouth, pH is the most significant.

The other idea to address here, is that we used to believe that sugar availability was the key selection pressure for the overpopulation of cariogenic bacteria. We now understand that what is far more significant than the presence of sugars is the resulting drop in pH that occurs when carbohydrates are ingested. It is the low pH that occurs that favors the growth and the potential overtake, depending on the frequency and/or prolonged exposures to these low pH’s that will drive the population of the biofilm towards cariogenic strains.

“Collectively, these studies showed conclusively that it was the low pH generated from sugar metabolism rather than sugar availability that led to the breakdown of microbial homeostasis in dental plaque. This finding has important implications for caries control and prevention; the data suggest that the selection of cariogenic bacteria could be prevented if the pH changes following sugar metabolism could be reduced.”

Dental plaque as a biofilm and a microbial community — implications for health and disease, Philip D Marsh, BMC Oral Health 2006, (15 June 2006)

The following quote from the article listed outlines how we can, in turn, utilize this pH selection pressure to drive the population of bacteria with the biofilm back toward health.

“A key element of the ecological plaque hypothesis is that disease can be prevented not only by targeting the putative pathogens directly, e.g. by antimicrobial or anti-adhesive strategies, but also by interfering with the selection pressures responsible for their enrichment.”