Mouth Microbiota That “fuzzy” feeling that can be felt on un…
Mouth Microbiota That “fuzzy” feeling that can be felt on unbrushed teeth is an accumulation of a biofilm of bacteria. There are several bacteria within a person’s mouth which make up this biofilm and are cariogenic, meaning they have a tendency to cause dental caries. These include Lactobacillus acidophilus, Streptococcus mutans (and S. gordonii, S. salivarius), and Actinomyces odontolyticus. These organisms are able to ferment carbohydrates to lactic acid,thus lowering the pH at the surface of the enamel which can decalcify the enamel and lead to cavities. Enamel decalcification will begin with a pH of 5.5 and accelerates as the pH reaches 4.4. For example, S. mutans produces the enzyme dextransucrase, which polymerizes sucrose to form a polysaccharide called glucan. L. acidophilus produces a similar polymer called lexan. Glucan and lexan are both glycocalyces which bind tightly to teeth, allowing the bacteria to form a biofilm. The bacteria then produce acids as a product of carbohydrate fermentation. Please observe the stages of dental caries in the picture below: The Snyder Test is used to determine a person’s susceptibility to dental caries based on acid production that is assumed to be a result of the growth of lactobacilli on the teeth or in other areas of the mouth. (Note that the Snyder Test does not test for cariogenic streptococci or actinomycetes.) The Snyder Test agar contains 2% glucose and has a pH of about 4.8. This low pH inhibits the growth of most organisms, but it is ideal for lactobacilli. If growth occurs, and lactic acid is produced by the lactobacilli, the pH will drop below 4.8 to about 4.4. The indicator used to show this change in pH is bromcresol green, which will change from green to yellow upon acid production. The rate of change is another factor to be considered, as it is an indication of the number of acid-producing organisms present (i.e. the faster the rate of change, the more organisms present). The extent to which a culture changes color following incubation indicates a person’s susceptibility to the formation of dental caries: Alternatively, the tubes can be read at different time intervals and the amount of time it takes for the tube to turn yellow correlates with an individual’s susceptibility to dental caries:24 hours = very high susceptibility48 hours = high susceptibility72 hours = moderate susceptibility A Snyder test was performed on an individual. After 24-hours of growth, the result is shown below. What is the most likely evaluation of the person’s susceptibility to the formation of dental caries? Make sure and compare to the control tube. Negative Control Patient Sample
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