Mouths and Microbes

What are dental caries?

“Caries” is just a fancy name that refers to what we call“cavities. Cavities are a rotted or decayed portion of the teeth that can be minor or severe, reaching even to the tooth’s core and roots.

What causes these caries?

Caries result from plaque build-up.As plaque accumulates, acids are released and tooth material becomes degraded.This is tooth decay.Decay is not exclusive to visible parts of one’s teeth.This plaque, and its subsequent decay, can occur even at the roots and extend to the bones of the jaw.

So what is plaque?

Ready for this?That “fuzzy” feeling that can be felt on poorly brushed teeth is an accumulation of bacteria.These bacteria—Lactobacillus acidophilus, Streptococcus gordonii, Streptococcus salivarius, and especially Streptococcus mutans—are found naturally in the mouth and love to feed on carbohydrate particles that we eat.If you eat a candy bar, the sugary particles coat your mouth’s surfaces, causing these bacteria to believe that they are at an all-you-can-eat buffet.As bacteria feed on these carbohydrates, they release chemicals that attach them to the teeth.Then more and more bacteria accumulate until a visible collection of bacteria is created.This pathogenic blob then excretes acids (due to its sugar fermentation) and teeth, beginning at the enamel, become damaged.Although this is a basic universal process, the rate of tooth decay varies with the individual.Some people have bacteria that produce acid at a lower rate than others.In addition, composition of bacterial species varies by the person and even by the tooth.

Ooh, so tell me more about these bacteria…

Here are just a few of the plaque-forming microbes in the human mouth…

Lactobacillus Acidophilus

Presence of this bacteria can be detected by using the Snyder’s test, outlined on this website.These are suited to more acidic environments than most other oral bacteria can tolerate.

Streptococcus gordonii

This round strand-linked bacteria ferments sucrose and high fructose corn syrup equally well.Sucrose is the sugar of pure table sugar.It is popular for baking and sweetening drinks.High fructose corn syrup is a substitute for sucrose that can be found in nearly all U.S.-produced soft drinks and candy bars.

Streptococcus salivarius

This species is similar to others listed here in that it is Gram +, round in shape, and chain-forming.Human body temperature is about 37*C, warm enough for this microbe to survive; é will not live at 10`C.It can ferment glucose, sucrose, and usually lactose.

Streptococcus mutans

This bacterium is the “poster child” for “big, bad” destructive oral bacteria.

S. mutans is a coccoidal, Gram + , short chain-forming bacteria that enhances its growth in an anaerobic environment.It can ferment glucose, lactose, and especially sucrose.Less growth results from exposure to high fructose corn syrup, although metabolism of this sugar does occur.Adherence of S. mutans is made possible by glycosyl transferase, dextran binding proteins and dextransucrase, among other proteins and enzymes.Lactic acid is produced from its sugar fermentation, and fortunately for the bacteria, it has an effective system to reduce the effects of a low pH.To protect its colonies, S. mutans produces IgA-1 proteases and mutacins that cleave host IgA immune cells and inhibit competitor Gram + bacteria, respectively.

For more information about dental disorders, their prevention and their treatment, check out the links below!


Periodontal Disease


Bad Breath (Halitosis)

Composite vs. Amalgam Fillings

Tooth Bleaching

Ceramic Tooth Restoration

Lab Summary

Tooth Staining


Adam Goldberg

Lindsay Kirby

Leena Kulkarni

Alan Ralph

Hong Yu