User:DiekhoffB

Classification

Higher order taxa

Bacteria (Domain); Firmicutes (Phylum); Bacilli (Class); Lactobacillales (Order); Streptococcaceae (Family)

Species

NCBI: Taxonomy

Streptococcus mutans

Description and significance

S. mutans was discovered in 1924 by a man named JK Clark, whom was studying dental caries at the time of discovery. The bacterium was withdrawn from a patient's decaying tooth, observed, and described by Clark (4). S. mutans is a Gram positive bacteria that possesses anaerobic capabilities and is non-motile (2). These bacteria reside in the mouths of humans and have not been found elsewhere, although there are other species of streptococci that have been found to live in the mouth of other organisms. S. mutans also produces acid, which allows it to break down the enamel on teeth in order to dig into them. S. mutans can affect health beyond the mouth, though. Poor dental hygiene allows for the bacterium to easily break down teeth with no set backs, resulting in lower health of the body as a whole. Plaque made by S. mutans can enter the bloodstream to harden artery walls, and loss of teeth and development of gum disease can affect one's diet (6). If the teeth are not taken care of and cavities are not prevented, S. mutans can inflict a huge amount of damage.

Genome structure

The genome of S. mutans includes 2,030,936 base pairs total (1). To contain these base pairs, the bacterium possesses three separate chromosomes comprised of DNA in a circular form. In this sequence of base pairs in the chromosomes, the bacterium's ability to survive in the mouth is evident. About 15% of the genome is comprised of sequences that code for transport pathways for its different metabolic pathways (1). Because of its ability to continue metabolism without oxygen, the genome includes sequences for multiple metabolic pathways. In addition, the bacterium is able to break down a myriad of carbohydrates due to its large number of enzymes encoded in its genome. This allows for the bacterium to outcompete many of the other bacteria in the mouth.

Cell structure and metabolism

S. mutans is a facultative anaerobe, which means it can undergo metabolism in aerobic conditions, but if oxygen is not present, it is able to change pathways to anaerobic respiration (7).

A unique quality of the cell wall of S. mutans is that it lacks antigens for B cells of the body's immune system (5). This means that it is undetectable by the B cells of the immune system, allowing it to survive more easily in the mouth of humans.

S. mutans' main pathway of metabolism involves the breakdown of carbohydrates ingested through the food of the human host in which it lives. It is believed that S. mutans has the ability to metabolize more types of carbohydrates than any other Gram positive bacterium (1). This is due to its expansive genome encoding for multiple transport pathways. The final products of these pathways are normally acidic molecules such as lactic acid, ethanol and acetate (1) . These are the agents that allow the bacterium to breakdown teeth.

Ecology

Being a bacteria that causes cavities, S. mutans dwells in the mouths of humans where it creates plaque. The amount of S. mutans in the human mouth ranges from about 30 - 60% of the total bacteria present on all surfaces in the mouth (3). This bacterium often outcompetes the rest of the mouth dwelling bacteria, due to its versatility, but other species of streptococcus are seen to cause dental caries along with S. mutans. S. mutans also possesses the ability to create a polysaccharide called dextran, which is a sticky molecule (8). This allows the bacterium to adhere to the surface enamel in order to prevent washing away by saliva, the tongue, and general movement. This bacterium thrives off of the sugars from the food humans ingest and the warm temperature of the mouth is an ideal number for the bacterium to undergo metabolism and replication. Salivary glands continually wash S. mutans and all other bacteria from the mouth naturally, and this process is aided by regular teeth brushing. Absence of dental hygiene and a dry mouth give the bacterium a perfect opportunity to do damage to the teeth because they are not being removed form the tooth surfaces, but being left to produce acid and seep into the inner tooth. S. mutans' anaerobic capabilities also give it an advantage over other bacteria, as it is able to grow in deep lesions in the mouth where oxygen is low or absent in addition to aerobic regions of the mouth such as tooth surfaces. These environments are ideal as competition is low, the temperature (35-37 degrees Celsius) and pH (6.5-7.5) are optimum, and nutrient levels are high (3).

Pathology

S. mutans is a bacteria of the normal flora of the mouth, which undergoes natural processes that create acid and the breaking down of teeth and bone. In addition to dental caries, S. mutans can lead to gum disease and periodontitis (3). Both of these involve the inflammation and recession of the gums, which then leads to teeth loss. Generally, teeth loss can lead to a speech impediment and under-nutrition of an individual. Essentially, lack of proper dental hygiene does not stop its harmful effects at the mouth, but affects the entire body. S. mutans, along with other mouth dwelling bacteria, can cause this process to occur. This bacterium also does very well in individuals who consume high amounts of sugar, specifically through sodas and sticky sweets that tend to remain in the mouth for extended periods of time.

The effects of S. mutans can normally be caught before a tooth is lost by a dentist. A dentist is able to see decay indicated by brown spots on a tooth, or by feeling soft spots on teeth with a dental pick. Depending on how long the bacterium has been working, the patient may or may not feel pain or sensitivity to hot and cold even if the doctor can see a cary beginning to form. If the bacteria has eaten a large amount of the tooth, a synthetic crown will be fabricated to cover the rest of the tooth and prevent further decay after cleaning. If the tooth is beyond being able to be crowned, it will be removed and other possibilities like an implant or bridge can be used to fill the gap left by the works of S. mutans.

Current Research and/or Application to Biotechnology

Because S. mutans is a main bacteria that breaks down teeth to cause dental caries, many scientist have attempted to create a vaccine in order to eliminate it from the natural flora of the mouth. A vaccine was created in the late 80's which worked well in eliminating the bacterium from the visible surfaces of the mouth, but not very well in the crevices between teeth (4). These between teeth surfaces are highly important to keep clean and bacteria free. The vaccine was not able to do this due to the lack on contact of blood vessels to the crowns of teeth and the lack of saliva contact in these spaces, preventing the vaccine from acting on the bacterium. Along with poor performance from a biological standpoint, the economics of the vaccine were also impractical. The vaccines are very expensive compared to regular dental hygiene, such as brushing teeth, flossing and using mouthwash (4). While dental hygiene does not completely eliminate the bacterium, it does prevent the formation of caries if done routinely.

Additionally, many naturally occurring minerals and substances function as a natural antibiotic or reverse the damage of S. mutans on the surface of teeth. One of these substances being green tea. The chemical make up of green tea includes a molecule called polyphenol, which prevents the bacterium from utilizing the sugar in the mouth from ingested foods (3). This does not allow the bacteria to undergo normal processes such as the production the sticky secretions, which allow them to stick to teeth, and the production of acid to break down the enamel on teeth. Essentially, polyphenols block cell metabolism, which prevents normal action of the bacteria, lowering the possibility of dental caries (3). Because of this, there are many products like tea and chewing gum that use green tea extract to attract customers and to provide an alternative to gum with high levels of sugar that act as nutrients for bacteria like S. mutans.

Recent studies have revealed that the uncontrolled presence of S. mutans is linked to heart disease. Without routine dental hygiene, S. mutans is able to build up on teeth and cause plaque. This plaque can be broken off from the teeth during mastication and ingested into the body. From there, the plaque can enter the blood stream and cause blockages in arteries in the heart and also the hardening of arteries (6). Before this discovery, the effects of S. mutans were believed to be confined to tooth decay and diseases in the mouth. This discovery in 2005 showed this to be incorrect. The plaque found in arteries contained high levels of S. mutans and low levels of all other bacteria, showing that S. mutans was able to live on this plaque and continue to produce more in vital areas of the body, such as the heart (6).

References

1.) Adjic, D., and W. M. McShan. "Genome Sequence of Streptococcus Mutans UA159, a Cariogenic Dental Pathogen." Proceedings of the National Academy of Science 22 (2002).

2.) Bergey, D. H., and John G. Holt. "Bergey's Manual of Determinative Bacteriology." 9th ed. Baltimore: Williams & Wilkins, 1994. Print.

3.) Horiba N, Maekawa Y et al. A pilot study of Japanese green tea as a medicament: antibacterial and bactericidal effects. J Endod. 1991 Mar;17(3):122-4.

4.) Klein, P., and M. Scholler. "Recent Advances in the Development of a Streptococcus Mutans Vaccine." European Journal of Epidemiology 4.4 (1988): 419-25.

5.) Mukasa, Hidehiko, and Hutton D. Slade. "Structure and Immunological Specificity of the Streptococcus Mutans Group B Cell Wall Antigen." American Society for Microbiology 7.4 (1973): 578-85

6.) Nakano, K., H. Inaba, R. Nomura, et al. "Detection of Cariogenic Streptococcus Mutans in Extirpated Heart Valve and Atheromatous Plaque Specimens." Journal of Clinical Microbiology 44.9 (2006): 3313- 317.

7.) O'Leary, William M. "Practical Handbook of Microbiology." Boca Raton, FL: CRC, 1989. Print.

8.) Thomas, E.L., and Pera, K.A. "Oxygen metabolism of Streptococcus mutans: uptake of oxygen and release of superoxide and hydrogen peroxide." American Society for Microbiology 154.3 (1983): 1236-1244

Edited by student of Dr. Lynn M Bedard, DePauw University http://www.depauw.edu