Streptococcus Mutans: Causes, Effects and Transmission

Introduction

Streptococcus mutans is the bacteria responsible for dental cavities in humans. The full taxonomy, or classification of the organism, is Bacteria Firmicutes Bacilli Lactobacillales Streptococcaceae Streptococcus Mutans (1). From S. mutans’ scientific name one can understand quite a bit about the bacteria. The domain and kingdom are Bacteria, meaning S. mutans is a one celled organism that doesn’t have a distinct nucleus. The phylum Firmicutes tells us that the cell wall is strong, thick, and most likely Gram-positive. The class Bacilli explains the rod-shape of the bacteria. The order is Lactobacillales and the definition of Lactobacillales is “lactic acid bacteria”. Streptococcaceae family classifies S. mutans as Gram-positive, facultative anaerobe, usually nonmotile, and found in pairs, chains, or tetrads. From the genus of streptococcus, we know that the bacteria is non spore forming, in pairs or chains, and usually requires a complex culture medium to grow. Finally, the species Mutans specifies that the bacteria lives in our mouths and causes dental cavities. Cavities are permanent tooth decay that makes holes in teeth and are usually painful. They can lead to more serious health complications.

Morphology

The morphology of S. mutans, or form and structure of an organism, is why this bacteria can create cavities so well and why it is so hard to kill. S. mutans is 0.5 to 0.75 micrometers in diameter, Gram-positive cocci, strepto arrangement(1,2). To put the size of S. mutans into prospective, a micrometer is one millionth the size of a meter. Gram- positive cells turn purple from crystal violet in the Gram stain test. Gram-positive cells turn purple because the cell wall is composed of a thick layer of peptidoglycan, a polymer made from polysaccharide and peptide chains(1). The peptidoglycan holds onto the crystal violet and doesn’t let it get washed out. This component of the cell wall also prevents osmosis lysis. That means the cell will not burst from an imbalance of solvent concentration from inside the cell to the outside of the cell. Streptococci bacteria such as S. mutans are cocci, or a circular bacteria that sticks together in a line, or strepto arrangement. This single cell organism does not have a nucleus or organelles in its cytoplasm. The genetic material is kept in single strands that get duplicated during binary fission, which is how the cell reproduces because it does not produce spores. This bacteria has a capsule composed of polysaccharide and dextran glucose. S. mutans uses a protein on its surface to attach itself to a tooth, the bacteria then grows this dextran capsule that is a slime that binds the bacteria to the tooth enamel. In this slime is where the bacteria divides and produces colonies, this is a biofilm. S. mutans is a facultative anaerobe so the bacteria uses oxygen if it is present, but does not need oxygen to survive(2). This mesophilic bacteria grows best at 18 to 40 degrees Celsius (64 to 104 degrees Fahrenheit)(1). All of S. mutans morphology makes it completely adapted to living in such an extreme place as a mouth.

Biofilm

S. mutans is an animal parasite, especially in animals with a high carbohydrate diet. Because this bacteria is a parasite, it needs a host to survive and the host suffers from the bacteria. S. mutans is the main reason for dental cavities and is found mostly on the surface of teeth. It is found in higher concentration in the natural crevices and fissures of teeth. On these surfaces S. mutans creates plaque. Plaque is a biofilm. Biofilm is microorganisms sticking to a surface and to each other in an extracellular matrix that is usually self-produced. Plaque is formed in three steps. First the pellicle, or film, is formed. The pellicle is the dextran polymer capsule on the bacteria. This also becomes the extracellular matrix of the biofilm. Second is the cell to surface attachment of S. mutans to the tooth(1). Last is later S. mutans attaching to the first S. mutans that landed on the tooth. This plaque biofilm is 300-500 cells(1). Plaque formation begins immediately after the tooth surface is cleaned and takes four to seven days for the plaque to become fully mature. After only one to two days of uninterrupted formation, the plaque is visible. Plaque can calcify and become hard, forming calculus. Plaque will continue to grow over calculus(3).

Metabolism

S. mutans have a fairly simple metabolism. A metabolism is the chemical processes that occur in an organism to maintain life. S. mutans cleave, or cut, sucrose from the host’s diet into glucose and fructose(1). They eat these food particles with channels in their cell wall that help molecules cross the cell wall and get into the cell(4). If there are no food particles the bacteria leaks an enzyme that attacks and breaks down certain tissues in its environment. The fructose that came from the sucrose is fermented and used as an energy source for the bacteria to grow. The glucose is polymerized into the dextran polymer that is the extracellular matrix that cements the S. mutans to tooth enamel(1). The dextran slime can later be depolymerized back into glucose. This glucose would be used as a carbon source that results in the production of lactic acid. The lactic acid in the plaque decalcifies the enamel and leads to cavities and infections of a tooth.

Diseases

Cavities caused by S. mutans cause many unpleasant symptoms and may cause more health issues. When a cavity is just beginning you may not have any symptoms, this makes cavities hard to catch unless you visit the dentist regularly. Once the cavity gets larger it can cause a toothache, tooth sensitivity to something as simple as the air we breathe, pain when eating or drinking anything sugary, pain brought on by hot or cold substances, pain while chewing or biting down, and a bitter taste in your mouth. Cavities will create visible holes, discoloration on teeth, and bad breath, which can lead to low self-esteem and poor social interactions. If cavities get deep enough to get into the pulp chamber of the tooth, it can cause an abscessed, or infected, tooth. The cavity causes inflammation in the center of the tooth and an infection forms. The infection will create a puss pocket, this is the abscess. Abscesses can spread to the gum and jaw bone, causing pain and inflammation. Sometimes the pain caused by an abscessed tooth is so extreme it can’t be relieved by pain medication. If the abscess spreads quickly it can cause fever and swelling in the face. If an abscess pops it may cause flu- like symptoms. These abscesses that are caused by the cavities created by S. mutans can lead to another mouth disease, periodontal disease. Periodontal disease is divided into two categories: gingivitis and periodontitis(5). Gingivitis is less severe and more common, it is the inflammation of gum tissue. Periodontitis is an inflammatory response due to plaque that causes the gum to come loose from the tooth and recede and causes loss of bone in the jaw. In extreme cases, the gum recedes enough to expose the entire root of the tooth. The overall oral health of an individual is closely related to health throughout the body. Heart disease, stroke, endocarditis, premature birth and low birth weight, diabetes, and osteoporosis are all closely linked to periodontal disease and other mouth infections. S. mutans can cause some serious health issues if proper oral health is not maintained. The surgeon general has called tooth decay the “silent epidemic”.

Transmittion

S. mutans take up 30 to 60 percent of an adult’s normal oral flora(4). This means out of all the normal microorganisms that live in a mouth S. mutans is one of the most common. Adults have a higher concentration of this bacteria in their mouths, but children are more vulnerable to it(1). The most common transfer of S. mutans is from a caregiver to a child. It can be passed vertically, or from a mother to a baby immediately before and after birth. So, if a mother has a lot of S. mutans bacteria there is a good chance the child will inherit that trait. The bacteria can also be passed horizontally, or from one person to another. Saliva will pass S. mutans from one person to another. If a caregiver shares eating utensils with a child, they are giving that child the S. mutans bacteria. If the child doesn’t have teeth the bacteria will colonize in furrows of the tongue(1). Cavities are the most common childhood disease. A child is five times more likely to suffer from cavities than asthma.

Prevention and Treatment

Cavities are the reason for half of all dental visits and two billion dollars are spent a year in treatment(1). S. mutans are extremely hard to treat with medicine because biofilm cells are 1,000 times more tolerant to antibiotics(4). There is no cure for S. mutans because of its virulence factors. It contains water insoluble glycan, has an acid tolerance, and produces lactic acid. Although we can’t get rid of this bacteria, we can prevent and treat its diseases. Brushing at least twice a day, especially after meals, and flossing at least once a day can help prevent cavities causes by S. mutans. If there isn’t any food particles for the bacteria to break down, it can’t form lactic acid to break down the enamel. Fluoride treatments also help prevent cavities by strengthening the tooth enamel. Enamel is the human body’s most mineralized substance. Fluoride can also reverse some decalcification caused by the lactic acid through a process called remineralization. Visiting the dentist every six months for a cleaning is recommended. Dentists and dental hygienists will help prevent the damage done by S. mutans and will catch cavities in early stages. Dentists can also apply sealants to the crevices on the chewing side of molars. A sealant is a thin plastic-like coating that will prevent plaque from building up on the tooth itself. Everyone has the S. mutans bacteria and the only thing anyone can do to prevent cavities is to lessen the impact of the acid fermentation caused by this bacteria. Once cavities have formed a dentist will give fillings. Dentist’s drill a small area around the cavity to fit either an amalgam or a composite filling inside of the hole or divot created by the lactic acid. Amalgam fillings are the silver-looking fillings many people have. They are durable, strong, last 10-15 years, and are less expensive than the composite fillings. The negatives of amalgam fillings are they discolor the tooth, cause cracks and fractures, allergic reactions, and destroy tooth structure. Composite fillings look better because they are made to look the same color as a tooth. They are also chemically bonded for better support and less tooth needs to be removed prior to putting the filling in. The negatives of the composite filling are they need to be replaced about every five years and they are double the cost of amalgam fillings. If a cavity is too bad the dentist may need to perform a root canal and remove the nerves from the tooth. That tooth will then be dead, but it will not hurt anymore. In some cases a dentist might just need to pull a tooth out.

Future

A University of Florida oral biology professor, Jeffrey Hillman has found a way to tweak the S. mutans bacteria in a way that the bacteria will stop converting sugar into lactic acid. Without lactic acid there are no cavities. S. mutans and humans used to live together in harmony until relatively recently when our diets contained more refined sugar. Hillman’s vision is to have patients swish the dominant modified bacteria in their mouths for a few minutes, then chew gum to activate it. At that point that person would be cavity free for life. Hillman calls this “replacement therapy”(6).

Conclusion

S. mutans can very easily live in our mouths because of factors such as its peptidoglycan cell wall that makes it hard to penetrate and polysaccharide and dextran glucose capsule that adheres the bacteria to teeth and forms its matrix. That same dextran slime creates lactic acid that breaks down the calcification on our enamel, creating cavities. Cavities can lead to more serious health issues. There is no guarantee to preventing diseases caused by S. mutans. Brushing, flossing, and dental visits are the best thing one can do to prevent the diseases. Maybe one day Hillman’s discovery will be utilized so humans and Streptococcus mutans can live in harmony again.

References

1. Streptococcus mutans. MicrobeWiki. The student editied microbiology resource. Microbewiki.kenyon.edu/index.php/Streptococcus_mutans Edited 2014
2. Heather Payne. Streptococcus mutans. Missouri S&T. web.mst.edu/~microbio/BIO221_2005/S_mutans published 2005
3. Time and Rate of Plaque Formation. University of Illinois at Chicago. www.wic.edu/classes/peri/peri311/lec8sm/dentalplaque3.htm
4. Amber Allmann. Streptococcuss mutans. University of Wisconsin La Crosse. Bioweb,awlax.edu/bio203/s2007/allmann_ambe/ Published 2007
5. Walter J. loesche. Microbiology of Dental Decay and Periodental. Medical Microbiology. www.ncbi.nlm.nh.gov/books/NBK8259 Published 1996
6. Explore. Tackling tooth decay. Researched at The University of Florida. www.research.wfl.edu/publications/explore/V09n2/feature_03.html Published summer of 2004