Oral Bacteria – The Good, The Bad and The Harmless


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Dr Baani Adhvaryu
Baani has done BDS. She enjoys reading in her free time. Her weak spots are quirky stationery and witty puns. She is currently interning as a dentist and plans to pursue a career in the research-oriented domain of public health.

Our mouth is more than just teeth, tongue, palate and saliva. It is home to thousands of micro-organisms that we can’t see, touch or feel. Some of them are Streptococcus Mutans, Porphyromonas gingivalis, Actinomyces, and Lactobacilli.

Though each person has only a few strains of bacteria, researchers know of at least about 700 different strains to exist. Which bacteria flourish in your mouth and which don’t?


This depends on your oral hygiene, your overall systemic health, and even your genetic build up.

What do we know about oral bacteria?

Most humans have between 35 to 70 different bacterial strains in their oral cavity. These bacteria are everywhere. They form a layer on the tongue, they adhere to enamel, and they also stick to the mucous lining of the mouth.

Out of all the bacteria in the mouth, there are some microbes which help in digestion and are good for our oral health. These are called probiotic bacteria.

Sometimes we even artificially ingest these for improving our health. Most of the bacterial strains in the mouth are harmless. It is a specific few strains which cause oral diseases in the mouth.

There are no bacteria in a newborn baby’s mouth. In a few hours of their birth, the first bacterial strain streptococcus salivarius appears.

Over time other species of streptococcus colonize the oral cavity. (1) The population of the bacteria changes with age. The bacteria that cause oral diseases in children may not be the same as the ones that cause oral problems in adults.

In a laboratory, these microbes multiply every twenty minutes on an average. But the conditions in the mouth are not ideal. Activities like brushing and flossing destroy these bacteria.

Saliva also has anti-bacterial properties. Hence the rate of multiplication is lesser in the mouth.

Broadly, bacteria are called aerobes or anaerobes, based on their need for oxygen. Anaerobic bacteria survive even in the absence of oxygen, and they are involved in many stages of oral pathologies.

The factors which control the population of oral bacteria are diet, brushing habits, the quantity of saliva, habits, and our dental habits.

When you get any dental work done, or take medicines to treat a dental problem, you are essentially destroying the bacteria that are causing the problem.

Oral bacteria have to be kept in check, because if these flourish they can cause more severe problems like respiratory infections and gastric disorders.

Some common bacteria in the mouth

In most people, the same few bacterial strains cause decay and gingival problems.

Streptococcus Mutans

Streptococcus Mutans is the most common bacteria in the mouth. It is present by itself in the oral cavity and is harmless in that state.

But when you eat sugar-containing food, the organism comes in contact with that and releases acids. These acids attack your enamel, and the process of tooth decay begins. (2)

S.Mutans, which is a round anaerobe, has a dominant presence in the oral cavity. It has developed resistance to agents that destroy it, and over time the strains of this bacteria multiply in our mouths. This bacteria is also linked to heart disease.

Porphyromonas gingivalis

Porphyromonas gingivalis is a rod-shaped anaerobic bacteria, which is absent from our mouths in healthy conditions. But, it is very likely that every person’s mouth contains p.gingivilis in a small quantity.

This is because we can never wholly be disease free. Porphyromonas gingivalis is responsible for gingival and periodontal disease in our mouths.

It causes a shift in the microbial distribution during the onset of periodontal disease and is considered the primary micro-organism responsible for our deteriorating periodontal health. (3)

Apart from being a disease-causing bacteria itself, p.gingivilis also increases the virulence of other bacteria. For this reason, this anaerobe is considered to be at the forefront of a diseased mouth.


Actinomyces are bacteria which are typically present in the gums. They can survive without oxygen, and they are the most common cause of infection during a dental procedure.

When you develop a dental abscess, this is a bacteria that is sure to colonize the abscess. A species of actinomyces also thrives during periodontal disease. (4)

Other than the mouth, it is also found in the gastric tract and can even cause a lung abscess.


Lactobacilli are rod-shaped bacteria found in different parts of the body. In the mouth, lactobacilli contribute to caries progression and not caries initiation.

Their primary role consists of converting sugar to lactic acid. Lactic acid erodes the tooth enamel. Lactobacilli are also used as indicators of decay, in caries activity tests. (5)

Conversely, some species of lactobacilli are also probiotics, which means they help in caries prevention.


How you can drive the harmful bacteria away?

Bacteria thrive in the mouth if they get a favorable environment. However, there are simple methods by which you can prevent these microscopic creatures from wreaking havoc in your oral cavity.

  • Oral hygiene – There is nothing that will substitute a clean mouth. The only way to do this is to brush twice daily, floss regularly and use other supplementary cleaning aids. Use the right brushing technique, and do not forget to clean your teeth.
  • Reduce the intake of sugar, candies, sweets and acidic beverages. These are the foods which bacteria thrive on. When they come in contact with such food, they metabolize the sugar to form harmful acids which cause caries.
  • Keep your oral cavity hydrated. If the mouth is dry, bacteria flourish. This is because saliva has critical antibacterial properties which fight these microbes. The defensive function of saliva is crucial to keep the bacteria in check.
  • Do not delay dental treatment. If you have a painful tooth or bleeding gums, see your dentist and seek treatment immediately. By letting a pathology stay in the mouth, you are allowing the harmful bacteria to multiply.
  • Quit habits like smoking. These habits inhibit the defense cells of the mouth, making you more prone to oral diseases.
  • Even if you are experiencing no pain or discomfort, visit your dentist for a check-up every six months. It is good to get your teeth cleaned, and have them checked for any anticipated dental problems.

That’s it on oral bacteria

While you cannot drive away every single bacterium strain in your mouth, you can surely give a tough fight to the microbes by making good oral hygiene a routine.

Don’t let the bacteria multiply to the extent that they become more powerful than your defense system, visit your dentist before that happens!


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