What are the bacteria in the mouth?

There is a large number and diversity of bacteria in the mouth. Most of these bacteria are fought off by enzymes in saliva, but there are also many that survive and lodge in different areas, sometimes causing health problems.

Bacteria in the mouth are very numerous. In fact, it is estimated that there are around 100 million bacteria for every millimeter of saliva. These correspond to more than 600 species of bacteria. In reality, the oral cavity has all the conditions for countless microorganisms to take refuge there.

Despite everything, many of the bacteria in the mouth have no future in the human body. A good part of them are attacked by the enzymes in the saliva, while another part goes to the digestive system, where they are destroyed in a short time.

That said, it should also be noted that another group of bacteria in the mouth does manage to survive and ends up staying in the oral cavity. When this happens, they can lead to problems such as cavities or other diseases. The way to combat them is with good oral hygiene.

Bacteria in the mouth

The mouth is made up of many surfaces, each of which is covered by a large number of bacteria. Some of the bacteria in the mouth play a role in the development of diseases such as tooth decay and periodontitis. Both are risk factors for developing other more serious diseases, such as diabetes mellitus and cardiovascular diseases.

The composition and concentration of bacteria in the mouth depends on several factors:

  • Nutrient availability
  • Temperature
  • Oxygen concentration
  • Anatomical features
  • Exposure to immune factors
  • Bacteria in the mouth, along with other microorganisms, are known as the oral microbiota. That population is not fixed, but is continually changing, even due to factors as simple as yawning, kissing, or eating certain foods.
  • In general, aerobic and anaerobic bacteria predominate inside the mouth, both gram-positive and gram-negative. Among these, the Lactobacillus, Actinobacillus, Staphylococcus or Streptococcus genera stand out . Let’s look at this in more detail.

Saliva and bacteria

In saliva, facultative anaerobic gram-positive cocci predominate, representing around 44% of the bacterial population; it is followed by strict anaerobic gram-negative cocci, which account for about 15%. Gram-positive facultative anaerobic bacilli have a similar percentage.

Factors such as the loss of teeth, and diseases such as gingivitis, alveolitis or periodontitis, can produce changes in the composition of the saliva microbiota. Tobacco use and poor hygiene also play a role.

Buccal mucosa

The following types of bacteria predominate in the oral mucosa: Firmicutes mainly of the Streptococcus and Veillonellas genera; proteobacteria especially Neisseria; bacteroides-Prevotella and actinobacteria, micrococcineae.

Good hygiene  of the oral mucosa prevents colonization by Treponema denticola and Fusobacterium Nucleatum. According to some studies, bacteria on the oral mucosa could be involved in some types of cancer.

Bacteria in teeth

If the teeth do not have cavities, the following bacteria are usually found there: Campylobacter, Granulicatella, Kingella, Leptotrichia, and Streptococcus- especially Streptococcus sanguinis. Likewise, Haemophilus parainfluenza, Gemella haemolysans, Slackia exigua, and Rothia species are present, especially in adults.

The teeth are surfaces that facilitate the formation of biofilms. Such biofilms change based on different factors. Some bacteria such as Streptococcus mutans, Actinomyces, and Lactobacillus affect tooth decay and periodontitis.

Gums and bacteria in the mouth

A biofilm can also form on the gums, which can cause diseases such as gingivitis. If the gums are healthy, microorganisms such as Proteobacteria predominate, in particular the gammaproteobacteriae of the genus Acinetobacter, Haemophilus and Moraxella. When there are health problems, there are also Streptococcus, Granulicatella and Gemella.

In the superficial part of the biofilm of the gums there is Treponema denticola together with Porphyromona gingivalis and Tannerella forsythia. Likewise, there may be viruses and, sometimes, microorganisms such as fungi. Oral diseases modify bacterial communities.


The biofilm that forms on the tongue is also dynamic and harbors many of the bacteria in the mouth. Approximately 45% are facultative anaerobic gram-positive cocci, especially Streptococcus salivarius, followed by Streptococcus mitis, milleri group streptococci, and Streptococcus mucilaginosus.

Strict anaerobic gram-negative cocci and facultative anaerobic gram-positive bacilli are also found. To a lesser extent, various species of the Lactobacillus, Neisseria, Fusobacterium and Haemophilus genera can be detected. Fusobacterium nucleatum, Porphyromona gingivalis, and Tannerella forsythi have been found on the back of the tongue of people with halitosis.

Prevent pathogenic bacteria in the mouth

Oral hygiene is the key to preventing pathogenic microorganisms that affect our oral cavity. In the same way, frequent visits to the dentist make it possible to identify risk factors and incipient pathologies that can be stopped before definitive damage. If you have doubts, or it has been a long time since you had a mouth check up, go to a specialist and consult him.

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