Types of anaerobic bacteria with examples

The anaerobic bacteria, also called anaerobic bacteria are bacteria that do not need oxygen to live. Some anaerobic bacteria die in the presence of oxygen, known as strict anaerobes, while others can tolerate it and others even use it if it is available in their environment.

In the human body, they can be found under normal conditions as part of the intestinal flora. They are also very common in the environment and can be found in many places, including soil, water, food, and in the body of other animals.

Some anaerobic bacteria are beneficial to humans, while others can cause diseases such as appendicitis, diverticulitis, or gingivitis.

Types of anaerobic bacteriatypes of anerobic bacteria

Anaerobic bacteria list can be classified into three Types based on their ability to live in the presence of oxygen and their ability to use it:

  1. Anaerobic bacteria bound s
  2. Anaerobic aerotolerant bacteria
  3. Facultative anaerobic bacteria

1.- Anaerobes required

Anaerobic obligate bacteria need an oxygen-free environment to live. They cannot grow in places with oxygen since it can be harmful, even kill them.

They are also known as strict anaerobic bacteria. An example of forced anaerobic is Porphyromonas gingivalis . This bacteria is frequently found in the mouth and is believed to be related to some forms of rheumatoid arthritis.

2.- Anaerobic aerotolerant bacteria

Although aerotolerant anaerobic bacteria never use oxygen in their biological processes, they can live in environments where oxygen exists.

A common example of wind tolerance is Pronibacterium acnespio. This bacteria normally exists on the skin of any person and is a factor that contributes to the development of acne.

In rare cases, it can enter the body and cause endocarditis (inflammation of the endocardium, the lining tissue of the heart chambers).

3.- Optional anaerobic bacteria

The facultative anaerobes can use oxygen to live if any (aerobic respiration) and if there is no oxygen fermentation processes used to obtain the energy required for their development (fermentation is a process that does not use oxygen).

Some species of the genus Staphylococcus are facultative anaerobes; one of the species of this genus that is best known is Staphylococcus aureus, a bacterium that produces various types of infections in humans, for example, skin infections, such as acne, boils or impetigo, and other more serious ones such as endocarditis, meningitis, pneumonia or septic shock.

Another facultative anaerobic bacterium well known to all is Escherichia coli. E. coli is found in the intestinal flora of many healthy mammals, which it assists in the absorption of nutrients in the intestine.

Metabolism: fermentation and anaerobic respiration

The energy metabolism of anaerobic bacteria can follow several pathways to synthesize ATP. Some perform anaerobic respiration and others follow a fermentative metabolism.

The facultative anaerobic bacteria are all fermentors. Strict anaerobes can be fermenting or anaerobic respiration.

The aero-tolerant ones perform aerobic respiration if there is oxygen, and if there is no oxygen they perform fermentation or anaerobic respiration, according to each specific species.


The fermentation is the most used type of metabolism by anaerobic bacteria for energy and ATP. There are many types of fermentation depending on the final product it produces, but in no case does an electron transport chain intervene as occurs in respiration.

Among the most common fermentation, we have:

    • Lactic fermentation: the final product is lactic acid.
    • Alcoholic fermentation: the final product is organic alcohol, for example, ethanolic fermentation produces ethanol.

Anaerobic breathing

The anaerobic respiration is a metabolic process to synthesize ATP, and the like aerobic respiration, using an electron transport chain, but instead of oxygen as the terminal electron acceptor chain, another molecule appears. In both cases, it is much more efficient than fermentation.

The last electron acceptor in anaerobic respiration is usually an inorganic molecule, such as (SO 2- 4 ), nitrates (NO – 3 ), carbon dioxide (CO 2 ), or ferric ion (Fe 3+ ). In some cases, it can be an organic molecule, such as fumarate or chlorobenzoate.

Beneficial anaerobic bacteria

Among anaerobic bacteria, we can find many examples of bacteria that provide some benefit to humans and many other examples that cause problems. There are even some that can be both beneficial and harmful depending on the quantity or the specific situation.

The Bacteroides genus is an example of anaerobic bacteria that are both beneficial and harmful. In the digestive tract, various species of this genus help to carry out digestion, but if they invade other parts of the body they can cause pneumonia, meningitis and other diseases.

We can also find anaerobic bacteria beneficial to humans, although not always for their bodies. For example, some Lactobacillus species are used in cheese making.

Some types of Clostridium are used in soil regeneration by converting soil-polluting substances into carbon dioxide and other non-toxic substances for cultivation (a process known as bioremediation ), but some Clostridium species cause serious diseases.

Anaerobic bacteria infections

Many anaerobic bacteria are the cause of infection in various organs and tissues and are usually more difficult to treat than aerobic infections since by being able to live without oxygen, anaerobic bacteria can infect places where other types of microorganisms do not reach.

They can infect injuries and wounds of the skin, mouth, digestive tract, and respiratory tract, including the bronchi and lungs, but they can also infect areas in the complete absence of gaseous oxygen.

For example, obligate anaerobic bacteria can cause abdominal peritonitis, or go into the blood and cause endocarditismeningitis, and other serious infectious diseases.

Many species of anaerobic bacteria can be found in the body of a healthy person. For example, several Actinomyces species normally live in the oral cavity and other areas of the upper respiratory tract, and may also appear in the gastrointestinal tract.

Other species only appear in specific areas of the body, such as some bacteria that we only find in the colon, for example, the genus Bacteroides, very common in human feces and that can cause tissue destruction if they infect wounds of the intestinal mucosa.

The most common symptoms of anaerobic bacteria infection are pain and fever, along with inflammation and suppuration. For example, a periodontal infection often causes pain, inflammation, and bleeding with oozing gums and a foul odor.

Throat infections are often accompanied by pain, swelling, choking sensation, fever, and bad breath. Lung infection cases are characterized by shortness of breath, cough, chest pain, and fever.

As in any case of infection, there is an increased risk in people with compromised immune systems, either due to illness or some treatment. People who have had surgery or have open wounds are also at higher risk.

Diabetes mellitus, impaired blood circulation, and cancer are also risk factors for bacterial infections.

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