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Definition of Anaerobic and Aerobic Bacteria

Bacteria are extremely small, single-celled microorganisms that can exist either freely or as a parasite. They are invisible to the naked eye and can only be seen under a microscope. Broadly, bacteria are classified into two main groups, based on oxygen requirements: aerobic and anaerobic bacteria.

  1. Aerobic and Anaerobic Bacteria

    • Aerobic bacteria, also called aerobes, can live and survive only in an oxygenated environment. They use oxygen for complete metabolic breakdown of food molecules. Anaerobic bacteria or anaerobes, by contrast, can grow even in the absence of oxygen. Such bacteria most commonly infect deep tissues, internal organs, and deep lacerations.

    Types

    • There are many particular types of aerobic and anaerobic bacteria, such as obligate aerobes (e.g., Nocardia), obligate anaerobes (e.g., Bacteroides), and facultative aerobes (e.g., Salmonella typhimurium). Obligate aerobes require oxygen for the oxidation of substrates (such as sugar and fat) in order to derive energy whereas obligate anaerobes do not require oxygen for the breakdown of substrates. Furthermore, they get killed in the presence of oxygen. For facultative anaerobes, oxygen is not the limiting factor because they can survive both in the presence and absence of oxygen.

    Identification

    • The best method to identify aerobic and anaerobic bacteria is by growing them in a liquid culture. The obligate aerobic bacteria will start collecting at the top of the test tube so that it can absorb sufficient amount of oxygen whereas the obligate anaerobic bacteria will settle at the bottom to avoid oxygen. Most facultative bacteria gather at the top of the test tube, but since the absence of oxygen also does not harm them, they can spread evenly along the culture. Another bacteria type, microaerophiles, such as Borrelia burgdorferi, require oxygen at a lower concentration and therefore collect at the upper part of the test tube. On the other hand, aerotolerant bacteria like Haemophilus influenzae remain unaffected by oxygen and can be present throughout a test tube.

    Examples

    • Some examples of aerobic bacteria include Pseudomonas aeruginosa, Bacillus, and Mycobacterium tuberculosis. Some examples of anaerobic bacteria include E. coli, Bacteroides, Staphylococcus aureus, and Clostridium botulinum.

    Human Occurrence

    • Aerobic bacteria primarily cause infections of lungs and kidneys. There are two types of aerobic bacteria--those that may cause illness and those that do not pose any threat to humans or may at times be helpful. Anaerobic bacteria are most commonly found in the gastrointestinal tract, mouth, vagina, and skin surface. Marked symptoms of infections (including STDs such as syphilis, gonorrhea, and chlamydia) caused by anaerobic bacteria include the formation of abscesses, foul-smelling pus, and tissue damage. These bacteria can cause diseases such as botulism, tetanus, dental infections, and gangrene.

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