AEROBIC BACTERIA: CHARACTERISTICS, EXAMPLES, CULTURES, DISEASES - BIOLOGY - 2025

The aerobic bacteria are a broad group of bacteria that are characterized need oxygen for their metabolic processes. These bacteria use oxygen to break down organic compounds to simpler compounds through a process known as cellular respiration.

Many specialists argue that the appearance of this type of bacteria is a direct consequence of the photosynthesis process. Due to this, atmospheric oxygen levels increased and were initially toxic to many living beings. Because of this, many organisms had to adapt and start using oxygen.

Mycobacterium tuberculosis, aerobic bacteria. Source: Photo Credit: Janice CarrContent Providers (s): CDC / Dr. Ray Butler; Janice Carr

There are many species that are included within the group of aerobic bacteria. The most representative are those of the Bacillus, Mycobacterium and Nocardia genera. Similarly, many of these bacteria are known human pathogens, even causing pathologies that can cause death.

characteristics

The main characteristic of aerobic bacteria is that in order to develop they necessarily require an environment in which there is ample oxygen availability, since within their metabolism they carry out the process of cellular respiration.

In this process they use oxygen to break down molecules of organic compounds, such as glucose, to simpler compounds such as carbon dioxide and water, with the consequent obtaining of energy in the form of ATP.

Likewise, most of the species that make up this group do not have the ability to synthesize the catalase enzyme, so they cannot split the hydrogen peroxide molecule into water and oxygen.

Types of aerobic bacteria

In general, it is understood that aerobic bacteria are those that require the presence of oxygen in order to develop and grow. However, the need for this chemical element in bacteria in this group is not the same for all. In this sense, there are several types of aerobic bacteria: obligate aerobic, facultative anaerobic and microaerophilic.

Obligate aerobic bacteria

They are bacteria that necessarily require oxygen to develop. They require this element to carry out the process of cellular respiration.

Facultative anaerobic bacteria

These are bacteria that from the evolutionary point of view have a certain advantage, since they can survive both in environments where there is a presence of oxygen, and in those environments where there is an absence of it.

This is due to the fact that within their cellular machinery, they have the necessary elements to carry out anaerobic processes through which they can obtain energy. In such a way that in the absence of oxygen, these bacteria do not die, but carry out other metabolic processes.

Microaerophilic bacteria

This is a very particular type of bacteria. They use oxygen as a primary element to carry out the process of cellular respiration. However, atmospheric concentrations of this gas (Approximately 21%) are toxic to these bacteria.

Aerobic bacteria species

Bacteria of the genus

The genus Bacillus is made up of a great variety of species, which are characterized by having a rod shape and being gram positive. One of the most outstanding characteristics of these bacteria is that when environmental conditions become hostile, they generate spores in their cells. These are very resistant and are intended to ensure that the bacteria can survive in harmful environmental conditions.

Within this genus there are bacteria that are strictly aerobic, while there are others that are considered facultative aerobic. Among the species of bacteria of the genus Bacillus we can mention: Bacillus anthracis, Bacillus cereus, Bacillus subtilis and Bacillus thuringiensis, among others.

Bacillus

It is a well-known and studied bacterium in the world of microbiology, since due to its potential and evident pathogenicity, it has been used as a biological weapon. Its spores are very toxic and easily penetrate the human body, through the respiratory tract by inhalation, by ingesting contaminated food or by contact with an open wound.

Already in the body it causes an infection that, in a generic way, is known by the name of anthrax, which can be cutaneous, pulmonary or gastrointestinal.

Bacillus cereus

It is a facultative aerobic bacterium that is well known for producing toxins. These toxins can cause various pathologies in humans, such as emetic syndrome and diarrheal syndrome, both at the gastrointestinal level. Likewise, it can affect other organs, such as the eyes, in which it can cause keratitis and endophthalmitis.

Bacillus subtilis

It is perhaps the most studied species of the genus Bacillus. So much so that it is considered the "type species". Like other Bacillus species, it produces spores, specifically endospores that are found in the center of the bacterial cell.

It is a harmless bacterium for humans, except for some very isolated cases of poisoning from contaminated food. In addition to this, it carries a wide range of benefits, such as the synthesis of antifungal and antibiotic substances, as well as applications in the industrial area.

Nocardia

It is a genus of gram positive bacteria that are shaped like bacilli. Among its most outstanding characteristics, it can be mentioned that they have ramifications, many of which are at right angles.

Likewise, these bacteria are well-known human pathogens. Two of its species in particular, Nocardia asteroides and Nocardia brasiliensis, have been sufficiently studied as causing pulmonary nocardiosis and actinomycotic mycetoma respectively.

Lactobacillus

They are gram-positive bacteria that are characterized by being facultative aerobic, having the shape of a bacillus and not producing spores. These bacteria are generally considered innocuous and harmless to humans.

On the contrary, they are famous for the benefits they provide, among which we can highlight: they contribute to the preservation of food, help control some diseases -such as colon cancer-, and are part of the synthesis of certain compounds, like the B vitamins.

Staphylococcus

These are coconut-shaped (round) bacteria that tend to form clumps of cells that look like a bunch of grapes. Bacteria of this genus are considered facultative aerobic, which means that they can develop both in the presence and in the absence of oxygen.

Many of the species in this genus are known human pathogens. Among these, the most virulent is Staphylococcus aureus, which produces certain toxins: hemolysin, enterotoxin, toxic shock syndrome toxin, and exfoliative toxin. These toxins cause diseases such as diarrhea, pseudomembranous colitis and scalded skin syndrome.

Difference between aerobic and anaerobic bacteria

Anaerobic bacteria appeared on the planet long before aerobic bacteria. This is because in the first eras of terrestrial life, oxygen was not a significant part of the atmosphere, so the living beings that existed then did not use it for their metabolic processes.

Later, as life evolved on the planet and the levels of atmospheric gases stabilized, aerobic organisms appeared, which began to use oxygen as the main element in energy production processes.

Now, the main difference between both types of bacteria is that aerobic bacteria require the element oxygen to carry out various cellular processes, the most characteristic being cellular respiration. Through this process they obtain a large amount of energy.

Anaerobic bacteria, on the other hand, do not use oxygen for any process. Even for some of these bacteria, oxygen is highly toxic. Due to this, they carry out other processes to obtain the energy that the cell needs.

Among these processes is fermentation, through which the degradation of certain compounds, such as carbohydrates, to obtain other organic compounds, such as lactic acid.

Another difference that can be mentioned between these two types of bacteria is the habitat in which they can be found. Anaerobic bacteria are usually found in places where there is little oxygen, such as in the tartar that covers the teeth, while aerobic bacteria thrive in habitats where there is enough oxygen, such as soil.

Aerobic bacteria culture

When a culture of aerobic bacteria is going to be carried out in the laboratory, the first thing to bear in mind is that these types of bacteria require an adequate amount of oxygen. In this sense, the same atmospheric conditions are known to be ideal. However, there are some bacteria that need extra aeration.

In these cases, what can be done is to vigorously shake the flask or bubble sterilized air through the medium. In the event that the cultivation is quite extensive, what is recommended is that the exposure of the medium to the atmosphere is increased. This is accomplished by layering the medium that is shallow.

Staphylococcus aureus culture. Source: Microrao

Now, with respect to the composition of the culture medium to be used for aerobic bacteria, this will depend on the bacterial species that is being cultivated. For example, for growing Staphylococcus aureus, the most commonly used culture media are 5% blood agar, trypticase soy agar, and BHI Brain Heart Infusion Broth. Bacillus bacteria are also successfully cultured in the aforementioned culture media.

It is important to note that BHI Brain Heart Infusion Broth is worldwide recommended for the cultivation of aerobic bacteria. Its composition includes a calf brain infusion and a bovine heart infusion, as well as peptone, sodium chloride and glucose, among other components.

Methods for plate counting

The plate count is a standard procedure that is carried out in laboratories in order to reach an approximate number of bacteria that make up a specific culture.

This technique is based on the count of so-called colony-forming units and allows obtaining an approximate number of bacteria. It is important to emphasize that this procedure must be carried out with the thoroughness and rigor that is required, since any error, no matter how small, can greatly affect the results.

There are several techniques that can be applied to perform the plate count. Two of them will be explained here.

Plate pouring technique

The first thing to do is prepare the ideal culture medium for the type of bacteria you want to grow. Later, in a clear and clean area, the Petri dishes in which the culture will be placed are placed.

In each Petri dish you should add 1mL of the corresponding dilution, as well as about 20mL of the culture medium that is melted. After this, movements with the Petri dish should be carried out as follows: 6 from right to left, 6 clockwise, 6 counter-clockwise, and 6 from back to front. Finally the medium is expected to solidify.

The Petri dishes are incubated in suitable temperature conditions (37 ° C) for 24-48 hours. Once this time has elapsed, the number of colonies that developed should be counted.

Surface spreading technique on the plate

To perform the count using this technique, the Petri dishes with the culture medium should be placed on the table in an orderly manner to avoid errors. Next, 1mL of each dilution is inoculated into each capsule.

Likewise, with the help of a glass rod, the inoculum should be spread homogeneously over the entire surface of the culture medium. This must be done through twisting movements.

Once the inoculum has been absorbed by the culture medium, the capsules are incubated for the time required according to the cultured microorganism. Finally, all colonies that have developed on the selected plates must be counted.

Diseases caused

As mentioned previously, some of the genera that make up the group of aerobic bacteria are known to cause disease in humans. Some of these diseases with their respective symptoms and treatments are listed below.

Nocardiosis

Nocardiosis is a disease that can present acutely or chronically. According to the clinical cases studied, most of the time they present with the symptoms of pneumonia. However, at times, rather than infecting the respiratory tract, it can affect the skin directly, causing characteristic lesions.

The symptoms seen in pulmonary nocardiosis are:

• High fever
• Chromic cough that is not relieved by anything
• Difficulty breathing
• General discomfort

On the other hand, when bacteria of the genus Nocardia invade the skin, what is known as actinomycetoma can develop. This is a chronic, granulomatous type of infection that is very rare and usually occurs in people who have a depressed immune system. Its symptoms include:

• Fever
• Nodular lesion that presents a central pustule through which bloody material may have drained.
• Cutaneous or subcutaneous abscess.
• General malaise

Anthrax

This is the name given to infections caused by the Basillus anthracis bacteria. It is caused by direct human contact with the spores of said bacteria. Anthrax can affect the lungs and skin. The pulmonary is the most dangerous, with a mortality rate greater than 90%.

A few years ago this bacterium became famous because envelopes containing spores were being sent, which greatly affected those who received them, causing death.

At first, the symptoms of anthrax in the lungs resemble those of a cold, however, as time passes, they evolve to a more compromised clinical picture:

• Persistent fever
• Difficulty breathing
• Increased heart rate.

Eventually the patient worsens and septic shock occurs, after which the death of the patient occurs in most cases.

With regard to cutaneous anthrax, the first sign is a lesion similar to a mosquito bite, which becomes chronic and evolves into a necrotic eschar.

There is also a rise in body temperature and general malaise. This clinical picture often resolves favorably, leaving only a scar. However, it is not wise to be careless as it can spread and cause bacteremia.

Tuberculosis

It is a pathology that affects the respiratory tract and is caused by a strict aerobic bacterium, Mycobacterium tuberculosis. The bacteria are found in the secretions of those who suffer from the disease, specifically in the one they expel when they cough. Contact with these secretions is the most common route of infection.

The symptoms of tuberculosis are:

• Constant cough with bloody sputum
• Fever
• General discomfort
• Chest pain, especially when coughing and breathing
• Profuse sweating at night.

Leprosy

It is a well-known disease caused by another bacterium of the genus Mycobacterium, Mycobacterium leprae. This is a disease that for centuries has been a scourge, since those who suffered from it were execrated from society and forced to live apart.

The most common symptoms of leprosy are:

• Light-colored lesions on the skin
• Bumps or nodules on the skin
• Loss of sensation in certain areas
• Thickening of the skin

Over time, the clinical picture worsens, causing the individual to lose the functionality of their upper and lower limbs, disfigurement caused by skin lesions and discomfort at the skin level, such as a constant burning sensation on the skin.

References

1. Camacho, A., Giles, M., Ortegón, M., Palao, M., Serrano, B. and Velásquez, O. (2009) Techniques for the microbiological analysis of food. UNAM Mexico 2nd edition.
2. Carrol, K., Hobden, J., Miller, S., Morse, S., Mietzner, T., Detrick, B., Mitchell, T. and Sakanari, J. Medical Microbiology. Mc Graw and Hill. 27th edition
3. Dorronsoro, I. and Torroba L. Microbiology of Tuberculosis. (2007). Annals of the Navarra Health System. 30 (2).
4. González, P. and Cona, E. (2006). Nocardia asteroides. Chilean journal of infectology. 2. 3. 4).
5. Hernández, P., Mayorga, J. and Pérez, E. (2010). Actinomycetoma due to Nocardia brasiliensis. Annals of Pediatrics. 73 (4). 159-228
6. Ryan, K. and Ray, C. (2004). Sherris Medical Microbiology. Mc Graw Hill. 4th edition.