The anaerobic bacteria They are those that do not use oxygen in their metabolic processes. In fact, many of these bacteria cannot survive in environments where this element is present, as it is toxic to them..
One of the metabolic processes carried out by this type of bacteria and that has been most widely studied is fermentation. This is a process that has a large number of applications at an industrial level, related to the production of alcoholic beverages, yogurt and vinegar, among other products..
Similarly, many of these bacteria have their natural habitat within the human body, being found mainly in the gastrointestinal tract. Some are harmless, but others cause various pathologies in the body, many of which can lead to death.
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Anaerobic bacteria are among the first living things to emerge on the planet. Importantly, thousands of years ago, when the first life forms began to emerge, oxygen levels in the atmosphere were really low. Due to this, the first organisms that were developed had other cellular mechanisms to obtain energy.
In fact, for many of the species that make up the group of anaerobic bacteria, oxygen is highly toxic. This is why some bacteria are found in habitats in which there is no oxygen present..
Likewise, there are anaerobic bacteria that support living in the presence of very small amounts of oxygen, so they can be located in a greater variety of environments. Some of these bacteria are part of the regular microbiota of the human being, specifically at the level of the oral cavity and the gastrointestinal tract..
On the other hand, these bacteria carry out fermentation. This is a catabolic process by which organic compounds are degraded to simpler ones in the absence of oxygen. It is made mainly by anaerobic bacteria.
Likewise, there is no single type of fermentation. Depending on the product obtained there are several types, such as acetic, lactic and alcoholic fermentation, among others..
In these bacteria, the various enzyme systems function perfectly in the absence of oxygen. This is because they use other compounds such as fumarate, nitrate or sulfate as electron acceptors..
It is worth mentioning that many of the anaerobic bacteria are human pathogens. Among the best known and most studied we can mention the species of the genera Porphyromonas, Clostridium Y Prevotella, among other.
Many of the anaerobic bacteria cannot resist being in environments in which there is oxygen, because this is toxic for them. However, there are also some, despite not using oxygen, they can survive in environments where there are different concentrations of this gas.
With this in mind, anaerobic bacteria can be divided into three types: obligate anaerobic, aerotolerant, and facultative anaerobic..
They are also known as strict anaerobic bacteria. They are those that do not use oxygen for any metabolic process. Your tolerance to this gas is variable. According to this, obligate anaerobic bacteria are classified as:
- Strict: tolerate only oxygen concentrations below 0.5%.
- Moderate: can tolerate oxygen concentrations ranging from 2 to 8%.
These are bacteria that, although they do not use oxygen to carry out any cellular process, can live in habitats where it is present. A classic example of this type of bacteria is the Pronibacterium acnespio, causing many cases of acne.
Facultative anaerobic bacteria do not use oxygen for their metabolic processes, but they can live in the presence of it, since it is not toxic to them. They mainly carry out the fermentation process to obtain the necessary energy. Among the best known facultative anaerobic bacteria are the Escherichia coli and the Staphylococcus aureus.
To facilitate the study of anaerobic bacteria, they can be grouped according to their shape and staining into: gram negative cocci, gram positive cocci, gram negative bacilli and gram positive bacilli.
Within this group are several genres such as Veillonella Y Megasphaera.
This is a genus of gram negative bacteria widely recognized for their fermentative potential. These bacteria ferment lactate to acetate and propionate through a metabolic pathway known as the methylmalonyl-CoA pathway..
Likewise, they are an integral part of the microbiota of certain parts of the body, such as the oral cavity and the gastrointestinal tract..
They are bacteria with a rounded shape that, when stained with the gram pigment, adopt a characteristic violet color..
Bacteria of this genus are found as part of the bacterial flora of the human body. However, it is possible that it is the cause of certain pathological processes. This bacterium has been isolated from vaginal discharge, ovarian abscesses, and certain chronic wounds..
Likewise, in different clinical case studies it has been established that species of this genus can cause a wide range of infections in the urinary tract, as well as in the blood..
It is a genus of bacteria that frequently cause the development of pathologies in humans. In addition, they are part of the microbiota of certain mucous membranes of the body, such as the oropharyngeal and genitourinary..
They are bacteria that have an elongated rod shape and are characterized by acquiring a fuchsia color when subjected to the Gram staining process. This group of anaerobic bacteria encompasses several genera.
It is a genus of bacteria that are frequently found as components of the bacterial flora of the oral cavity, the gastrointestinal tract, and the vaginal cavity. Despite this, when normal body conditions change, these bacteria proliferate uncontrollably.
When this occurs, Prevotella They cause the development of certain infections, the most common being those that occur at the level of the periodontal mucosa. They have also been isolated from patients with rheumatoid arthritis..
To this group belong rod-shaped bacteria that have a thick layer of peptidoglycan in their cell wall that retains the gram dye particles, giving it a violet color. A wide variety of species that cause various diseases and pathologies in humans belong to this group..
It is a gram positive bacterium that is characterized by producing spores, which constitute an infectious agent for humans. In the same way, this bacterium synthesizes and releases certain toxins, whose main function is to paralyze the muscles..
Among the diseases that this bacterium generates, we can mention food botulism, which affects the gastrointestinal tract, and infant botulism, which affects young children and is caused by the direct ingestion of spores..
This bacterium is well known in the medical field and has been the subject of numerous studies on the effects it generates in the body. Like the rest of the bacteria of the genus Clostridium, this bacterium produces endospores, which are very resistant to environmental components.
Likewise, this bacterium causes in humans a pathology known as tetanus. This disease is caused by the entry of spores into the body, which germinate and begin to synthesize and release the toxins of this species..
When this happens, the spores interfere with the transmission of nerve impulses, causing the muscles to spasm..
The main difference between anaerobic bacteria and aerobic bacteria refers to the use of oxygen and the ability to develop in the presence or absence of this element..
In this sense, anaerobic bacteria do not use oxygen for any of their internal energy production processes. On the contrary, aerobic bacteria do use it as an electron acceptor during the process of cellular respiration, by means of which they degrade molecules of organic compounds such as glucose, obtaining a large amount of energy.
Likewise, there are anaerobic bacteria that, apart from not using oxygen in their various processes, cannot be in oxygen-rich environments either, since this element is highly toxic to them. Instead of cellular respiration, they run fermentation.
Another notable difference between the two types of cells has to do with their habitat. Aerobic bacteria are found in environments where oxygen is widely available, while aneroid bacteria survive in environments where there is a complete absence of oxygen or where oxygen concentrations are very low..
The cultivation of anaerobic bacteria is a process in which all the necessary precautions must be followed to avoid making a mistake. Here it is important to bear in mind that some species of anaerobic bacteria cannot have any type of contact with oxygen, since this can be a toxic agent for them..
One of the elements to take into account when a culture is to be carried out in the laboratory is the culture medium that should be used. Each group of bacteria has certain specific requirements.
Currently there are many culture media that can be used for the sowing of any type of bacteria. In the specific case of anaerobic bacteria, the culture medium requires the addition of a reducing agent, such as thioglycollate or cysteine..
Likewise, to optimize the results that are expected to be obtained, a redox indicator can be added, which shows the possible presence of oxygen, such as resazurin..
The most widely used and recommended culture media for seeding anaerobic bacteria are:
- Anerobium blood agar: contains, among other things, meat extract, yeast extract, NaCl, glucose and peptone, among others.
- Chocolate agar: it is not widely used to cultivate anaerobic bacteria. However, thanks to its components it is possible to make them grow there.
- Phenyl Ethyl Alcohol Agar with Blood - This medium is widely used to properly isolate anaerobic bacteria.
- Columbia agar with colistin and nalidixic acid.
- Thioglycollate: it is generally enriched with L-cystine, hemin and vitamin K.
- KVLB agar (kanamycin, vancomycin, lacquered blood): specifically for gram negative bacilli.
Once the culture medium to be used has been selected, according to the bacteria to be cultivated, the procedure can begin. In this sense, a totally anaerobic environment must be created, in which there is no oxygen. To achieve this, two procedures can be followed:
- Sodium hydroxide - pyrogallic acid method: this method is based on obtaining an anaerobic environment through a chemical reaction, using, instead of a reducing agent, a catalyst. It is a delicate and potentially dangerous procedure.
- Use of anaerobic flasks: this type of flasks are very useful for the cultivation of anaerobic organisms. However, it is only used with organisms that can withstand light contact with small levels of oxygen..
Likewise, a kind of vacuum must be created to proceed with cultivation. This can be done in several ways: displacing oxygen with other gases, absorbing oxygen through chemical or biological methods, or using reducing agents..
Once these steps have been carried out, inoculation is carried out to incubate the culture and wait for the reasonable time to study the colonies obtained. The waiting time will depend on the species that is being cultivated.
There are fast growing species (18-24 hours) such as Clostridium perfringens and there are others that have slow growth (5-7 days) such as Propionibacterium.
These methods are used to find out the approximate number of microorganisms found in a culture. In the case of anaerobic bacteria, there are several techniques that allow counting.
However, since many of these bacteria cannot come into direct contact with oxygen because it is toxic, extreme care must be taken when putting these techniques into practice..
In this sense, two methods will be described here: the most probable number (for strict aerobics) and the plaque spreading method (for facultative and microaerophilic anaerobes).
This technique is based on the determination of the presence or absence of microorganisms in a sample. This is done in replicates of consecutive solutions. The principle behind this method is that a single living cell can develop, thus producing a cloudy culture..
To carry out this process, it is necessary to make a series of serial dissolutions of the culture sample. For this, it is important to use a liquid culture medium with the nutritional requirements. Once this is done, the test tubes are incubated waiting for the microorganisms to grow.
After the reasonable period of time, test tubes in which one or more bacterial cells were inoculated will appear cloudy..
As the tubes in which the dissolution factor increases are reviewed, they become progressively less cloudy, since they contain fewer and fewer bacterial cells. This is the case until reaching a point where there will no longer be any microorganisms or only one.
Finally, the population density estimate is obtained from the pattern of occurrence in serial solutions and through the use of a standard probabilistic table that has been designed for this purpose..
This is a fairly straightforward method. First, several Petri dishes with the culture medium should be arranged in an orderly manner. Subsequently, the inoculation of 1 mL of solution is carried out in each capsule. It is important to note that the solutions contain the microorganism to be counted..
Then, with the help of a glass rod, the inoculated material is spread homogeneously covering the entire surface of the culture medium..
Finally, the Petri dishes are incubated under the conditions required for the time necessary for each type of microorganism. Finally, the colonies that have been generated are counted.
Many of the anaerobic bacteria are known pathogens for man and produce diseases and pathologies that can even compromise the life of the individual..
The oral cavity is the ideal environment for many anaerobic bacteria, which proliferate there and generate certain pathologies such as periodontitis, necrotizing gingivitis and abscesses, among others..
Most of these infections present with pain, mucosal lesions and suppuration of pus, with the consequent increase in body temperature.
Among the causative bacteria, Porphyromonas gingivalis it is the one most frequently isolated in these lesions.
One of the routes of infection of this type of bacteria is through ingestion, either spores (in the case of sporulated bacteria) or contaminated food and water..
In these cases, the bacteria anchor to the intestine and begin to damage the intestinal mucosa, triggering symptoms such as: fever, abdominal pain, liquid stools, bloating, nausea and general malaise..
The anaerobic bacteria that can generate this clinical picture are Clostridium difficile Y Escherichia coli, among other.
Some of these bacteria, when they come into contact with an open wound, can infect it. If this occurs, severe skin infections can be generated, such as gas gangrene, whose causative agent is Clostridium perfringes.
Symptoms of gas gangrene include: blisters filled with bloody fluid, subcutaneous emphysema, severe pain and high fever, among others.
Another pathology caused by anaerobic bacteria at the cutaneous level is necrotizing fasciitis, in which the infection spreads beyond the skin tissue, affecting even the fascia that surrounds the muscles..
Symptoms include acute pain, severe erythema, blisters, and most often gangrene. Among the causative agents of this pathology is the Staphylococcus aureus.
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