What are bacteria?

The word bacteria comes from a Greek term meaning “cane”. It is a prokaryotic unicellular microorganism that can cause diseases, fermentation or putrefaction in living beings or organic matter.


Bacteria are the organisms that abound most on the planet earth and to which we can find them in the most diverse habitats, even those that suppose the most unfavorable conditions for the subsistence of any living organism.

Where are the bacteria?

From the ground, hot and acid springs, followed by radioactive waste, even in the depths of the seas, the earth’s crust and in the most inhospitable places of outer space, are some of the places where we can very easily find ourselves with the tiny bacteria.

Approximately and to give an idea of the proliferation of these and that is not a pure story, it has been calculated that there are 40 million bacterial cells in one gram of soil and one million in a milliliter of fresh water.

On the other hand, in the very human body we find that there are ten times as many bacterial cells as human cells, many of them residing in the digestive tract and the skin, however, the immune system available to humans makes the action of these is practically harmless and even in some cases even beneficial.

Meanwhile, there are some pathogenic bacteria that are the vehicle of dangerous bacterial infections such as cholera, syphilis, leprosy, typhus, diphtheria and scarlet fever, but it will be bacterial respiratory infections that can cause death to humans, as is the case of tuberculosis.


The bacterium is the smallest unicellular organism that exists on Earth, belongs to the monera kingdom, is characterized by having a prokaryotic cell, in which its genetic material is usually grouped in a nuclear region that lacks its own membrane or envelope; that is, it has no nucleus or cellular organelles (mitochondria, chloroplasts, etc.).

Due to their shape, the bacteria can be classified into: bacilli (elongated or rod-shaped), vibrios (curved), espililos (wavy or in the form of spirals) and coccos (rounded).

The latter can be isolated, in pairs (diplococci), in aligned groups (streptococci), in irregular masses (staphylococci) or in cubic masses (sarcina).

Because they are prokaryotic cells, they lack a nucleus or internal organelles. On the other hand, although the term comes from a cane, the bacteria can have the shape of a rod, sphere or helix.

Bacteria can be classified into different groups based on a different criterion. Thus, for example, if we start with what its form is, we find the fact that there are four clearly delimited types:

Big size

Bacillus They are the bacteria that are defined by being elongated and because they have the possibility of being curved or straight. In the same way, we must underline the fact that they may or may not have flagella.

Leptothrix. Of great size are those that are framed under this denomination and have as their main hallmark that they may have filaments called tabicados.

Espirilos. In this case, under said category bacteria that have a helical curved appearance are included.

Cocos Bacteria that are named are those that have a rounded shape and have the possibility that they can be isolated, in pairs or in the form of a clustered chain.

The Oxygen

In addition to the above, we must also emphasize the fact that bacteria can also be classified based on what their breathing is.

In this case, we could make two large groups: aerobic, which are those that make use of oxygen, and anaerobic, which do not use that but other elements such as carbonate, for example.

Third, we can determine that the bacteria can be classified equally taking into account what is your need for growth. A fact that would lead to encounter two types of bacteria: heterotrophic (parasitic, putrefactive, symbiotic …) and autotrophic (photosynthesizing, chemosynthetic …).

The habitat

Bacteria can live in any habitat; even some species survive in outer space. These characteristics make bacteria the most abundant organism in the world: 40 million bacterial cells can coexist in just one gram of soil.

The body of the human being lodges ten bacterial cells by each human cell. The immune system allows most bacteria to be harmless or even beneficial (they help digestion, for example). However, certain bacteria can cause serious diseases such as tuberculosis, leprosy, and cholera.

Bacteria help in the production of cheese, butter and yogurt, perform important functions in the manufacture of certain medicines and collaborate in the treatment of wastewater. They are also used for tanning leather and curing tobacco.


The discipline responsible for the study of bacteria is known as bacteriology. It is a branch of microbiology, the science that is dedicated to studying microorganisms. Bacteriology and microbiology belong to the field of biology.

These scientific fields have advanced thanks to technological advances, although it is estimated that we only know 1% of the microbes in the biosphere.


Bacteria also have a variety of differences in their nutrition, ability to use different forms of energy and chemical structure of their cell wall. Some are heterotrophic, do not require a source of food to survive, and others are autotrophic (photosynthesizing or chemosynthesizing) capable of obtaining energy from simple substances.

The heterotrophic bacteria together with the fungi enrich the soils and favor the vegetal development, because they decompose the organic matter, thus playing a fundamental role in the ecosystems.


A large number of bacteria are those that produce some more common and dangerous diseases that affect living beings such as cholera, syphilis, pneumonia, tetanus, typhus, diphtheria, etc.

However, it should be noted that some bacteria are useful, help to degrade digested foods and others are capable of producing antibiotics and are used in scientific research specifically in biotechnology and genetic engineering.

On the other hand, bacteria have a wide industrial use in the manufacture of cheese, yogurt, and dairy products, as a result of the lactic fermentation process; wine, beer, and other alcoholic beverages, obtained in alcoholic fermentation; the vinegar or acetic acid, obtained in acetic fermentation, and also in the production of citric acid, acetone, among others.

Pathogenic bacteria

There are some pathogenic bacteria that are the vehicle of dangerous bacterial infections such as cholera, syphilis, leprosy, typhus, diphtheria and scarlet fever, but it will be bacterial respiratory infections that can cause death to humans, as is the case of tuberculosis.

To counteract the harmful effect of some bacteria, antibiotics will usually be used since they are the only ones that inhibit the formation of their cell walls and even stop some of their life cycles.

But, paradoxically, bacteria are essential in some tasks such as the recycling of certain elements, for some industrial processes, such as the treatment of wastewater and in the food industry for the production of cheeses, yogurts, butter, vinegars, among others.

Also, the manufacture of some medicines and other chemical products depend on the presence of these for their realization.

Bacteriology, a branch of microbiology deals with the study of bacteria.

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