Bacteria, why do they make me sick?/What are bacteria?
CHAPTER 1
WHAT ARE
BACTERIA?
Before starting,
How would you define a bacterium?
What bacteria do you know?
What are bacteria?
Bacteria are microscopic organisms that lack a defined or structured nucleus. These organisms are classified as prokaryotes.
Structure of a bacterium
Bacterial cells range in size from 0.5 to 5 μm (1 μm is 0.0001 cm). It has a cytoplasm enclosed by a plasma membrane. The outermost layer is the cell wall that varies depending on the type of bacteria. The bacterial genome consists of a long DNA filament, circular and closed, called nucleoid, which is compacted in the cytoplasm and lacks a membrane. The cytoplasm also contains many ribosomes, and in some cases, inclusion bodies. Some bacterial cells also have a capsule, flagellum and fimbriae (also called pili).
There are different criteria to classify bacteria.
Most of the bacteria are harmless to humans or are part of our normal bacterial microbiota, either in the skin or mucosae, protecting us from getting a disease.
Bacteria are classified using different criteria. We can classify them in pathogenic and nonpathogenic; we can also distinguish them based on its morphology, its type of arrangement and also based on its optimal temperature of growth, cell wall and how they respond to oxygen levels.
Can all bacteria make me sick?
The diversity of bacteria is astonishing. In fact, it is believed that the biodiversity of organisms known today, it is only a small percentage of the totality of microorganisms that have not been discovered yet. However, the diversity known today, can be divided into two main groups”
1. Beneficial bacteria. 2. Pathogenic bacterias.
Beneficial bacteria
MICROBIOTA
Human beings are the habitat of a wide variety of microorganisms named native microbiota. These microorganisms are not only harmless to the host, but they also protect them against pathogenic bacteria, fungi, and viruses that compete for the same available space and nutrients. Microbiota composition depends on different factors, among which we can highlight the following:
• Personal hygiene
• Diet
• Hydration level
• Drugs use (especially antibiotics)
• Exposure to environmental toxins.
The digestive tract is an example of the importance of the microbiota because, without it, it would be impossible to have a healthy digestive system, due to its contribution to metabolize bile acids and to synthesize vitamins.
In this way, drinking purified or chlorinated water, having a diet with a high or low content of fiber, sugar or fat, may select different intestinal bacteria due to their capacity to use mineral and essential nutrients.
MICROBIOME
The microbiome is defined as the microorganisms located normally in different parts of the body of multicellular organisms, such as the human body. In this way, the normal microbiome characterizes health, and its alterations may indicate there is a disease. These changes may be harmless when the microbiome and its basic functional properties remain present, but when these functions are lost, diseases may appear.
The information obtained from the study of the different microbiome has added a new concept of disease, one that is caused by a community of microorganisms and not by a particular pathogen. This new definition goes beyond the traditional infectious diseases and it may include immune and metabolic disorders, such as inflammatory bowel disease, obesity, type 2 diabetes, and celiac disease.
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Most of the bacteria that colonize the
bowel belong to the phylum Actinobacteria, Bacteroidetes and Firmicutes. To establish their niche, some bacteria use antibacterial peptides, bacteriocins or metabolite that prevents the proliferation of other competitive species. These molecules are also beneficial to the host because they eliminate invasive bacteria such as Salmonella spp., Shigella spp., Clostridium difficile, Bacillus cereus, and other pathogens. |
Pathogenic bacteria
Pathogenic bacteria are those that can cause infections in humans or animals and have different virulence factors, which are:
| Proteins that contribute to the virulence of the bacteria over the eukar- yotic cell, which enables infection. |
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Interaction mechanisms with mammalian cells. |
Currently, it is known that evolution and spread of virulence factors, which are those that enable a bacterium to be harmful to the human body, are facilitated but the pathogenicity islands. These islands are one or more genes are related to virulence, and mobility genes, such as integrases or transposons.
PATHOGENICITY ISLANDS
Mobile genetic elements that contribute to spread and modify virulence, and they also mediate the movement of different genes that encode virulence factors.