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Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some micro-animals and plants. Viruses are generally regarded as not living and therefore not considered to be microorganisms, although a subfield of microbiology is virology , the study of viruses.
Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, [4] particularly the ones in the gut. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague.
Although the vast majority of bacteria are harmless or beneficial to one's body, a few pathogenic bacteria can cause infectious diseases. The most common bacterial disease is tuberculosis , caused by the bacterium Mycobacterium tuberculosis , which affects about 2 million people mostly in sub-Saharan Africa.
By contrast, several thousand species are part of the gut flora present in the digestive tract. [citation needed] The body is continually exposed to many species of bacteria, including beneficial commensals, which grow on the skin and mucous membranes, and saprophytes, which grow mainly in the soil and in decaying matter. The blood and tissue ...
In plants, injuries result from the eating of plant parts by herbivorous animals including insects and mammals, [10] from damage to tissues by plant pathogens such as bacteria and fungi, which may gain entry after herbivore damage or in other ways, [11] and from abiotic factors such as heat, [12] freezing, [13] flooding, [14] lightning, [15 ...
While tetanus toxin is produced from Clostridium tetani, a spore forming bacteria found in soil, Tetanus is a paralytic disease that is global and commonly affects newborns as well as non-immunized individuals. Tetanus enters the body of organisms through wounds or skin breaks and can be found in manure, soil, and dust.
One example of this in humans is E. coli. Normally, this bacteria flourishes as a part of the normal, healthy microbiota in the intestines. However, if it relocates to a different region of the digestive tract or the body, it can cause intense diarrhea. So, while E. coli is classified as a pathogen, but it does not always act as such. [9]
Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. [1] The pathogenicity of an organism—its ability to cause disease—is determined by its virulence factors.