Intracellular bacteria are

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

that have the capability to enter and survive within the cells of the host organism. These bacteria include many different pathogens that live in the cytoplasm and nuclei of the host cell's they inhabit. ''Mycobacterium tuberculosis'' is an example of an intracellular bacterial species. There are two types of intracellular bacteria: facultative intracellular bacteria, which can grow extracellularly or intracellularly, and obligate intracellular bacteria, which can grow only intracellularly.

Facultative intracellular bacteria

Examples of facultative intracellular bacteria include members of the genera ''

Brucella ''Brucella'' is a genus of Gram-negative bacterium, bacteria, named after David Bruce (microbiologist), David Bruce (1855–1931). They are small (0.5 to 0.7 by 0.6 to 1.5 μm), non-Bacterial capsule, encapsulated, non-motile, facultatively ...

'', ''

Legionella ''Legionella'' is a genus of gram-negative bacteria, gram-negative bacteria that can be seen using a silver stain or grown in a special media that contains cysteine, an amino acid. It is known to cause legionellosis (all illnesses caused by ''Legi ...

'', ''

Listeria ''Listeria'' is a genus of bacteria that acts as an intracellular parasite in mammals. As of 2024, 28 species have been identified. The genus is named in honour of the British pioneer of sterile surgery Joseph Lister. ''Listeria'' species ...

'', and ''

Mycobacterium ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (''Mycobacterium tuberculo ...

''. These bacteria invade the human body and replicate inside the cells, evading the immune system and causing disease by disrupting the human's cells normal function. Diseases caused by facultative intracellular bacteria include Listeriosis ''(Listeria monocytogenes)'', Typhoid Fever ''(Salmonella typhi)'', Legionnaires' disease ''(Legionella pneumophila)'', and Salmonellosis ''(Salmonella enterica)'' to name a few. While they can invade the human body, they are also capable of living extracellularly. These bacteria can replicate within the environment, sustain their metabolic state, and survive harsh conditions by using mechanisms such as a bacterium-containing vacuole, lysosome resistance, and entering a survival state called persistence.

Obligate intracellular bacteria

Examples of obligate intracellular bacteria include members of the order

Rickettsiales The Rickettsiales, informally called rickettsias, are an order of small Alphaproteobacteria. They are obligate intracellular parasites, and some are notable pathogens, including '' Rickettsia'', which causes a variety of diseases in humans, and ...

and members of the genus ''

Mycoplasma ''Mycoplasma'' is a genus of bacteria that, like the other members of the class ''Mollicutes'', lack a cell wall, and its peptidoglycan, around their cell membrane. The absence of peptidoglycan makes them naturally resistant to antibiotics ...

''. These bacteria need the human host to be able to reproduce and when they have invaded the body, they cause disease. Unlike facultative intracellular bacteria that can grow within or outside of a host's body, obligate bacteria cannot survive without host cells. These bacteria cannot reproduce outside of the host cell because they lack the metabolic processes and enzymes needed to reproduce, which the host cell gives them. Diseases caused by obligate intracellular bacteria include chlamydia ''(Chlamydia trachomatis)'' and Rocky Mountain Spotted Fever ''(Rickettsia rickettsii)''.

Infectious pathways

Hosts usually come into contact with the bacteria through the skin, but there are chances of contracting the bacteria from a bite, such as that of ticks, mites, and/or mosquitoes ''(Rickettsia rickettsii).'' ''Listeria monocytogenes'' is found in soil, water, and also decaying animals and plants. It is generally transmitted through food being processed or handled in areas contaminated with ''L. monocytogenes''. ''Legionella pneumoniae'' are found in aquatic conditions, such as artificial water systems, like that of hot tubs and showers. ''Salmonella typhi'' and ''Salmonella enterica'' are both transmitted orally through feces or through food and/or water that has the bacteria. ''Chlamydia trachomatis'' is spread by having unprotected sex. ''Mycobacterium tuberculosis'' is spread through the air when being near anyone with tuberculosis.

References

Bacteria Microbiology Infectious diseases Cells {{Bacteria-stub

Facultative intracellular bacteria

Obligate intracellular bacteria

Infectious pathways

See also

References