Intracellular bacteria are bacteria that have the capability to enter and survive within the cells of the host organism. [1] These bacteria include many different pathogens that live in the cytoplasm and nuclei of the host cell's they inhabit. Two examples of intracellular pathogenic bacteria are Mycobacterium tuberculosis and also Toxoplasma gondii. [2] 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. [3]
Examples of facultative intracellular bacteria include members of the genera Brucella , Legionella , Listeria , and Mycobacterium . 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. [3] 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. [4]
Examples of obligate intracellular bacteria include members of the order Rickettsiales and members of the genus Mycoplasma . [1] 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. [3] Diseases caused by obligate intracellular bacteria include Chlamydia (Chlamydia trachomatis), Rocky Mountain Spotted Fever (Rickettsia rickettsii), and Tuberculosis (Mycobacterium tuberculosis) to name a few. [3]
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). [5] 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. monocygotenes. [6] Legionella pneumoniae are found in aquatic conditions, such as artificial water systems, like that of hot tubs and showers. [7] Salmonella typhi and Salmonella enterica are both transmitted orally through feces or through food and/or water that has the bacteria. [8] Chlamydia trachomatis is spread by having unprotected sex. [9] Mycobacterium tuberculosis is spread through the air when being near anyone with tuberculosis. [10]
Salmonella is a genus of rod-shaped, (bacillus) gram-negative bacteria of the family Enterobacteriaceae. The two known species of Salmonella are Salmonella enterica and Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,650 serotypes. Salmonella was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon.
Salmonella enterica is a rod-shaped, flagellate, facultative anaerobic, Gram-negative bacterium and a species of the genus Salmonella. It is divided into six subspecies, arizonae (IIIa), diarizonae (IIIb), houtenae (IV), salamae (II), indica (VI), and enterica (I). A number of its serovars are serious human pathogens; many of them are serovars of Salmonella enterica subsp. enterica.
Listeria monocytogenes is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in the presence or absence of oxygen. It can grow and reproduce inside the host's cells and is one of the most virulent foodborne pathogens. Twenty to thirty percent of foodborne listeriosis infections in high-risk individuals may be fatal. In the European Union, listeriosis continues an upward trend that began in 2008, causing 2,161 confirmed cases and 210 reported deaths in 2014, 16% more than in 2013. In the EU, listeriosis mortality rates also are higher than those of other foodborne pathogens. Responsible for an estimated 1,600 illnesses and 260 deaths in the United States annually, listeriosis ranks third in total number of deaths among foodborne bacterial pathogens, with fatality rates exceeding even Salmonella spp. and Clostridium botulinum.
An asymptomatic carrier is a person or other organism that has become infected with a pathogen, but shows no signs or symptoms.
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 are Gram-positive, rod-shaped, and facultatively anaerobic, and do not produce endospores.
Listeriosis is a bacterial infection most commonly caused by Listeria monocytogenes, although L. ivanovii and L. grayi have been reported in certain cases. Listeriosis can cause severe illness, including severe sepsis, meningitis, or encephalitis, sometimes resulting in lifelong harm and even death. Those at risk of severe illness are the elderly, fetuses, newborns, and those who are immunocompromised. In pregnant people, it may cause stillbirth or spontaneous abortion, and preterm birth is common. Listeriosis may cause mild, self-limiting gastroenteritis and fever in anyone.
Rickettsia rickettsii is a Gram-negative, intracellular, cocco-bacillus bacterium that was first discovered in 1902. Having a reduced genome, the bacterium harvests nutrients from its host cell to carry out respiration, making it an organo-heterotroph. Maintenance of its genome is carried out through vertical gene transfer where specialization of the bacterium allows it to shuttle host sugars directly into its TCA cycle.
In cell biology, a phagosome is a vesicle formed around a particle engulfed by a phagocyte via phagocytosis. Professional phagocytes include macrophages, neutrophils, and dendritic cells (DCs).
Brucella is a genus of Gram-negative bacteria, named after David Bruce (1855–1931). They are small, non-encapsulated, non-motile, facultatively intracellular coccobacilli.
Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. They are also called intracellular pathogens.
A subclinical infection—sometimes called a preinfection or inapparent infection—is an infection by a pathogen that causes few or no signs or symptoms of infection in the host. Subclinical infections can occur in both humans and animals. Depending on the pathogen, which can be a virus or intestinal parasite, the host may be infectious and able to transmit the pathogen without ever developing symptoms; such a host is called an asymptomatic carrier. Many pathogens, including HIV, typhoid fever, and coronaviruses such as COVID-19 spread in their host populations through subclinical infection.
Listeriolysin O (LLO) is a hemolysin produced by the bacterium Listeria monocytogenes, the pathogen responsible for causing listeriosis. The toxin may be considered a virulence factor, since it is crucial for the virulence of L. monocytogenes.
Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. By contrast, several thousand species are part of the gut flora present in the digestive tract.
The gentamicin protection assay or survival assay or invasion assay is a method used in microbiology. It is used to quantify the ability of pathogenic bacteria to invade eukaryotic cells.
Viable but nonculturable (VBNC) bacteria refers as to bacteria that are in a state of very low metabolic activity and do not divide, but are alive and have the ability to become culturable once resuscitated.
PATRIC was a bacterial bioinformatics website from the Bioinformatics Resource Center, originally created in 2004. It has since been combined with the Influenza Research Database and the Virus Pathogen Database and Analysis Resource Center to create the Bacterial and Viral Bioinformatics Resource Center (BV-BRC). It is an information system that integrates databases and analysis tools. It focuses on various data related to bacterial pathogens. PATRIC facilitates integration of various types of pathogen information to support biomedical research on bacterial infectious diseases.
Host-directed therapeutics, also called host targeted therapeutics, act via a host-mediated response to pathogens rather than acting directly on the pathogen, like traditional antibiotics. They can change the local environment in which the pathogen exists to make it less favorable for the pathogen to live and/or grow. With these therapies, pathogen killing, e.g.bactericidal effects, will likely only occur when it is co-delivered with a traditional agent that acts directly on the pathogen, such as an antibiotic, antifungal, or antiparasitic agent. Several antiviral agents are host-directed therapeutics, and simply slow the virus progression rather than kill the virus. Host-directed therapeutics may limit pathogen proliferation, e.g., have bacteriostatic effects. Certain agents also have the ability to reduce bacterial load by enhancing host cell responses even in the absence of traditional antimicrobial agents.
Nucleomodulins are a family of bacterial proteins that enter the nucleus of eukaryotic cells.
Milk borne diseases are any diseases caused by consumption of milk or dairy products infected or contaminated by pathogens. Milk-borne diseases are one of the recurrent foodborne illnesses—between 1993 and 2012 over 120 outbreaks related to raw milk were recorded in the US with approximately 1,900 illnesses and 140 hospitalisations. With rich nutrients essential for growth and development such as proteins, lipids, carbohydrates, and vitamins in milk, pathogenic microorganisms are well nourished and are capable of rapid cell division and extensive population growth in this favourable environment. Common pathogens include bacteria, viruses, fungi, and parasites and among them, bacterial infection is the leading cause of milk-borne diseases.
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