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Staphylococcus aureus is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe that can grow without the need for oxygen. Although S. aureus usually acts as a commensal of the human microbiota, it can also become an opportunistic pathogen, being a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning. Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. S. aureus is one of the leading pathogens for deaths associated with antimicrobial resistance and the emergence of antibiotic-resistant strains, such as methicillin-resistant S. aureus (MRSA), is a worldwide problem in clinical medicine. Despite much research and development, no vaccine for S. aureus has been approved.
An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell. Gram negative pathogens may secrete outer membrane vesicles containing lipopolysaccharide endotoxin and some virulence proteins in the bounding membrane along with some other toxins as intra-vesicular contents, thus adding a previously unforeseen dimension to the well-known eukaryote process of membrane vesicle trafficking, which is quite active at the host–pathogen interface.
An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines. They can be chromosomally or plasmid encoded. They are heat labile (>60⁰), of low molecular weight and water-soluble. Enterotoxins are frequently cytotoxic and kill cells by altering the apical membrane permeability of the mucosal (epithelial) cells of the intestinal wall. They are mostly pore-forming toxins, secreted by bacteria, that assemble to form pores in cell membranes. This causes the cells to die.
Guanylate cyclase 2C, also known as guanylyl cyclase C (GC-C), intestinal guanylate cyclase, guanylate cyclase-C receptor, or the heat-stable enterotoxin receptor (hSTAR) is an enzyme that in humans is encoded by the GUCY2C gene.
Bacteroides is a genus of Gram-negative, obligate anaerobic bacteria. Bacteroides species are non endospore-forming bacilli, and may be either motile or nonmotile, depending on the species. The DNA base composition is 40–48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids. They also contain meso-diaminopimelic acid in their peptidoglycan layer.
Bacteroides fragilis is an anaerobic, Gram-negative, pleomorphic to rod-shaped bacterium. It is part of the normal microbiota of the human colon and is generally commensal, but can cause infection if displaced into the bloodstream or surrounding tissue following surgery, disease, or trauma.
Virulence factors are cellular structures, molecules and regulatory systems that enable microbial pathogens to achieve the following:
Cholera toxin is an AB5 multimeric protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the massive, watery diarrhea characteristic of cholera infection. It is a member of the heat-labile enterotoxin family.
A disintegrin and metalloprotease 17 (ADAM17), also called TACE, is a 70-kDa enzyme that belongs to the ADAM protein family of disintegrins and metalloproteases.
Inflammasomes are cytosolic multiprotein oligomers of the innate immune system responsible for the activation of inflammatory responses. Activation and assembly of the inflammasome promotes proteolytic cleavage, maturation and secretion of pro-inflammatory cytokines interleukin 1β (IL-1β) and interleukin 18 (IL-18), as well as cleavage of gasdermin D. The N-terminal fragment resulting from this cleavage induces a pro-inflammatory form of programmed cell death distinct from apoptosis, referred to as pyroptosis, and is responsible for secretion of the mature cytokines, presumably through the formation of pores in the plasma membrane. Additionally, inflammasomes can be incorporated into larger cell death-inducing complexes called PANoptosomes, which drive another distinct form of pro-inflammatory cell death called PANoptosis.
Clostridium difficile toxin B is a cytotoxin produced by the bacteria Clostridioides difficile, formerly known as Clostridium difficile. It is one of two major kinds of toxins produced by C. difficile, the other being a related enterotoxin. Both are very potent and lethal.
Clostridium difficile toxin A (TcdA) is a toxin generated by Clostridioides difficile, formerly known as Clostridium difficile. It is similar to Clostridium difficile Toxin B. The toxins are the main virulence factors produced by the gram positive, anaerobic, Clostridioides difficile bacteria. The toxins function by damaging the intestinal mucosa and cause the symptoms of C. difficile infection, including pseudomembranous colitis.
Microbial toxins are toxins produced by micro-organisms, including bacteria, fungi, protozoa, dinoflagellates, and viruses. Many microbial toxins promote infection and disease by directly damaging host tissues and by disabling the immune system. Endotoxins most commonly refer to the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) that are in the outer plasma membrane of Gram-negative bacteria. The botulinum toxin, which is primarily produced by Clostridium botulinum and less frequently by other Clostridium species, is the most toxic substance known in the world. However, microbial toxins also have important uses in medical science and research. Currently, new methods of detecting bacterial toxins are being developed to better isolate and understand these toxins. Potential applications of toxin research include combating microbial virulence, the development of novel anticancer drugs and other medicines, and the use of toxins as tools in neurobiology and cellular biology.
Hathewaya histolytica is a species of bacteria found in feces and the soil. It is a motile, gram-positive, aerotolerant anaerobe. H. histolytica is pathogenic in many species, including guinea pigs, mice, and rabbits, and humans. H. histolytica has been shown to cause gas gangrene, often in association with other bacteria species.
In the field of molecular biology, enterotoxin type B, also known as Staphylococcal enterotoxin B (SEB), is an enterotoxin produced by the gram-positive bacteria Staphylococcus aureus. It is a common cause of food poisoning, with severe diarrhea, nausea and intestinal cramping often starting within a few hours of ingestion. Being quite stable, the toxin may remain active even after the contaminating bacteria are killed. It can withstand boiling at 100 °C for a few minutes. Gastroenteritis occurs because SEB is a superantigen, causing the immune system to release a large amount of cytokines that lead to significant inflammation.
Enteroaggregative Escherichia coli are a pathotype of Escherichia coli which cause acute and chronic diarrhea in both the developed and developing world. They may also cause urinary tract infections. EAEC are defined by their "stacked-brick" pattern of adhesion to the human laryngeal epithelial cell line HEp-2. The pathogenesis of EAEC involves the aggregation of and adherence of the bacteria to the intestinal mucosa, where they elaborate enterotoxins and cytotoxins that damage host cells and induce inflammation that results in diarrhea.
Aureolysin is an extracellular metalloprotease expressed by Staphylococcus aureus. This protease is a major contributor to the bacterium's virulence, or ability to cause disease, by cleaving host factors of the innate immune system as well as regulating S. aureus secreted toxins and cell wall proteins. To catalyze its enzymatic activities, aureolysin requires zinc and calcium which it obtains from the extracellular environment within the host.
Larazotide is a synthetic eight amino acid peptide that functions as a tight junction regulator and reverses leaky junctions to their normally closed state. It is being studied in people with celiac disease.
Bacteroides thetaiotaomicron is a gram-negative, rod shaped obligate anaerobic bacterium that is a prominent member of the normal gut microbiome in the distal intestines. Its proteome, consisting of 4,779 members, includes a system for obtaining and breaking down dietary polysaccharides that would otherwise be difficult to digest. B. thetaiotaomicron is also an opportunistic pathogen, meaning it may become virulent in immunocompromised individuals. It is often used in research as a model organism for functional studies of the human microbiota.
Phocaeicola vulgatus,, is a mutualistic anaerobic Gram negative rod bacteria commonly found in the human gut microbiome and isolated from feces. P. vulgatus has medical relevance and has been notable in scientific research due to its production of fatty acids, potential use as a probiotic, and associations with protecting against and worsening some inflammatory diseases. Due to the difficulties in culturing anaerobic bacteria, P. vulgatus is still highly uncharacterised so efforts are being made to make use of multi-omic approaches to investigate the human gut microbiome more thoroughly in hopes to fully understand the role of this species in the development of and protection against diseases, as well as its potential uses in medicine and research. Generally, P. vulgatus is considered as a beneficial bacteria that contributes to digestion and a balanced microbiome, but it has been known to cause opportunistic infections and induce or worsen inflammatory responses. Due to its abundance in the microbiome, some researchers are investigating these species in hopes that it will be a suitable model organism for gut microbiome research, like Bacteroides thetaiotaomicron.
References
- ↑ Moncrief JS, Obiso R, Barroso LA, Kling JJ, Wright RL, Van Tassell RL, Lyerly DM, Wilkins TD (January 1995). "The enterotoxin of Bacteroides fragilis is a metalloprotease". Infection and Immunity. 63 (1): 175–81. PMC 172975 . PMID 7806355.
- ↑ Obiso RJ, Lyerly DM, Van Tassell RL, Wilkins TD (October 1995). "Proteolytic activity of the Bacteroides fragilis enterotoxin causes fluid secretion and intestinal damage in vivo". Infection and Immunity. 63 (10): 3820–6. PMC 173537 . PMID 7558286.
- ↑ Donelli G, Fabbri A, Fiorentini C (January 1996). "Bacteroides fragilis enterotoxin induces cytoskeletal changes and surface blebbing in HT-29 cells". Infection and Immunity. 64 (1): 113–9. PMC 173735 . PMID 8557328.
- ↑ Koshy SS, Montrose MH, Sears CL (December 1996). "Human intestinal epithelial cells swell and demonstrate actin rearrangement in response to the metalloprotease toxin of Bacteroides fragilis". Infection and Immunity. 64 (12): 5022–8. PMC 174483 . PMID 8945541.
- ↑ Kling JJ, Wright RL, Moncrief JS, Wilkins TD (January 1997). "Cloning and characterization of the gene for the metalloprotease enterotoxin of Bacteroides fragilis". FEMS Microbiology Letters. 146 (2): 279–84. doi: 10.1016/s0378-1097(96)00488-0 . PMID 9011050.
