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Streptococcus is a genus of gram-positive coccus or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales, in the phylum Bacillota. Cell division in streptococci occurs along a single axis, thus when growing they tend to form pairs or chains, which may appear bent or twisted. This differs from staphylococci, which divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Most streptococci are oxidase-negative and catalase-negative, and many are facultative anaerobes.
Group A streptococcal infections are a number of infections with Streptococcus pyogenes, a group A streptococcus (GAS). S. pyogenes is a species of beta-hemolytic Gram-positive bacteria that is responsible for a wide range of infections that are mostly common and fairly mild. If the bacteria enters the bloodstream, the infection can become severe and life-threatening, and is called an invasive GAS (iGAS).
Streptococcus pyogenes is a species of Gram-positive, aerotolerant bacteria in the genus Streptococcus. These bacteria are extracellular, and made up of non-motile and non-sporing cocci that tend to link in chains. They are clinically important for humans, as they are an infrequent, but usually pathogenic, part of the skin microbiota that can cause Group A streptococcal infection. S. pyogenes is the predominant species harboring the Lancefield group A antigen, and is often called group A Streptococcus (GAS). However, both Streptococcus dysgalactiae and the Streptococcus anginosus group can possess group A antigen as well. Group A streptococci, when grown on blood agar, typically produce small (2–3 mm) zones of beta-hemolysis, a complete destruction of red blood cells. The name group A (beta-hemolytic) Streptococcus is thus also used.
Rheumatic fever (RF) is an inflammatory disease that can involve the heart, joints, skin, and brain. The disease typically develops two to four weeks after a streptococcal throat infection. Signs and symptoms include fever, multiple painful joints, involuntary muscle movements, and occasionally a characteristic non-itchy rash known as erythema marginatum. The heart is involved in about half of the cases. Damage to the heart valves, known as rheumatic heart disease (RHD), usually occurs after repeated attacks but can sometimes occur after one. The damaged valves may result in heart failure, atrial fibrillation and infection of the valves.
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.
Hemolysis is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms. This is particularly useful in classifying streptococcal species. A substance that causes hemolysis is called a hemolysin.
Virulence factors are cellular structures, molecules and regulatory systems that enable microbial pathogens to achieve the following:
Adenylate cyclase toxin is a virulence factor produced by some members of the genus Bordetella. Together with the pertussis toxin it is the most important virulence factor of the causative agent of whooping cough, Bordetella pertussis. Bordetella bronchiseptica and Bordetella parapertussis, also able to cause pertussis-like symptoms, also produce adenylate cyclase toxin. It is a toxin secreted by the bacteria to influence the host immune system.
Cytolysin refers to the substance secreted by microorganisms, plants or animals that is specifically toxic to individual cells, in many cases causing their dissolution through lysis. Cytolysins that have a specific action for certain cells are named accordingly. For instance, the cytolysins responsible for the destruction of red blood cells, thereby liberating hemoglobins, are named hemolysins, and so on. Cytolysins may be involved in immunity as well as in venoms.
Hemolysins or haemolysins are lipids and proteins that cause lysis of red blood cells by disrupting the cell membrane. Although the lytic activity of some microbe-derived hemolysins on red blood cells may be of great importance for nutrient acquisition, many hemolysins produced by pathogens do not cause significant destruction of red blood cells during infection. However, hemolysins are often capable of lysing red blood cells in vitro.
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.
Anti-streptolysin O is the antibody made against streptolysin O, an immunogenic, oxygen-labile streptococcal hemolytic exotoxin produced by most strains of group A and many strains of groups C and G Streptococcus bacteria. The "O" in the name stands for oxygen-labile; the other related toxin being oxygen-stable streptolysin-S. The main function of streptolysin O is to cause hemolysis —in particular, beta-hemolysis.
M protein is a virulence factor that can be produced by certain species of Streptococcus.
Streptococcus dysgalactiae is a gram positive, beta-haemolytic, coccal bacterium belonging to the family Streptococcaceae. It is capable of infecting both humans and animals, but is most frequently encountered as a commensal of the alimentary tract, genital tract, or less commonly, as a part of the skin flora. The clinical manifestations in human disease range from superficial skin-infections and tonsillitis, to severe necrotising fasciitis and bacteraemia. The incidence of invasive disease has been reported to be rising. Several different animal species are susceptible to infection by S. dysgalactiae, but bovine mastitis and infectious arthritis in lambs have been most frequently reported.
Perianal cellulitis, also known as perianitis or perianal streptococcal dermatitis, is a bacterial infection affecting the lower layers of the skin (cellulitis) around the anus. It presents as bright redness in the skin and can be accompanied by pain, difficulty defecating, itching, and bleeding. This disease is considered a complicated skin and soft tissue infection (cSSTI) because of the involvement of the deeper soft tissues.
Streptococcal pyrogenic exotoxins also known as erythrogenic toxins, are exotoxins secreted by strains of the bacterial species Streptococcus pyogenes. SpeA and speC are superantigens, which induce inflammation by nonspecifically activating T cells and stimulating the production of inflammatory cytokines. SpeB, the most abundant streptococcal extracellular protein, is a cysteine protease. Pyrogenic exotoxins are implicated as the causative agent of scarlet fever and streptococcal toxic shock syndrome. There is no consensus on the exact number of pyrogenic exotoxins. Serotypes A-C are the most extensively studied and recognized by all sources, but others note up to thirteen distinct types, categorizing speF through speM as additional superantigens. Erythrogenic toxins are known to damage the plasma membranes of blood capillaries under the skin and produce a red skin rash. Past studies have shown that multiple variants of erythrogenic toxins may be produced, depending on the strain of S. pyogenes in question. Some strains may not produce a detectable toxin at all. Bacteriophage T12 infection of S. pyogenes enables the production of speA, and increases virulence.
The thiol-activated Cholesterol-dependent Cytolysin(CDC) family is a member of the MACPF superfamily. Cholesterol dependent cytolysins are a family of β-barrel pore-forming exotoxins that are secreted by gram-positive bacteria. CDCs are secreted as water-soluble monomers of 50-70 kDa, that when bound to the target cell, form a circular homo-oligomeric complex containing as many as 40 monomers. Through multiple conformational changes, the β-barrel transmembrane structure is formed and inserted into the target cell membrane. The presence of cholesterol in the target membrane is required for pore formation, though the presence of cholesterol is not required by all CDCs for binding. For example, intermedilysin secreted by Streptococcus intermedius will bind only to target membranes containing a specific protein receptor, independent of the presence of cholesterol, but cholesterol is required by intermedilysin for pore formation. While the lipid environment of cholesterol in the membrane can affect toxin binding, the exact molecular mechanism that cholesterol regulates the cytolytic activity of the CDC is not fully understood.
Bacteriophage T12 is a bacteriophage that infects Streptococcus pyogenes bacteria. It is a proposed species of the family Siphoviridae in the order Caudovirales also known as tailed viruses. It converts a harmless strain of bacteria into a virulent strain. It carries the speA gene which codes for erythrogenic toxin A. speA is also known as streptococcal pyogenic exotoxin A, scarlet fever toxin A, or even scarlatinal toxin. Note that the name of the gene "speA" is italicized; the name of the toxin "speA" is not italicized. Erythrogenic toxin A converts a harmless, non-virulent strain of Streptococcus pyogenes to a virulent strain through lysogeny, a life cycle which is characterized by the ability of the genome to become a part of the host cell and be stably maintained there for generations. Phages with a lysogenic life cycle are also called temperate phages. Bacteriophage T12, proposed member of family Siphoviridae including related speA-carrying bacteriophages, is also a prototypic phage for all the speA-carrying phages of Streptococcus pyogenes, meaning that its genome is the prototype for the genomes of all such phages of S. pyogenes. It is the main suspect as the cause of scarlet fever, an infectious disease that affects small children.
RopB transcriptional regulator, also known as RopB/Rgg transcriptional regulator is a transcriptional regulator protein that regulates expression of the extracellularly secreted cysteine protease streptococcal pyrogenic exotoxin B (speB) [See Also: erythrogenic toxins] which is an important virulence factor of Streptococcus pyogenes and is responsible for the dissemination of a host of infectious diseases including strep throat, impetigo, streptococcal toxic shock syndrome, necrotizing fasciitis, and scarlet fever. Functional studies suggest that the ropB multigene regulon is responsible for not only global regulation of virulence but also a wide range of functions from stress response, metabolic function, and two-component signaling. Structural studies implicate ropB's regulatory action being reliant on a complex interaction involving quorum sensing with the leaderless peptide signal speB-inducing peptide (SIP) acting in conjunction with a pH sensitive histidine switch.
Streptococcosis is an infectious disease caused by bacteria of the genus Steptococcus. This disease is most common among horses, guinea pigs, dogs, cats, and fish with symptoms varying based on the streptococcal species involved. In humans, this disease typically involves a throat infection and is called streptococcal pharyngitis or strep throat.
References
- ↑ "streptolysin" at Dorland's Medical Dictionary
- ↑ Streptolysin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- ↑ Sierig G, Cywes C, Wessels MR, Ashbaugh CD (January 2003). "Cytotoxic effects of streptolysin o and streptolysin s enhance the virulence of poorly encapsulated group a streptococci". Infection and Immunity. 71 (1): 446–55. doi:10.1128/IAI.71.1.446-455.2003. PMC 143243 . PMID 12496195.
- ↑ Billington SJ, Jost BH, Songer JG (January 2000). "Thiol-activated cytolysins: structure, function and role in pathogenesis". FEMS Microbiology Letters. 182 (2): 197–205. doi: 10.1111/j.1574-6968.2000.tb08895.x . PMID 10620666.
- ↑ Lee SW, Mitchell DA, Markley AL, Hensler ME, Gonzalez D, Wohlrab A, et al. (April 2008). "Discovery of a widely distributed toxin biosynthetic gene cluster". Proceedings of the National Academy of Sciences of the United States of America. 105 (15): 5879–84. doi: 10.1073/pnas.0801338105 . PMC 2311365 . PMID 18375757.
- ↑ Abdel Ghani EM, Weis S, Walev I, Kehoe M, Bhakdi S, Palmer M (November 1999). "Streptolysin O: inhibition of the conformational change during membrane binding of the monomer prevents oligomerization and pore formation". Biochemistry. 38 (46): 15204–11. doi:10.1021/bi991678y. PMID 10563803.
- ↑ Vita GM, De Simone G, Leboffe L, Montagnani F, Mariotti D, Di Bella S, et al. (2020-12-08). "Human Serum Albumin Binds Streptolysin O (SLO) Toxin Produced by Group A Streptococcus and Inhibits Its Cytotoxic and Hemolytic Effects". Frontiers in Immunology. 11: 507092. doi: 10.3389/fimmu.2020.507092 . PMC 7752801 . PMID 33363530.
- ↑ Reglinski M, Sriskandan S (2015). "Streptococcus pyogenes". Molecular Medical Microbiology. Elsevier. pp. 675–716. doi:10.1016/b978-0-12-397169-2.00038-x. ISBN 978-0-12-397169-2.
- ↑ Weckel A, Guilbert T, Lambert C, Plainvert C, Goffinet F, Poyart C, et al. (February 2021). "Streptococcus pyogenes infects human endometrium by limiting the innate immune response". The Journal of Clinical Investigation. 131 (4). bioRxiv 10.1101/713875 . doi:10.1172/jci130746. PMC 7880408 . PMID 33320843.
- ↑ Maxson T, Deane CD, Molloy EM, Cox CL, Markley AL, Lee SW, Mitchell DA (May 2015). "HIV protease inhibitors block streptolysin S production". ACS Chemical Biology. 10 (5): 1217–26. doi:10.1021/cb500843r. PMC 4574628 . PMID 25668590.
- ↑ Molloy EM, Cotter PD, Hill C, Mitchell DA, Ross RP (August 2011). "Streptolysin S-like virulence factors: the continuing sagA". Nature Reviews. Microbiology. 9 (9): 670–81. doi:10.1038/nrmicro2624. PMC 3928602 . PMID 21822292.
