Bacteriophage T12 | |
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Virus classification | |
(unranked): | Virus |
Realm: | Duplodnaviria |
Kingdom: | Heunggongvirae |
Phylum: | Uroviricota |
Class: | Caudoviricetes |
Order: | Caudovirales |
Family: | Siphoviridae |
Virus: | Bacteriophage T12 |
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. [1] It converts a harmless strain of bacteria into a virulent strain. It carries the speA gene which codes for erythrogenic toxin A. [2] speA is also known as streptococcal pyogenic exotoxin A, scarlet fever toxin A, or even scarlatinal toxin. [3] [4] 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. [5] Phages with a lysogenic life cycle are also called temperate phages. [2] 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. [6] It is the main suspect as the cause of scarlet fever, an infectious disease that affects small children. [5]
The possibility of bacteriophage involvement in speA production was first introduced in 1926 when Cantacuzene and Boncieu reported that nonvirulent strains of S. pyogenes were transformed to virulent strains through some transferable element. Frobisher and Brown reported similar results in 1927, and in 1949, the reports were confirmed by Bingel [7] [8] Later, in 1964, Zabriskie reported that phage T12 could cause speA production by lysogeny in strains that it became a part of. [9] In 1980, Johnson, Schlievert and Watson were able to confirm this and show that the gene for speA production was transferred from toxigenic strains of bacteria to non-toxigenic strains through lysogeny. In their experiment, every transformed, toxin-producing bacterial colony was lysogenic, i.e. contained the T12 gene. In addition, none of the colonies containing the T12 genome was negative for speA, and therefore, the conclusion was drawn that all lysogens produced the toxin. [10] However, McKane and Ferretti reported in 1981 that a spontaneous mutant of phage T12 induced speA production virulently. This mutant, the bacteriophage T12cp1, entered the lytic cycle, a life cycle in which the host cell is destroyed. [11] In 1983, Johnson and Schlievert published a map of the T12 genome, revealing also that three rounds of packaging occur in the genome. [9] The very next year, Johnson and Schlievert and Weeks and Ferreti also found, independently, that the bacteriophage T12 carries the structural gene for speA. [8] [12] In 1986, Johnson, Tomai and Schlievert mapped the attachment site (attP) for T12 adjacent to the speA gene, and established that all bacterial strains producing the toxin carry either phage T12 itself, or a closely related bacteriophage. [5] And finally, in 1997, McShan and Ferretti published that they had found the second attachment site (attR) for T12, while also revealing in another publication, which was also credited to Tang, that bacteriophage T12 inserts into a gene that encodes a serine tRNA in the host. [2] [6]
The physical map of the T12 genome was found to be circular with a total length of 36.0kb. [9] The phage genome is reported to carry the speA gene, [12] which is a 1.7kb segment of the phage T12 genome flanked by SalI and HindIII sites. [8]
The phage integrase gene (int) and the phage attachment site (attp) are located just upstream of the speA gene in the phage genome. The bacteriophage T12 integrates into S. pyogenes chromosome by site-specific recombination into the anticodon loop of a gene that codes for serine tRNA. The bacterial attachment site (attB) has a 96 base pair sequence homologous to the phage attachment site and is located at the 3’ end of the tRNA gene such that the coding sequence of the tRNA gene remains intact after integration of the prophage. Phage T12 is the first example of a phage from a gram-positive, low G-C content host that uses this kind of integration site. [2] [6]
Diseases like scarlet fever and Streptococcal toxic shock syndrome are caused by lysogenized streptococcal strains that produce speA. The diseases are systemic responses to the speA circulating within the body. [13]
Scarlet fever, also known as scarletina, is so called because of the characteristic bright red rash it causes. It is most common in children between four and eight years of age.[ citation needed ]
The first stage of scarlet fever is typically strep throat (streptococcal pharyngitis) characterized by sore throat, fever, headache and sometimes nausea and vomiting. In two to three days, this is followed by the appearance of a diffuse erythematous rash that has a sandpaper texture. The rash first appears on the neck, then spreads to the chest, back and body extremities. A yellowish white coating covers the tongue, and is later shed, leaving the tongue with a strawberry appearance and swollen papillae. The rash fades away after five to six days of the onset of the disease, and is followed by peeling of skin, particularly over the hands and feet. [14] [15]
Penicillin, an antibiotic, is the drug of choice for the treatment of scarlet fever as for any other S. pyogenes infection. For those who are allergic to penicillin, the antibiotics erythromycin or clindamycin can be used. However, occasional resistance to these drugs has been reported. [16]
In streptococcal toxic shock syndrome (StrepTSS), speA produced by infected streptococcal strains acts as a superantigen and interacts with human monocytes and T lymphocytes, inducing T-cell proliferation and production of monokines (e.g. tumor necrosis factor α, interleukin 1, interleukin 6), and lymphokines (e.g. tumor necrosis factor β, interleukin 2, and gamma-interferon). These cytokines(TNFα, TNFβ) seem to mediate the fever, shock and organ failure characteristic of the disease. [13] [17] [18]
Strep TSS is an acute, febrile illness that begins with a mild viral-like syndrome characterized by fever, chills, myalgia, diarrhea, vomiting and nausea and involves minor soft-tissue infection that may progress to shock, multi-organ failure, and death. [18]
While penicillin is an effective treatment of mild infection, it is less effective in a severe case. Emerging treatments for strep TSS include clindamycin and intravenous gamma-globulin. [18]
The presence of lysogenic bacteriophage T12 can be tested through plaque assays if the indicator strain utilized is susceptible to the phage being tested. Plaque assays consist of pouring a soft agar solution with an indicator strain onto an agar plate. The indicator strain should be a strain of bacteria that can be infected by the phage that needs to be detected. After the soft agar is set the samples that are being tested for phage presence are then spread-plated onto the soft agar plates. The plates are then incubated overnight and checked for clearings (plaques) the next day. If the phage is present, indicator strains will become infected and go through the normal lysogenic cycle while the plates incubate, and then undergo lysis. The plaque that determines whether the phage is present or not is caused by the lysis of the indicator strains. Titers of plaques can be found by diluting the samples and counting plaque-forming units (PFUs). [19]
Biochemical tests such as Southern blots can also be used to detect the speA that the phage produces from the speA gene. This was done in research by Johnson, Tomai and Schlievert in 1985 by isolating the DNA of Streptococcal strains and running a restriction digest using BglII. After the digest was complete, the DNA samples were run on gel to separate the DNA. The DNA from this gel was then transferred to nitrocellulose paper and incubated with probes specific for speA. An image of this Southern blot can be seen in this article. [5]
Bacteriophages are very easily spread. [20] At lower exposures, Ultraviolet light can enhance the production of both phage T12 and speA. [4] Longer UV exposure times can kill the phage. UV light stresses lysogenic bacteria, leading the phages to propagate and burst the host bacterial cells. [21] In the case of T12, exposure to UV light increases the propagation of bacteriophage T12 at 20 seconds of exposure. After 20 seconds of exposure the UV light starts to kill the bacteriophage by damaging its genome. [22]
A bacteriophage, also known informally as a phage, is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν, meaning "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have structures that are either simple or elaborate. Their genomes may encode as few as four genes and as many as hundreds of genes. Phages replicate within the bacterium following the injection of their genome into its cytoplasm.
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, so as they grow, they tend to form pairs or chains that 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 enter the bloodstream an 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 (GABHS) is thus also used.
Scarlet fever, also known as Scarlatina, is an infectious disease caused by Streptococcus pyogenes a Group A streptococcus (GAS). The infection is a type of Group A streptococcal infection. It most commonly affects children between five and 15 years of age. The signs and symptoms include a sore throat, fever, headache, swollen lymph nodes, and a characteristic rash. The face is flushed and the rash is red and blanching. It typically feels like sandpaper and the tongue may be red and bumpy. The rash occurs as a result of capillary damage by exotoxins produced by S.pyogenes. On darker-pigmented skin the rash may be hard to discern.
Streptococcal pharyngitis, also known as streptococcal sore throat(strep throat), is pharyngitis (an infection of the pharynx, the back of the throat) caused by Streptococcus pyogenes, a gram-positive, group A streptococcus. Common symptoms include fever, sore throat, red tonsils, and enlarged lymph nodes in the front of the neck. A headache and nausea or vomiting may also occur. Some develop a sandpaper-like rash which is known as scarlet fever. Symptoms typically begin one to three days after exposure and last seven to ten days.
A prophage is a bacteriophage genome that is integrated into the circular bacterial chromosome or exists as an extrachromosomal plasmid within the bacterial cell. Integration of prophages into the bacterial host is the characteristic step of the lysogenic cycle of temperate phages. Prophages remain latent in the genome through multiple cell divisions until activation by an external factor, such as UV light, leading to production of new phage particles that will lyse the cell and spread. As ubiquitous mobile genetic elements, prophages play important roles in bacterial genetics and evolution, such as in the acquisition of virulence factors.
Superantigens (SAgs) are a class of antigens that result in excessive activation of the immune system. Specifically they cause non-specific activation of T-cells resulting in polyclonal T cell activation and massive cytokine release. SAgs are produced by some pathogenic viruses and bacteria most likely as a defense mechanism against the immune system. Compared to a normal antigen-induced T-cell response where 0.0001-0.001% of the body's T-cells are activated, these SAgs are capable of activating up to 20% of the body's T-cells. Furthermore, Anti-CD3 and Anti-CD28 antibodies (CD28-SuperMAB) have also shown to be highly potent superantigens.
An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines.
Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formation of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally, while the bacteriophage lies in a dormant state in the host cell. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and later events can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood. For instance the AIDS viruses can either infect humans lytically, or lay dormant (lysogenic) as part of the infected cells' genome, keeping the ability to return to lysis at a later time. The rest of this article is about lysogeny in bacterial hosts.
Diphtheria toxin is an exotoxin secreted by Corynebacterium diphtheriae, the pathogenic bacterium that causes diphtheria. The toxin gene is encoded by a prophage called corynephage β. The toxin causes the disease in humans by gaining entry into the cell cytoplasm and inhibiting protein synthesis.
Streptolysins are two hemolytic exotoxins from Streptococcus. Types include streptolysin O, which is oxygen-labile, and streptolysin S, which is oxygen-stable.
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 toxin. 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.
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.
A corynebacteriophage is a DNA-containing bacteriophage specific for bacteria of genus Corynebacterium as its host.
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.
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.
Shiranee Sriskandan is a British academic who is Professor of Infectious Diseases at Imperial College London and Honorary Consultant at Hammersmith Hospital. Her research considers how Gram-positive bacteria cause disease, with a particular focus on the bacteria Streptococcus pyogenes.
In late 2022, an ongoing disease outbreak caused by the bacterium Streptococcus pyogenes, a Lancefield group A streptococcus, began in the United Kingdom. It is often referred to as the Strep A outbreak in the media. These bacteria cause group A streptococcal infections and scarlet fever. In the UK, 260 deaths from iGAS have been recorded, of which 38 were children, 29 in England, five in Wales, three in Scotland, and one in Northern Ireland.