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Bacterial toxin[edit]

Endotoxins most commonly refer to the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) that are in the outer plasma membrane of Gram-negative bacteria.

Exotoxins are typically proteins with enzymatic activity that interfere with host cells triggering the symptoms associated with the disease. Exotoxins are also relatively specific to the bacteria that produce it; for example, diphtheria toxin is only produced by Corynebacterium diphtheriae bacteria and is required for the diphtheria disease. Not all strains of a bacteria species are virulent; there are some strains of Corynebacterium diphtheriae that do not produce diphtheria toxin and are considered nonvirulent and nontoxigenic. Additional classifications used to describe toxins include enterotoxin, neurotoxin, leukocidin or hemolysin which indicate where in the host’s body the toxin targets. Enterotoxins target the intestines, neurotoxins target neurons, leukocidin target leukocytes (white blood cells), and hemolysins target red blood cells. Exotoxin activity can be separated into specific cytotoxic activity or broad cytotoxic activity based on whether the toxin targets specific cell types or various cell types and tissues, respectively. Lethal toxins refers to the group of toxins that are the obvious agents responsible for death associated with the infection.

Bacterial toxins have been used for many years and are currently being considered for cancer therapies. Immunotoxins that originate from plants are the most widespread agents used in cancer therapy presently. Diphtheria toxin and Pseudomonas exotoxin have been extensively studied and have proven to be effective in killing cancerous cells and inhibiting or stopping protein translation. The mechanism behind this therapy involves the binding of a ligand and receptor on cancerous cells, allowing the catalytic part to kill tumor cells. Although immunotoxins have the ability to kill cancerous cells and have provided a new method of cancer treatment, they also have their obstacles. For example, immunotoxins and targeted toxins are foreign proteins, which induce the generation of neutralizing antibodies in the patient. Additionally, the specificity of the binding of the ligand and receptor to kill a tumor or cancerous cells also has the ability to destroy healthy or normal cells. Toxins that are less harmful are being used during cancer therapy to interfere with metastasis.

Clostridial toxins[edit]

Clostridial toxins are widespread and aid in the production of many diseases in humans and other organisms. Clostridial toxins are known to aid in gastrointestinal diseases and there is a wide range of mechanisms that clostridial toxins take to invade or enter the cell of the host. Pore forming bacterial toxins are common and have a very interesting way of entering or invading the host's cell. The mechanism that clostridial toxins follow includes clostridia forming pores and then the pores inserting themselves into the cell membrane of cells. Clostridial toxins have the ability to damage or alter the cell membrane damaging the extracellular matrix of the organism.

Toxin A and toxin B are two toxins produced by Clostridium difficile. Toxin A and toxin B are glycosyltransferases that cause the antibiotic-associated pseudomembranous colitis and severe diarrhea that characterize disease presentation of C. diff infections.

Botulinum neurotoxin[edit]

They also serve as powerful tools to treat an ever expanding list of medical conditions that benefit from its paralytic properties delivered through localized injections, an example drug with BoNTs as the active ingredient is Botox. Botulinum neurotoxins (BoNTs) are protein neurotoxins that are produced by the bacteria Clostridium. BoNTs are now largely being studied due to their ability to aid in chronic inflammatory diseases such as acne, multiple sclerosis, and for cosmetic purposes. There are several types of BoNT’s however, the mechanism that is used throughout all of the BoNTs are standard. This mechanism includes generalized peripheral neuroparalysis. BoNTs are now grouped or characterized based on their amino acid sequence. BoNTs amino acid sequence is extremely important to its function and toxicity. Studies have shown that there are adverse effects that BoNTs have including local diffusion leaking in the circulatory system. The initial paralysis effect is due to the local diffusion of the adjacent muscles which could potentially cause a frozen face. Overall, studies have shown that there has been a mild to moderate rate of side effects due to BoNT treatment. Long term use of BoNTs are also safe and the use of BoNTs should always be administered by a licensed medical professional.

Tetanus toxin[edit]

While tetanus toxin is produced from Clostridium tetani, a spore forming bacteria found in soil, Tetanus is a paralytic disease that is global and commonly affects newborns as well as non-immunized individuals.Tetanus enters the body of organisms through wounds or skin breaks and can be found in manure, soil, and dust. Tetanus  mechanism includes tetanus preventing the transmission of glycine and γ-aminobutyric acid from inhibitory interneurons in the spinal cord, leading to spastic paralysis. Glycine is an important amino acid that is essential for adequate nervous system function aiding in cell communication throughout the body. When tetanus toxin enters the body it is taken up by cholinergic nerve endings traveling axonally into the brain and spinal cord, disrupting motor function in individuals. Although tetanus is a damaging toxin that has a multitude of symptoms it can be prevented through vaccination.

Perfringolysin O toxin

Clostridium perfringens is an anaerobic, gram-positive bacteria that is often found in the large and small intestines of humans and other animals. Clostridium perfringens has the ability to reproduce quickly producing toxins relating to the cause of diseases. The pore-forming toxin perfringolysin has the ability to cause gangrene in calves with the presence of alpha toxin.

Staphylococcal toxins[edit]

These toxins are classified as superantigens and include staphylococcal enterotoxins which cause food-poisoning, exfoliative toxins that cause scalded skin syndrome, and toxic-shock syndrome toxin (TSST) that underlies toxic shock syndrome.

Multi-drug resistant S. aureus strains also produce alpha toxin, classified as a pore-forming toxin, which can cause abscesses.

Shiga toxins

Shiga toxins (Stxs), responsible for foodborne illnesses, are a classification of toxins produced by Stx-producing Escherichia coli (STEC) and Shigella dysenteriae serotype 1. Stx was first identified in S. dysenteriae and was later found to be produced by certain strains of E. coli. Stxs act through inhibiting protein synthesis of infected cells and can be divided into two antigenically different groups: Stx/Stx1 and Stx2. Stx1 is immunologically equivalent to Stx, however, it received a separate name to distinguish that it’s produced by STEC. Stx2 is produced only by STEC and is antigenically different from Stx/Stx1. The classification of Shiga-like toxins previously was used to refer to shiga toxins produced by E. coli, but nowadays, they are collectively referred to as shiga toxins. Within the STEC strains, a subgroup classified as enterohemorrhagic E. coli (EHEC) represent a class of pathogens that have additional virulence factors in addition to producing Stxs that result in the more severe diseases of hemorrhagic colitis and hemolytic uremic syndrome. There are around 200 strains of STEC, and the wide range of diversity between them is predominantly attributed to phage-mediated horizontal transfer of genetic material.

Anthrax toxin

Anthrax disease in humans results from infection with toxin producing Bacillus anthracis strains that can be inhaled, ingested in contaminated food or drink, or obtained through breaks in the skin like cuts or scrapes. Domestic and wild animals can also be infected via inhalation or ingestion. Depending on the route of entry, disease can present initially as inhalation anthrax, cutaneous anthrax, or gastrointestinal anthrax, but eventually will spread throughout the body, resulting in death, if not treated with antibiotics. Anthrax toxin is composed of three domains: protective antigen (PA), edema factor (EF), and lethal factor (LF). EF is an adenylate cyclase that targets ATP. LF enzyme is a metalloprotease that confers the lethal phenotype associated with anthrax disease. As LF is the agent responsible for the death of infected hosts, it is classified in the group of lethal toxins.

Diphtheria toxin

Diphtheria toxin is produced by virulent Corynebacterium diphtheriae that infect the mucosal membranes of the throat and nasal cavity causing a gray, thickened lining of the throat, sore throat, weakness, mild fever, swollen glands of the neck, and difficulty breathing. Diphtheria toxin is an ADP-ribosyltransferase that inhibits protein synthesis which causes the symptoms associated with the disease. Diphtheria used to be a leading cause of childhood death until the creation of a vaccine. The diphtheria vaccine contains a diphtheria toxoid, antigenically identical yet inactivated and non-toxic. When the toxoid is introduced to the body in a vaccine, an immune response is mounted without sequelae associated with the toxigenicity.

Pertussis toxin

Pertussis toxin is produced by virulent Bordetella pertussis and is responsible for the disease of whooping cough which can be fatal in infants. Bordetella pertussis targets cilia of the upper respiratory tract which are damaged by the Pertussis toxin, an ADP-ribosyltransferase that targets G-proteins. The severe, uncontrollable coughing makes it difficult to breathe causing the “whooping” sound that occurs with inhalation.

Cholera toxin

Cholera, characterized by copious watery diarrhea, is a potentially life-threatening illness transmitted through the fecal-oral route via food or water contaminated with toxigenic Vibrio cholerae. V. cholerae targets the intestines and secretes cholera toxin, an exotoxin and potent enterotoxin that acts as an ADP-ribosyltransferase targeting G-proteins. This causes an increase in intracellular cAMP and forces intestinal cells to expel significant amounts of water and electrolytes into the lumen.

Listeriolysin O toxin

Listeriolysin O toxin is an exotoxin produced by Listeria monocytogenes and associated with foodborne systemic illness and meningitis. Listeriolysin O toxin is classified as a pore-forming toxin that targets cholesterol cells, inserting a pore into its plasma membrane and permanently disabling cellular functioning.

Lipopolysaccharides (LPS)

Lipopolysaccharides (LPS) produced by gram-negative bacteria is an example of an endotoxin. LSP are structural components of the bacteria’s outer membrane that are rendered toxic as a result of the immune system’s destruction of the bacteria cell membrane.

Polymerase chain reaction (PCR) Real Time PCR: (https://www.frontiersin.org/articles/10.3389/fmicb.2017.00108/full) One type of PCR is real time PCR also called quantitative PCR. This type of PCR uses fluorescence and then does an analysis by measuring the amount of fluorescence that reflects the DNA sample more specifically nucleic acids at specific times. Digital PCR: (https://link.springer.com/article/10.1007/s00216-015-9107-2) Another type of PCr is digital PCR that looks at nucleic acid quantifications. Digital PCR uses diluations and samples from microlitre reactions to achieve a more accurate quantification of nucleic acids. This type offers a more linear analysis by looking at the positive and negative reactions. Digital Vs PCR Advantages: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5442518/ Both PCR’s are beneficial but there are advantages and disadvantages for both. The digital PCR has several advantages over real time PCR which includes no standard curve, more precise, less affected by simple inhibitors. Digital also has disadvantages to real time which is limited reaction mixture time, more complex and high risk of contamination. Link to PCR wiki page: https://en.wikipedia.org/wiki/Polymerase_chain_reaction

Tetrodotoxins Most of the marine life that produce this toxin are typically found in warm water for example the Red Sea and the Mediterranean Sea. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4626696/) Example: pufferfish: (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857358/) For example pufferfish do produce this toxin, some pufferfish, such as Takifugu V., produce tetrodotoxin in their skin glands.In Takifugu Vermicularis pufferfish they produce tetrodotoxin in their skin glands. Another organism that releases the tetrodotoxin from their skin are blue-ringed octopuses (Hapalochlaena fasciata) Example: Snails: (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857358/) The Natica Lineata snails produce the tetrodotoxin and store it in the muscle. The snail releases the toxin by absorbing water into the muscle cavity and it is released when the snail is attacked. Human: (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3942760/) Once a human consumes the toxin, the individual could experience mild symptoms such as paresthesias of the lips or tongue, vomiting and headaches. The individual could also experience severe symptoms such as respiratory or heart failure. At this time there is no treatment for tetrodotoxin poisoning other than respiratory support. Tetrodotoxin Wiki (https://en.wikipedia.org/wiki/Tetrodotoxin).

Detection methods in freshwater environments

The most prominent natural toxin groups that exist in aquatic environments are mycotoxins, algal toxins, bacterial toxins, and plant toxins (8). These marine biotoxins are dangerous to human health and have been widely studied due to their high potential to bioaccumulate in edible parts of seafood (8).

Autotrophic bacteria and algae are unrelated organisms; however, in aquatic environments, they are both primary producers (8). Cyanobacteria are an important autotrophic bacteria in the water food web. Explosions of cyanobacteria known as algal blooms can produce toxins harmful to both the ecosystem and human health. These harmful algal blooms are more likely to be produced at a dangerous amount when there is an excess of nutrients, the temperature is 20 degrees C, there is more light, and calmer waters (Hummert 2001). Eutrophication and other contamination can lead to an environment that promotes cyanobacteria blooms. Processes that promote an excess of nutrients, and human activities, such as agricultural runoff and sewage overflows, are primarily responsible (8). Other factors include algal species and grazers being in higher concentrations, allowing for an abundance of cyanobacterial organisms that are associated with the production of toxins (8). Detection of the extent of an algal bloom begins by taking samples of water at various depths and locations in the bloom.

Solid-phase adsorption toxin tracking (SPATT)

SPATT was introduced in 2004 as a method of monitoring aquatic toxins. This tool is able to adsorb toxins generated by microalgae or cyanobacteria, known as cyanotoxins (Roué 2018). The adsorption is passive, and the biotoxins adhere to porous, resin filled sachets, or SPATT bags where they are then physically removed and examined (MacKenzie, 2004).

SPATT is a useful tool in tracking algal blooms as it is reliable, sensitive, and inexpensive. It has the ability to quickly alert the existence of aquatic toxins which prevents it from bioaccumulating in marine life (MacKenzie, 2004). One of the downsides is that it does not give very good results for water soluble toxins as compared to hydrophobic compounds. This tool is mainly used to determine intercellular concentrations of toxins but the cyanobacteria can also be lysed to determine the total toxin amount in a sample. Other drawbacks, such as a lack in calibration and the ability to only monitor dissolved toxins, make it difficult for this tool to be implemented in a more widespread manner (Roué 2018). However, SPATT devices are able to detect many lipophilic and hydrophilic toxins that are linked to harmful algal bloom (Roué 2018).

General Background of Mycotoxins

Mycotoxins are secondary metabolites that are constructed by microfungi. Mycotoxins can be harmful because they can cause disease and death in humans and animals. They are found in many pharmaceuticals like antibiotics and growth developments (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC164220/). Mycotoxins can also play a role in chemical warfare agents, CWA, which are chemicals that contain toxins that are used to cause death, harm, or injuries to individuals that are considered enemies by the military during warfare (https://www.sciencedirect.com/science/article/pii/S1382668908000483)

Mycotoxins are synthesized by different types of moulds and are built by a wide group of toxins. Mycotoxins have a low molecular weight compound that is usually less than 1000 grams per mol. There are roughly 400 toxic mycotoxins that are constructed by 100 different fungi species that have been researched. Mycotoxins gain access into the body of a human or animal by food, they can contaminate many different types of agriculture during cultivation, harvesting, storage, and areas with high humidity. The Food and Agriculture Organization reported that about 25% of products produced by agriculture contain mycotoxins and this can lead to economic losses in the agricultural community. Levels of Mycotoxins secretion can rely on varying temperatures, the ideal temperature for Mycotoxins to grow is from 20 degrees Celsius to 37 degrees Celsius. Mycotoxin production also relies heavily on water activity, the ideal range would be from 0.83 to 0.9 aw and higher. Humidity plays a key in the production of Mycotoxins as well. The higher the humidity levels, between 70% to 90%, and moisture levels, 20% to 25%, allow the Mycotoxins to grow more rapidly. Foods that Mycotoxins are found in cereal, spices, and seeds. They can also be found in eggs, milk, and meat from animals that have been contaminated during their feeding process. Since they are resistant to high temperatures and physical and chemical reception, it is considered unavoidable while cooking at high temperatures (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7662353/).

Types of Mycotoxins

Trichothecenes is a mycotoxin that is produced from the fungi species, Fusarium graminearum. The T-2 toxin, Type A, and DON, Type B, are major mycotoxins that are responsible for toxicity in humans and animals. These two types come from an epoxide at the C12 and C13 positions in the trichothecenes. The T-2 toxin was found after civilians ate wheat that was contaminated by the Fusarium Fungi, during WWII from a biological weapon, the T-2 toxin was an outbreak and made humans develop symptoms like food poisoning, chills, nausea, dizziness, etc. The Trichothecenes mycotoxin affects animals by decreasing plasma glucose, blood cell and leukocyte counts. Pathological changes in the liver and stomach, as well as weight loss has been accounted for (https://www.frontiersin.org/articles/10.3389/fcimb.2018.00060/full).

Zearalenone is a mycotoxin that is produced from Fusarium graminearum and Fusarium culmorum that are found in different types of foods and feeds. Zearalenone is a non-steroidal estrogenic mycotoxin that is found in farm animal’s reproductive disorders and in humans it causes hypoestrogenic syndrome. Effects that come from Zearalenone include, enlarged uterus, improperly running reproductive tract, decreasing the fertility in women, and causes progesterone and estradiol levels to become not normal. If Zearalenone is consumed during pregnancy, it can cause reduced fetal weight and decrease the chance of survival for the embryo (https://www.frontiersin.org/articles/10.3389/fcimb.2018.00060/full).

Fumonisins, Fusarium verticillioides, is found in nature where fumonisin B1 has largely contaminated the area. These mycotoxins are hydrophilic compounds. Studies have shown that esophageal cancer can be related back to corn grain that contains fumonisins. Other effects from fumonisins are birth defects of the brain, spine, and spinal cord. In animals, problems with the pulmonary edema and hydrothorax swine’s have been proven to have association with fumonisins (https://www.frontiersin.org/articles/10.3389/fcimb.2018.00060/full).

Ochratoxin is a mycotoxin that is produced by Aspergillus species and Penicillium species. The most researched ochratoxin is the Ochratoxin A (OTA), which is a fungal toxin. This mycotoxin targets the OTA of kidneys and causes kidney disease in humans. Ochratoxin A is an immunosuppressive compound. Ochratoxin is a renal carcinogen, which has been found by animals containing OTA (https://www.frontiersin.org/articles/10.3389/fcimb.2018.00060/full).

Aflatoxin is a mycotoxin that is produced from Aspergillus flavus and Aspergillus parasititcus. A type of Aflatoxin, AFB1 is the most common mycotoxin that is found in human food and animal feed. AFB1 targets the liver of both humans and animals. Acute aflatoxicosis can make humans and animals have symptoms like abdominal pain, vomiting, and even death (https://www.frontiersin.org/articles/10.3389/fcimb.2018.00060/full)

Viral toxin[edit]

Rotavirus toxin NSP4

Bacteriophages

Several bacteriophages contain toxin genes that become incorporated into the host bacteria genome through infection. Many well known bacterial toxins are produced from specific strains of the bacteria species that have obtained toxigenicity through lysogenic conversion, pseudolysogeny, or horizontal gene transfer. Although these are not viral toxins, researchers remain extremely interested in the role phages play bacterial toxins due to their contribution to pathogenesis (toxigenesis), virulence, transmissibility and general evolution of bacteria.

• Cholera toxins: encoded by CTX phages, virulent Vibrio cholerae strains require lysogenic conversion by CTX phage infection
• Several botulinum toxins (BoNTs): Type C and D BoNTS have been shown to be encoded by clostridial phages and are produced by Clostridium botulinum strains harboring these phage genes
• Shiga toxins: encoded by lambdoid phages, mainly produced by lysogenic shiga-toxin producing strains of E. coli (STEC)
• Diphtheria toxins: encoded by corynephage ß, produced by lysogenic Corynebacterium diphtheriae strains infected with corynephage ß
• Several staphylococci toxins (staphylokinase (SAK), staphylococcal enterotoxin A (SEA), exfoliative toxin (ETA), Panton-Valentine leucocidin (PVL), and other enterotoxins): toxins that are phage-encoded and produced by lysogenic converted strains of the staphylococci group.

Mycoviruses

Some mycoviruses also contain toxin genes expressed by host fungal species upon viral infection. While these toxins are classified as mycotoxins, the role of mycoviruses is also of interest to researchers in terms of fungal pathogenesis. Examples include the mycoviruses ScV-M1, ScV-M2, and ScV-M28 in the Totiviridae family that contain “killer toxin” genes K1, K2, and K3, respectively. These “killer toxins” are produced by yeast, namely of the Saccharomyces cerevisiae species, that destroy neighboring yeast cells. Recently, researchers discovered that it is only the yeasts infected with either ScV-M1, ScV-M2, or ScV-M28 mycoviruses that have the ability to produce a “killer toxin.”