Virulence is a pathogen's or microorganism's ability to cause damage to a host.
Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by covalent bonds, and are found in the bacterial capsule, the outermost membrane of cell envelope of Gram-negative bacteria, such as E. coli and Salmonella. Today, the term endotoxin is often used synonymously with LPS, although there are a few endotoxins that are not related to LPS, such as the so-called delta endotoxin proteins produced by Bacillus thuringiensis.
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.
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mechanism of cell secretion is via secretory portals at the plasma membrane called porosomes. Porosomes are permanent cup-shaped lipoprotein structures embedded in the cell membrane, where secretory vesicles transiently dock and fuse to release intra-vesicular contents from the cell.
Pathogenicity islands (PAIs), as termed in 1990, are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. Pathogenicity islands are found in both animal and plant pathogens. Additionally, PAIs are found in both gram-positive and gram-negative bacteria. They are transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon. Therefore, PAIs contribute to microorganisms' ability to evolve.
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.
Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually in the host they are infecting or living in. Adhesins are a type of virulence factor.
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.
Yersinia pseudotuberculosis is a Gram-negative bacterium that causes Far East scarlet-like fever in humans, who occasionally get infected zoonotically, most often through the food-borne route. Animals are also infected by Y. pseudotuberculosis. The bacterium is urease positive.
Host tropism is the infection specificity of certain pathogens to particular hosts and host tissues. This explains why most pathogens are only capable of infecting a limited range of host organisms.
Xanthomonas campestris is a gram-negative, obligate aerobic bacterium that is a member of the Xanthomonas genus, which is a group of bacteria that are commonly known for their association with plant disease. This species includes Xanthomonas campestris pv. campestris the cause of black rot of brassicas, one of the most important diseases of brasicas worldwide.
Intimin is a virulence factor (adhesin) of EPEC and EHEC E. coli strains. It is an attaching and effacing (A/E) protein, which with other virulence factors is necessary and responsible for enteropathogenic and enterohaemorrhagic diarrhoea.
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.
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.
The AB toxins are two-component protein complexes secreted by a number of pathogenic bacteria, though there is a pore-forming AB toxin found in the eggs of a snail. They can be classified as Type III toxins because they interfere with internal cell function. They are named AB toxins due to their components: the "A" component is usually the "active" portion, and the "B" component is usually the "binding" portion. The "A" subunit possesses enzyme activity, and is transferred to the host cell following a conformational change in the membrane-bound transport "B" subunit. These proteins consist of two independent polypeptides, which correspond to the A/B subunit moieties. The enzyme component (A) enters the cell through endosomes produced by the oligomeric binding/translocation protein (B), and prevents actin polymerisation through ADP-ribosylation of monomeric G-actin.
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.
Pathogenomics is a field which uses high-throughput screening technology and bioinformatics to study encoded microbe resistance, as well as virulence factors (VFs), which enable a microorganism to infect a host and possibly cause disease. This includes studying genomes of pathogens which cannot be cultured outside of a host. In the past, researchers and medical professionals found it difficult to study and understand pathogenic traits of infectious organisms. With newer technology, pathogen genomes can be identified and sequenced in a much shorter time and at a lower cost, thus improving the ability to diagnose, treat, and even predict and prevent pathogenic infections and disease. It has also allowed researchers to better understand genome evolution events - gene loss, gain, duplication, rearrangement - and how those events impact pathogen resistance and ability to cause disease. This influx of information has created a need for bioinformatics tools and databases to analyze and make the vast amounts of data accessible to researchers, and it has raised ethical questions about the wisdom of reconstructing previously extinct and deadly pathogens in order to better understand virulence.
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.
Omptins are a family of bacterial proteases. They are aspartate proteases, which cleave peptides with the use of a water molecule. Found in the outer membrane of gram-negative enterobacteria such as Shigella flexneri, Yersinia pestis, Escherichia coli, and Salmonella enterica. Omptins consist of a widely conserved beta barrel spanning the membrane with 5 extracellular loops. These loops are responsible for the various substrate specificities. These proteases rely upon binding of lipopolysaccharide for activity.
Antivirulence is the concept of blocking virulence factors. In regards to bacteria, the idea is to design agents that block virulence rather than kill bacteria en masse, as the current regime results in much more selective pressure.
