Yersinia pseudotuberculosis
Yersinia pseudotuberculosis is a Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 bacterium that causes Pseudotuberculosis (Yersinia) disease in animals; humans occasionally get infected zoonotically
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...

, most often through the food-borne route.


In animals, Y. pseudotuberculosis can cause tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

-like symptoms, including localized tissue necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...

 and granulomas in the spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

, liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, and lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...


In humans, symptoms of Pseudotuberculosis (Yersinia) are similar to those of infection with Yersinia enterocolitica
Yersinia enterocolitica
Yersinia enterocolitica is a species of gram-negative coccobacillus-shaped bacterium, belonging to the family Enterobacteriaceae. Yersinia enterocolitica infection causes the disease yersiniosis, which is a zoonotic disease occurring in humans as well as a wide array of animals such as cattle,...

(fever and right-sided abdominal pain), except that the diarrheal component is often absent, which sometimes makes the resulting condition difficult to diagnose. Y. pseudotuberculosis infections can mimic appendicitis
Appendicitis is a condition characterized by inflammation of the appendix. It is classified as a medical emergency and many cases require removal of the inflamed appendix, either by laparotomy or laparoscopy. Untreated, mortality is high, mainly because of the risk of rupture leading to...

, especially in children and younger adults, and, in rare cases, the disease may cause skin complaints (erythema nodosum
Erythema nodosum
Erythema nodosum is an inflammation of the fat cells under the skin characterized by tender red nodules or lumps that are usually seen on both shins...

), joint stiffness and pain (reactive arthritis
Reactive arthritis
Reactive arthritis , is classified as an autoimmune condition that develops in response to an infection in another part of the body. Coming into contact with bacteria and developing an infection can trigger the disease. Reiter's syndrome has symptoms similar to various other conditions collectively...

), or spread of bacteria to the blood (bacteremia
Bacteremia is the presence of bacteria in the blood. The blood is normally a sterile environment, so the detection of bacteria in the blood is always abnormal....


Pseudotuberculosis (Yersinia) usually becomes apparent 5–10 days after exposure and typically lasts 1–3 weeks without treatment. In complex cases or those involving immunocompromised patients, antibiotics may be necessary for resolution; ampicillin
Ampicillin is a beta-lactam antibiotic that has been used extensively to treat bacterial infections since 1961. Until the introduction of ampicillin by the British company Beecham, penicillin therapies had only been effective against Gram-positive organisms such as staphylococci and streptococci...

, aminoglycosides, tetracycline, chloramphenicol
Chloramphenicol is a bacteriostatic antimicrobial that became available in 1949. It is considered a prototypical broad-spectrum antibiotic, alongside the tetracyclines, and as it is both cheap and easy to manufacture it is frequently found as a drug of choice in the third world.Chloramphenicol is...

, or a cephalosporin
The cephalosporins are a class of β-lactam antibiotics originally derived from Acremonium, which was previously known as "Cephalosporium".Together with cephamycins they constitute a subgroup of β-lactam antibiotics called cephems.-Medical use:...

 may all be effective.

The recently described syndrome Izumi-fever has been linked to infection with Y.pseudotuberculosis.

The symptoms of fever and abdominal pain mimicking appendicitis
Appendicitis is a condition characterized by inflammation of the appendix. It is classified as a medical emergency and many cases require removal of the inflamed appendix, either by laparotomy or laparoscopy. Untreated, mortality is high, mainly because of the risk of rupture leading to...

 (actually from mesenteric lymphadenitis) associated with Y. pseudotuberculosis infection are not typical of the diarrhea and vomiting from classical food poisoning incidents. Although Y. pseudotuberculosis is usually only able to colonize hosts by peripheral routes and cause serious disease in immunocompromised individuals, if this bacterium gains access to the blood stream, it has an LD50 comparable to Y. pestis at only 10CFU.

Virulence Factors

To facilitate attachment, invasion, and colonization of its host, this bacterium possesses many virulence factors. Superantigens, bacterial adhesions, and the actions of Yops (which are bacterial proteins once thought to be "Yersinia outer membrane proteins") that are encoded on the "[plasmid] for Yersinia virulence" – commonly known as the pYV – cause host pathogenesis and allow the bacteria to live parasitically.


The 70kb pYV is critical to Yersiniae pathogenicity, since it contains many genes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

 known to encode virulence factors and its loss gives avirulence of all Yersiniae. A 26kb "core region" in the pYV contains the ysc genes, which regulate the expression and secretion of Yops. Many Ysc proteins also amalgamate to form a type III secretory apparatus, which secretes many Yops into the host cell cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 with the assistance of the "translocation apparatus", constructed of YopB and YopD. The core region also includes yopN, yopB, yopD, tyeA, lcrG, and lcrV, which also regulate Yop gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 and help to translocate secretory Yops to the target cell. For example, YopN and TyeA are positioned as a plug on the apparatus so that only their conformational change, induced by their interaction with certain host cell membrane proteins, will cause the unblocking of the secretory pathway. Secretion is regulated in this fashion so that proteins are not expelled into the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...

 and elicit an immune response. Since this pathway gives secretion selectivity, it is a virulence factor.

Effector Yops

In contrast to the ysc and yop genes listed above, the Yops that act directly on host cells to cause cytopathologic effects – "effector Yops" – are encoded by pYV genes external to this core region. The sole exception is LcrV, which is also known as the "versatile Yop" for its two roles as an effector Yop and as a regulatory Yop. The combined function of these effector Yops permits the bacteria to resist internalization by immune and intestinal cells and to evade the bactericidal actions of neutrophils and macrophages. Inside the bacterium, these Yops are bound by pYV-encoded Sycs (specific Yop chaperones), which prevent premature interaction with other proteins and guide the Yops to a type III secretory apparatus. In addition to the Syc-Yop complex, Yops are also tagged for type III secretion either by the first 60nt in their corresponding mRNA transcript or by their corresponding first 20 N-terminal amino acids.
LcrV, YopQ, YopE, YopT, YopH, YpkA, YopJ, YopM, and YadA are all secreted by the type III secretory pathway. LcrV inhibits neutrophil chemotaxis
Chemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules,...

 and cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...

 production, allowing Y. Pseudotuberculosis to form large colonies without inducing systemic failure and, with YopQ, contributes to the translocation process by bringing YopB and YopD to the eukaryotic cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 for pore-formation. By causing actin filament depolymerisation, YopE, YopT, and YpkA resist endocytosis
Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...

 by intestinal cells and phagocytosis while giving cytotoxic changes in the host cell. YopT targets Rho GTPase, commonly named "RhoA", and uncouples it from the membrane, leaving it in an inactive RhoA-GDI (guanine nucleotide dissociation inhibitor)-bound state whereas YopE and YpkA convert Rho proteins to their inactive GDP-bound states by expressing GTPase activity. YpkA also catalyses serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...

 autophosporylation, so it may have regulatory functions in Yersinia or undermine host cell immune response signal cascades since YpkA is targeted to the cytoplasmic side of the host cell membrane. YopH acts on host focal adhesion sites by dephosphorylating several phosphotyrosine residues on focal adhesion kinase (FAK) and the focal adhesion proteins paxillin
Paxillin is a signal transduction adaptor protein discovered in 1990 in the laboratory of Keith Burridge and should not be confused with the neurotoxin paxilline. The C-terminal region of paxillin contains four LIM domains that target paxillin to focal adhesions, it is presumed through a direct...

 and p130. Since FAK phosphorylation is involved in uptake of yersiniae as well as T cell
T cell
T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...

 and B cell
B cell
B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

 responses to antigen-binding, YopH elicits antiphagocytic and other anti-immune effects. YopJ, which shares an operon
In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create...

 with YpkA, "...interferes with the mitogen-activated protein (MAP) kinase activities of c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase", leading to macrophage apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

. In addition, YopJ inhibits TNF-α release from many cell types, possibly through an inhibitory action on NF-κB, suppressing inflammation and the immune response. By secretion through a type III pathway and localization in the nucleus by a vesicle-associated, microtubule-dependent method, YopM may alter host cell growth by binding to RSK (ribosomal S6 kinase), which regulates cell cycle regulation genes. Interestingly, YadA has lost its adhesion, opsonisation-resisting, phagocytosis-resisting, and respiratory burst
Respiratory burst
Respiratory burst is the rapid release of reactive oxygen species from different types of cells....

-resisting functions in Y. pseudotuberculosis due to a frameshift mutation
Frameshift mutation
A frameshift mutation is a genetic mutation caused by indels of a number of nucleotides that is not evenly divisible by three from a DNA sequence...

 by a single base-pair deletion in yadA in comparison to yadA in Y. enterocolitica, yet it still is secreted by type III secretion. The yop genes, yadA, ylpA, and the virC operon are considered the "Yop regulon" since they are coregulated by pYV-encoded VirF. virF is in turn thermoregulated. At 37 degrees Celsius, chromosomally-encoded Ymo, which regulates DNA supercoiling around the virF gene, changes conformation, allowing for VirF expression, which then up-regulates the Yop regulon.


Y. pseudotuberculosis adheres strongly to intestinal cells via chromosomally encoded proteins so that Yop secretion may occur, to avoid being removed by peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

, and to invade target host cells. A transmembrane protein, Invasin, facilitates these functions by binding to host cell αβ1 integrins. Through this binding, the integrins cluster, thereby activating FAK, and causing a corresponding reorganization of the cytoskeleton. Subsequent internalization of bound bacteria occurs when the actin-depolymerising Yops are not being expressed. The protein encoded on the "attachment invasion locus" named Ail also bestows attachment and invasive abilities upon Yersiniae while interfering with the binding of complement on the bacterial surface. To increase binding specificity, the fibrillar pH6 antigen targets bacteria to target intestinal cells only when thermoinduced.


Certain strains of Yersinia pseudotuberculosis express a superantigenic exotoxin, YPM, or the Y. pseudotuberculosis-derived mitogen, from the chromosomal ypm gene. YPM specifically binds and causes the proliferation of T lymphocytes expressing the Vβ3, Vβ7, Vβ8, Vβ9, Vβ13.1, and Vβ13.2 variable regions with CD4+ T cell preference, although activation of some CD8+ T cell
T cell
T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...

s occurs. This T cell expansion can cause splenomegaly
Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant of the human abdomen. It is one of the four cardinal signs of hypersplenism, some reduction in the number of circulating blood cells affecting granulocytes, erythrocytes or platelets in any...

 coupled with IL-2 and IL-4 overproduction. Since administering anti-TNF-α and anti-IFN-γ monoclonal antibodies neutralizes YPM toxicity in vivo, these cytokines are largely responsible for the damage caused indirectly by the exotoxin
An exotoxin is a toxin excreted by a microorganism, like bacteria, fungi, algae, and protozoa. 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...

. Strains that carry the exotoxin gene are rare in Western countries, where the disease, when at all apparent, manifests itself largely with minor symptoms, whereas more than 95% of strains from Far Eastern countries contain ypm and are correlated with Izumi fever and Kawasaki disease
Kawasaki disease
Kawasaki disease , also known as Kawasaki syndrome, lymph node syndrome and mucocutaneous lymph node syndrome, is an autoimmune disease in which the medium-sized blood vessels throughout the body become inflamed. It is largely seen in children under five years of age...

Although the superantigen poses the greatest threat to host health, all virulence factors contribute to Y. pseudotuberculosis viability in vivo and define the bacterium’s pathogenic characteristics. Y. pseudotuberculosis can live extracellularly due to its formidable mechanisms of phagocytosis and opsonisation resistance through the expression of Yops and the type III pathway; yet, by limited pYV action, it can populate host cells, especially macrophages, intracellularly to further evade immune responses and be disseminated throughout the body.

External links

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