Glycocalyx
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[edit] Definition:
Extra cellular polymeric material produced by some bacteria. Term initially applied to the polysaccharide matrix excreted by epithelial cells forming a coating on the surface of epithelial tissue. General term for polysaccharide compounds outside the bacterial cell wall. Also called slime layer, EPS, or matrix polymer.
A glycocalyx is a network of polysaccharides that project from cellular surfaces, e.g. those of bacteria. It serves to protect the bacterium or allows the bacterium to attach itself to inert surfaces (like teeth or rocks), prokaryotes (e.g. streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony).
Its presence on inert materials (such as metal hardware implanted for fracture fixation or total joint replacement) make it difficult to eradicate deep infections as the bacteria will 'cling' on to the material via the glycocalyx. It is therefore often necessary to completely remove the hardware device in order to fully eradicate a wound infection.
The glycocalyx can be found just outside the cell wall of a bacterium. A distinct, gelatinous glycocalyx is called a capsule, while an irregular, diffuse layer is called a slime layer. Glycocalyx can help protect bacteria from phagocytes. It also helps in the formation of biofilms such as a coating on inert surfaces such as teeth or rocks.
The glycocalyx is also the name given to a specific structure of a mature platelet. The glycocalyx is unique among the cellular components of the blood. It is similar to the bacterial glycocalyx above in that it is made up of glycoproteins and allows the platelet to adhere to surfaces such as collagen of damaged vessels. The glycocalyx appears as a fluffy coat to the outer membrane of platelets and contains many of the receptor proteins that allow adhesion.
The glycocalyx is chemically unique in everyone but identical twins, and acts like an identification tag that enables the body to distinguish its own healthy cells from transplanted tissues, invading organisms and diseased cells. Human blood types and transfusion compatibility are determined by glycoproteins.
A glycocalyx can also be found on the apical portion of microvilli within the digestive tract, especially within the small intestine. It consists of glycoproteins that project from the apical plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption and includes enzymes secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars.
[edit] Functions
| Protection | Cushions the plasma membrane and protects it from physical and chemical injury. |
| Immunity To Infection | Enables the immune system to recognize and selectively attack foreign organisms. |
| Defense Against Cancer | Changes in the glycocalyx of cancerous cells enable the immune system to recognize and destroy them. |
| Transplant Compatibility | Forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplants. |
| Cell Adhesion | Binds cells together so that tissues do not fall apart. |
| Fertilization | Enables sperm to recognize and bind to eggs. |
| Embryonic Development | Guides embryonic cells to their destinations in the body. |
[edit] Pathogenesis:
After prosthesis is implanted, host defenses begin to deposit tissue onto the foreign-body surface and a layer of glycoprotein begins to develop around the artificial material. This glycoprotein film can facilitate bacterial adherence to the prosthesis. Once bacteria adhere to the surface of the prosthesis, a complex biofilm develops that surrounds the bacteria with a protective glycocalyx layer.[3] This biofilm creates a unique ecosystem on the surface of the prosthesis that allows the bacteria to adhere to the prosthesis and multiply while inhibiting the ability of antibiotics and leukocytes to penetrate to the bacteria. This glycocalyx layer may also make it difficult to recover organisms during joint aspiration and from intraoperative culture samples. Microorganisms can be introduced to prosthetic material by either contiguous spread or hematogenous dissemination. Most prosthetic joint infections probably result from contiguous spread. This may occur by direct contamination of the prosthesis during the intraoperative procedure via airborne pathogens in the operating room or from microorganisms from the skin of the patient and/or the operating room staff.[4] Trauma or the direct spread of microorganisms to the underlying prosthesis from infected overlying tissue can also result in infection. Finally, hematogenous seeding of the joint by bacterial pathogens can occur from a number of anatomic sites, including the oropharynx, respiratory tract, urinary tract, GI tract, and the skin and soft tissues.[5] It is estimated, however, that only a third of prosthetic joint infections occur through hematogenous dissemination The unique microenvironment created around the implant is primarily responsible for the difficulty in eradicating microorganisms from the site of infection. Both microbial pathogenic factors and host responses contribute to this environment, which leads to protection of the organism from clearance by host defenses and from antimicrobial access. Most microorganisms that infect prosthetic devices produce an adhesive substance called glycocalyx that adheres to the foreign material and forms a protective barrier
[edit] Treatment:
Implanted foreign materials associated with infection usually need to be removed for cure, since microbes causing infections associated with prosthetic joints, shunts, and intravenous lines produce a slime/glycocalyx on plastic/metal surfaces that permits organisms to survive despite antimicrobial therapy.
A method of inhibiting adherence of bacteria, fungus and other similar microorganisms to the surface of biomaterials is disclosed wherein biomaterials such as catheters and prosthetic devices are pretreated with a coating of a simple carbohydrate such as a mono- or disaccharide. Intravascular catheters treated as such are shown to have significant reduction of adherence by S. epidermidis, S. aureus, Candidas and other organisms associated with nosocomial infection.
cs:Glykokalyx de:Glykokalyx fr:Glycocalyx pl:Glikokaliks pt:Glicocálix tr:glikokaliks
