in Microbiology, What is VIRULENCE PLASMIDS?

Answer 1

In a bacteria the DNA of the cell is not in a nucleus, it is in the cytoplasm. In addition some bacteria have a circular piece of DNA called a plasmid. Some plasmids can code for virulence factors and through the process of conjugation (bacterial sex using the F pili) can transfer plasmids to other bacteria and in turn make them disease causing.

Answer 2

Define Virulence

Answer 3

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This will definitely depend on the species in question. (Bacillus anthracis' main virulence factors are encoded on plasmids, not the chromosomes.) The most logical explanation for this phenomena is that the original virulence gene was regulated in a way that maximized the virulence. There may have been a promoter region near the original site of the gene. The plasmid may not have this region and therefore may not be expressed as often.

Answer 4

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in Microbiology, What is VIRULENCE PLASMIDS?

Answer 5

Plasmids Definition

Answer 6

Many pathogenic bacteria cause damage by toxins. In some cases the gene for the toxin on the chromosome. In others, the gene is on a plasmid, so non-pathogenic strains, become pathogens upon aquiring the VIRULENCE PLASMID.

Answer 7

The R-Plasmid of viruses and bacteriophages are what help them become antibacterial resistant.

Answer 8

"Virulence plasmids, which turn the bacterium into a pathogen."

http://en.wikipedia.org/wiki/Plasmid

Answer 9

Virulence is either the relative pathogenicity or the relative ability to do damage to the host of an infectious agent. The term is used mainly for viruses, but it can be more generally applied to parasites or bacteria. From an ecological point of view, virulence can be defined as the host's parasite induced loss of fitness.

Virulent bacteria
The ability of bacteria to cause disease is described in terms of the number of infecting bacteria, the route of entry into the body, the effects of host defense mechanisms, and intrinsic characteristics of the bacteria called virulence factors. Host-mediated pathogenesis is often important because the host can respond aggressively to infection with the result that host defense mechanisms do damage to host tissues while the infection is being countered.

The virulence factors of bacteria are typically proteins or other molecules that are synthesized by protein enzymes. These proteins are coded for by genes in chromosomal DNA, bacteriophage DNA or plasmids.

Types of virulence factors
* Adhesion. Many bacteria must first stick to host cells at the surface of the body. Many bacterial and host molecules that are involved in the adhesion of bacteria to host cells have been identified. Often, the host cell receptors for bacteria are essential proteins at the surface of host cells.
* Colonization factors'. Some virulent bacteria produce special proteins that allow them to colonize parts of the host body. Helicobacter pylori is able to survive in the acidic environment of the human stomach by producing the enzyme urease. Colonization of the stomach lining by this bacterium can lead to Gastric ulcer and cancer. The virulence of various strains of Helicobacter pylori tends to corellate with the level of production of urease.
* Invasion Factors. Some virulent bacteria produce proteins that either disrupt host cell membranes or stimulate endocytosis into host cells. These virulence factors allow the bacteria to enter host cells and facilitate entry into the body across epithelial tissue layers at the body surface.
* Immune response blockers. Many bacteria produce virulence factors that inhibit the host's immune system defenses. For example, a common bacterial strategy is to produce proteins that bind host antibodies.
* Toxins. Many virulence factors are proteins made by bacteria that poison host cells and cause tissue damage. For example, there are many food poisoning toxins produced by bacteria that can contaminate human foods. Some of these can remain in "spoiled" food even after cooking and cause illness when the contaminated food is consumed. Some bacterial toxins are chemically altered and inactivated by the heat of cooking.

Virulent virus
Viral virulence factors determine whether infection occurs and how severe the resulting viral disease symptoms are. Viruses often require receptor proteins on host cells to which they specifically bind. Typically, these host cell proteins are endocytosed and the bound virus then enters the host cell. Virulent viruses such as the AIDS virus (HIV) have mechanisms for evading host defenses. HIV causes a loss of T-cells and immunosuppression. Death results from opportunistic infections secondary to disruption of the immune system by the AIDS virus. Some viral virulence factors confer ability to replicate during the defensive inflammation responses of the host such as during virus-induced fever. Many viruses can exist inside a host for long periods during which little damage is done. Extremely virulent strains can eventually evolve by mutation and natural selection within the virus population inside a host.

and

A plasmid is a DNA molecule separate from the chromosomal DNA and capable of autonomous replication. It is typically circular and double-stranded. It usually occurs in bacteria, sometimes in eukaryotic organisms (e.g., the 2-micrometre-ring in Saccharomyces cerevisiae). Size of plasmids varies from 1 to over 400 kilobase pairs (kbp). There may be one copy, for large plasmids, to hundreds of copies of the same plasmid in a single cell, or even thousands of copies, for certain artificial plasmids selected for high copy number (such as the pUC series of plasmids).

The term plasmid was first introduced by the American molecular biologist Joshua Lederberg in 1952.

Types
One way of grouping plasmids is by their ability to transfer to other bacteria. Conjugative plasmids contain so-called tra-genes, which perform the complex process of conjugation, the sexual transfer of plasmids to another bacterium (Fig. 4). Non-conjugative plasmids are incapable of initiating conjugation, hence they can only be transferred with the assistance of conjugative plasmids, by 'accident'. An intermediate class of plasmids are mobilizable, and carry only a subset of the genes required for transfer. They can 'parasitise' a conjugative plasmid, transferring at high frequency only in its presence.

It is possible for plasmids of different types to coexist in a single cell. Seven different plasmids have been found in E. coli. But related plasmids are often incompatible, in the sense that only one of them survives in the cell line, due to the regulation of vital plasmid functions. Therefore, plasmids can be assigned into compatibility groups.

Another way to classify plasmids is by function. There are five main classes:
* Fertility-(F)plasmids, which contain tra-genes. They are capable of conjugation.
* Resistance-(R)plasmids, which contain genes that can build a resistance against antibiotics or poisons. Historically known as R-factors, before the nature of plasmids was understood.
* Col-plasmids, which contain genes that code for (determine the production of) colicines, proteins that can kill other bacteria.
* Degrative plasmids, which enable the digestion of unusual substances, e.g., toluene or salicylic acid.
* Virulence plasmids, which turn the bacterium into a pathogen.

Plasmids can belong to more than one of these functional groups.

Plasmids that exist only as one or a few copies in each bacterium are, upon cell division, in danger of being lost in one of the segregating bacteria. Such single-copy plasmids have systems which attempt to actively distribute a copy to both daughter cells.

Some plasmids include an addiction system or "postsegregational killing system (PSK)". They produce both a long-lived poison and a short-lived antidote. Daughter cells that retain a copy of the plasmid survive, while a daughter cell that fails to inherit the plasmid dies or suffers a reduced growth-rate because of the lingering poison from the parent cell. This is an example of plasmids as selfish DNA.

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