Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Toxic shock syndrome

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Esophageal involvement may result in difficulty in swallow-

ing, nausea, vomiting, and chest pain. Candidiasis is con-

firmed by culturefrom a swab of the infected tissue.

Proliferation of Candidais most often the result of a

weakened immune system. Candidiasis is one of the most

common and visible opportunistic infections that strike people

with AIDS, chemotherapypatients, and other immunocompro-

mised individuals. Many AIDS patients have been first diag-

nosed after they, or their dentists, noticed a thrush infection. In

individuals with normal immune systems, candidiasis may be

associated with antibiotic use. Infants, diabetics, smokers, and

denture wearers are particularly susceptible to thrush.

In addition to causing thrush, Candidamay affect the

gastrointestinal tract or genitals. The microorganism may also

enter the bloodstream, either via surgery or catheterization, or

through damage to the skin or mucosa. If the immune system

is unable to clear the fungus from the bloodstream, a danger-

ous systemic infection may occur, resulting in endocarditis,

meningitis, or other serious problems.

Antifungal medications such as fluconazole and clotri-

mazole are generally effective in treating candidiasis. However,

drug-resistant strains of Candidaare becoming increasingly

prevalent, and recurrence is common. This situation is driving

research into new therapies and potential vaccines.

See alsoBacteria and bacterial infection; Fungal genetics;

Fungi; Fungicide; Immunodeficiency; Immunosuppressant

drugs; Infection and resistance; Infection control; Microbial

flora of the oral cavity, dental caries; Yeast genetics; Yeast,

infectious

TIGR•seeTHEINSTITUTE FORGENOMICRESEARCH

(TIGR)

TMV•seeTOBACCO MOSAIC VIRUS(TMV)

TTobacco mosaic virus (TMV)OBACCO MOSAIC VIRUS(TMV)

Tobacco mosaic virus (TMV), also known as tobamovirus, is a

rod-shaped virus with ribonucleic acid(RNA) surrounded by a

coat of protein that causes mosaic-like symptoms in plants.

Mosaic-like symptoms are characterized by mottled patches of

green or yellow color on the leaves of infected plants. The virus

causes abnormal cellular function that usually does not kill the

plant but stunts growth. Infected plants may have brittle stems,

abnormally small, curled leaves, and unripened fruit.

Tobacco mosaic virus is capable of infecting many kinds

of plants, not just tobacco plants. TMV is spread through small

wounds caused by handling, insects, or broken leaf hairs that

result from leaves rubbing together. The virus attaches to the

cell wall, injects its RNA into the host cell, and forces the host

cell to produce new viral RNA and proteins. Finally, the viral

RNA and proteins assemble into new virusesand infect other

cells by passing through small openings called plasmodesmata

that connect adjacent plant cells. This process allows the virus

to take over metabolic processes without killing cells.

Tobacco mosaic virus is highly infectious and can sur-

vive for many years in dried plant parts. Currently, there is no

vaccineto protect plants from TMV, nor is there any treatment

to eliminate the virus from infected plants. However, seeds

that carry TMV externally can be treated by acid extraction or

trisodium phosphate and seeds that carry the virus internally

can receive dry heat treatments.

The discovery of viruses came about in the late 1800’s

when scientists were looking for the bacteriaresponsible for

damaging tobacco plants. During one experiment in 1892,

Russian biologist Dimitri Ivanovsky concluded that the dis-

ease in tobacco plants could not be caused by bacteria because

it passed through a fine-pored filter that is too small for bacte-

ria to pass through. In 1933, American biologist Wendell

Stanley of the Rockefeller Institute discovered that the infec-

tious agent formed crystals when purified. The purified extract

continued to cause infection when applied to healthy tobacco

plants and therefore, could not be a living organism. Soon

after, scientists were able to break down the virus into its con-

stituent parts. Today, it is known that the infectious agent that

causes the disease in tobacco plants is a virus, not bacteria.

See alsoGenetic regulation of prokaryotic cells; Plant viruses;

Viral genetics; Virus replication

TToxic shock syndromeOXIC SHOCK SYNDROME

Toxic shock syndrome is an illness caused by the bacterium

Staphylococcus aureus. The syndrome was first recognized in

the 1970s when women who were wearing a “superabsorbant”

tampon for their menstrual flow developed the illness. The

majority of cases occur with this population. Less frequently,

toxic shock syndrome can occur in females who do not use

tampons, as well as in males.

The symptoms of toxic shock syndrome are caused by a

toxin that is produced by Staphylococcus aureus. The exact

nature of the association of the bacterial growthin superab-

sorbant tampons and the production of the toxin remains

unclear. Whatever the exact cause, the cell-density behavior of

other bacterialends support to the suggestion that toxin pro-

duction is triggered by the accumulation of large numbers of

the bacteria. In the syndrome occurring in males or women

who do not use tampons, there is usually a staphylococcal

infection present in the body.

The symptoms of toxic shock syndrome include a sud-

den high fever, nausea with vomiting, diarrhea, headache,

aches all over the body, dizziness and disorientation, a sun-

burn-like rash on the palms of the hands and the soles of the

feet, and a decrease in blood pressure. The latter can send a

victim into shock and can result in death. Those who recover

may have permanent kidney and liver damage.

These symptoms are produced by the particular toxin that

is released by the bacteria. The toxin can enter the bloodstream

and move throughout the body. The toxin has been called a

“superantigen” because of its potent stimulation of cells of the

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