Microbiology and Immunology

Candidiasis WORLD OF MICROBIOLOGY AND IMMUNOLOGY

100

•

Despite the high contamination rate of foodstuffs such

as poultry, Campylobacter jejunidoes not grow readily on or

in foods. Furthermore, the organism is sensitive to tempera-

tures much above room temperature. Proper cooking of food

will readily destroy the bacteria. Other sensible hygienic prac-

tices, such as washing the cutting board after dealing with a

chicken, also reduce the chances of illness. Unfortunately,

undercooking of foods such as poultry, poor hygiene, and

inadequate disinfectionof drinking water accounts for most of

the cases of campylobacteriosis.

See alsoFood safety; Water quality

CCandidiasisANDIDIASIS

Candidiasis is an infection that is caused by members of the

fungal genus Candida.

The two most common species associated with

Candidiasis are Candida albicansand Candida glabrata. Less

commonly, but still able to cause the infection, are Candida

tropicalis, Candida parapsilosis, Candida guilliermondi, and

Candida krusei.

The fungus is a normal resident of the body, typically in

the mouth and the gastrointestinal tract. In these habitats, the

microorganism normally colonizes the cell surface. In healthy

people in the United States, Candidaspecies colonize more than

half of these individuals. The presence of the fungus is benefi-

cial. Invading bacteriaare recognized by the Candidacells and

are destroyed. Thus, the fungi complementthe immune system

and other defenses of the body against infection.

When the body is in proper balance with respect to the

microbial flora, the fungi exist as a so-called yeastform.

These are not capable of invasion. However, Candidacan

infect areas of the body that are warm and moist. These

include the eye (conjunctivitis), fingernails, rectum, folds in

the skin, and, in infants, the skin irritation in infants known

commonly as diaper rash. Typically, such infections are more

of an inconvenience than a dangerous health concern.

However, in people whose immune systems are com-

promised in some way, or when the normal balance of the

microbial flora has been disrupted by, for example, antibiotic

therapy, Candidacan establish an infection. For example, an

infection of the mouth region, which is referred to as oropha-

ryngeal infection, was a very common infection in those

whose immune system was deficient due to infection with the

Human immunodeficiency virus. More aggressive antiviral

therapy has reduced the incidence of the infection.

Such infections are associated with the change from the

Candidacells from the yeast form to a so-called mycelial fun-

gal form. The mycelia produce long, root-like structures that

are called rhizoids. The rhizoids can penetrate through the

mucous cells that line the inside of the mouth and vagina, and

through the epithelial cells that line the intestinal tract. This

invasion can spread the infection to the bloodstream. As well,

the microscopic holes that are left behind in the cell walls can

be portals for the entry of toxins, undigested food, bacteria,

and yeast.

In countries around the world where fungal infections

are widespread in the populations, Candidaspecies have over-

taken Cryptococcusspecies as the most common cause of

infections that affect the central nervous system of immuno-

compromised people.

Besides the oropharyngeal infection, Candidacan also

commonly cause a vaginal infection. Both infections are evi-

dent by the development of a fever and chills that, because of

the fungal genesis of the infections, are unaffected by antibac-

terial therapy. Visually, white patches appear on the surface of

the cells lining the mouth and oral cavity and the vagina. More

rarely, the infections may spread to the bloodstream.

Examples of the infections that can result include the kidney,

spleen, nerve cells (meningitis), heart (endocarditis). Arthritis

may even develop. Immunocompromised individuals are

especially susceptible to these infections.

The contamination of the bloodstream by Candida

occurs most commonly in the hospital setting, where a patient

is being treated for Candidiasis or other malady. Indeed, this

type of bloodstream infection is the fourth most common

cause of hospital-acquired bloodstream infections in the

United States. The death rate from the infection can approach

40 per cent.

Treatment for Candidainfections consist of the admin-

istration of antifungal drugs. Examples of the drugs of choice

include amphotericin B, fluconazole, ketoconazole, and ny-

statin. The real possibility of the development of irritative side

effects makes monitoring during therapy a prudent precaution.

See alsoFungi; Immunodeficiency

CAPSID AND CAPSULE•seeGLYCOCALYX

CCarbon cycle in microorganismsARBON CYCLE IN MICROORGANISMS

The carbon cycle in microorganismsis part of a larger cycling

of carbon that occurs on the global scale. The actions of

microorganisms help extract carbon from non-living sources

and make the carbon available to living organisms (including

themselves).

The cycling of carbon by microorganisms, including a

variety of bacteriaand fungi, occurs in aquatic habitats. Even

relatively oxygen-free zones such as in the deep mud of lakes,

ponds and other water bodies can be regions where the anaer-

obic conversion of carbon takes place.

Much of the carbon that enters the carbon cycle of

microorganisms is carbon dioxide. This form of carbon exists

as a gas in the atmosphere and can be dissolved in water. The

atmospheric carbon dioxide can be converted to organic mate-

rial in the process of photosynthesis. Photosynthetic algae are

important microorganisms in this regard. As well, chemoau-

totrophs, primarily bacteria and archae are capable of carbon

dioxide conversion. In both systems the carbon dioxide is

converted to chains that are comprised of sugars that have the

structure CH 2 O.

womi_C 5/6/03 2:04 PM Page 100