FUNGI

INTRODUCTION: Fungi may be unicellular, such as yeasts, or multicellular, such as the familiar molds and mushrooms. Most fungi are saprophytes; that is, they live on dead organic matter and decompose it to recycle the chemicals as nutrients. The pathogenic fungi cause infections that are called mycoses (singular: mycosis), which may be superficial or systemic.

YEASTS: Yeasts have been used by people for thousands of years in baking and brewing. In small numbers, yeasts such as Candida albicans are part of the resident flora of the skin, mouth, intestines, and vagina. Normal flora

In larger numbers, however, yeasts may cause superficial infections of mucous membranes or the skin, or very serious systemic infections of internal organs. An all-too-common trigger for oral or vaginal yeast infections is the use of an antibiotic to treat a bacterial infection. Antibiotics

The antibiotic diminishes the normal bacterial flora, thereby removing competition for the yeasts, which are then able to overgrow. Yeasts may also cause skin infections in diabetics, or in obese people who have skin folds that are always moist. Diabetes mellitus: Obesity

NOSOCOMIAL FUNGAL INFECTIONS: In recent years, Candida has become an important cause of nosocomial infections. The resistance of hospital patients is often lowered because of their diseases or treatments, and they are more susceptible to systemic yeast infections in the form of pneumonia or endocarditis. Pneumonia

Another superficial mycosis is ringworm (tinea), which may be caused by several species of fungi. The name ringworm is misleading, because there are no worms involved. It is believed to have come from the appearance of the lesions: circular, scaly patches with red dened edges; the center clears as the lesion grows. Athlete’s foot, which is probably a bacterial-fungal infection, is perhaps the most common form of ringworm.

SYSTEMIC MYCOSES: The systemic mycoses are more serious diseases that occur when spores of some fungi gain access to the interior of the body. Most of these fungi grow in a mold-like pattern. The molds we sometimes see on stale bread or overripe fruit look fluffy or fuzzy. The fluff is called a mycelium and is made of many threadlike cellular structures called hyphae. The color of a mold is due to the spore cases (sporangia) in which the reproductive spores are produced.

FUNGAL SPORES: Each spore may be carried by the air to another site, where it germinates and forms another mycelium. Because spores of these fungi are common in the environment, they are often inhaled. The immune responses are usually able to prevent infection and healthy people are usually not susceptible to systemic mycoses. Elderly people and those with chronic pulmonary diseases are much more susceptible, however, and they may develop lung infections. The importance of the immune system is clearly evident if we consider people with AIDS. HIV/AIDS

Without the normal immune responses, AIDS patients are very susceptible to invasive fungal diseases, including meningitis caused by Cryptococcus. Pneumocystis jiroveci (formerly P.carinii and classified with the protozoa, its DNA sequences suggest it is closer to the fungi) is an important cause of pneumonia in people with AIDS. This species is usually not pathogenic, because the healthy immune system can easily control it. For AIDS patients, however, this form of pneumonia is often the cause of death.

RELATED;

1.  OPPORTUNISTIC MYCOSES

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