fungus
Meaning of fungus: Closer relatives of animals than of plants, and wrapped in a cell wall humans have no equivalent of, which is what antifungal drugs exploit.
Definition of fungus
A fungus is an organism belonging to its own biological kingdom, separate from plants and animals and in fact more closely related to animals. Fungi have no chlorophyll and cannot photosynthesize, so they feed by releasing enzymes into their surroundings and absorbing what those enzymes break down. The group takes in yeasts, molds and mushrooms. The plural is fungi.
What forms do fungi take?
| Form | How it grows |
|---|---|
| Yeast | A single cell, multiplying mostly by budding a daughter cell off the side |
| Mold | Branching threads called hyphae, matting together into a network |
| Mushroom | The visible fruiting body of a larger fungus, produced only to release spores |
| Dimorphic | Switches between yeast and mold form, usually according to temperature |
Most of the fungi in soil, air and food never trouble a person. A small number cause disease, and they do it in three separate ways: by growing in or on tissue, by provoking allergy when spores are inhaled, and by producing toxins that act at a distance in contaminated food. Only the first is an infection in the strict sense.
Why are fungal infections harder to treat than bacterial ones?
Because fungal cells are built much like human cells. Both keep their genes in a nucleus and use the same kind of internal machinery, so a drug that poisons a fungal process is very likely to poison the equivalent human one. Bacteria differ from human cells in far more ways, which is what gave antibiotics so many targets to choose from. Antifungal drugs are left with a short list of genuine differences: the fungal cell wall, built from chitin and glucans that human cells never make, and ergosterol, the sterol stiffening the fungal membrane where a human cell uses cholesterol. That narrow foothold explains why there are so few classes of antifungal drug, why side effects are more of a problem, and why resistance is a growing concern.
Who develops a serious fungal infection?
Superficial infection of skin, nails, hair and the mucous membrane lining the mouth or genital tract is common in otherwise healthy people, and includes athlete's foot, ringworm and thrush. Infection that reaches the lungs, the bloodstream or deeper organs is a different matter and usually follows a weakened immune system. The recognized settings include chemotherapy, medicines taken after an organ transplant, advanced HIV infection, long courses of steroids, poorly controlled diabetes, and prolonged antibiotic treatment that clears away competing bacteria. Broken skin, burns and long standing plastic lines into a vein give fungi another route inward.
Used in a sentence
Culture of the skin scraping identified a fungus consistent with a superficial fungal infection.
Good to know
Fungi are classified in their own kingdom rather than as plants, a scientific distinction from older classification schemes that still surfaces in casual descriptions of fungi as plantlike organisms.
Word origin
Where “fungus” comes from
From Latin fungus, meaning mushroom, a name that in classical usage extended broadly to various growths of this kind.