FUNGI (moulds or mycelial fungi, and yeasts)

The chief fungal diseases of humans are infections of the skin, including 'ringworm' 'athletes foot' infections of the nails and candidiasis (thrush). Apart from these, fungi are a relatively uncommon cause of human disease. However, they are important agents of food poisoning and, on the positive side, vital in the production of most of the antibiotics used to treat a vast range of microbial infections.

Structure of a typical mould

A brief consideration only is required, using the terms mycelium and hypha. The structure of the hyphae, including the wall, membrane, cytoplasm and nuclei (cf bacteria, which lack a nucleus), is required.

Students should be aware of the ability of moulds to form large numbers spores, for rapid reproduction and dispersal, rather than surviving adverse conditions.
Students will only be expected to recognise spore production when shown in diagrams.

Structure of yeast

This is included on account of the fact that non-pathogenic yeasts, which are readily observable using the high power of the microscope, can serve as safe models for investigating certain principles, such as population growth, of pathogenic bacteria.

Background

Ringworm infections are caused by a number of moulds having a mycelium of narrow, septate hyphae which appear in the epidermis of the skin. The parasitic fungi causing athlete's foot are species of Trichophyton. The yeast Candida albicans is normally a harmless inhabitant of the skin and sometimes, the fungus can attack the skin, or the lining of the mouth or vagina. This occurs when a person's resistance to infection is low, as may happen during illnesses such as diabetes, or when the natural protective microbial inhabitants of body surfaces are disturbed by medical treatment (e.g. with antibiotics. or steroids) for some medical condition. The fungus can exist in two forms, according to conditions. In one form, the fungus consists of yeast-like cells: the other form consists of short, narrow, septate branched hyphae which can form a loose and ill defined mycelium.

Both Trichophyton and Candida produce spores.