(by Mintcho Petkov)
Fungi are a kingdom of organisms which resemble plants in that, with few exceptions, they have definite cell walls and are usually non motile (although they might have motile reproductive cells).
Fungi differ from plants in that they do not contain clorophyll and therefore they are not autotrophs. Fungi can be either saprobic (feeding on dead organic matter) or parasitic (feeding on living organic matter).
Almost all fungi which are parasites on humans are species of the class Deuteromycetes or more commonly known as `imperfect fungi',called that way because they lack the sexual stage in their development. The conidial stages of many of these fungi resemble the conidial stages of some well known Ascomycetes and the presumption of the scientists today is that most of the Fungi Imperfecti actually represent Ascomycetes , whose ascigerous stage is either rarely produced in nature or was eliminated through the evolutionary process. A strong evidence for this conclusion is that in some cases the missing ascigerous stages have been discovered in nature later or have been produced in laboratory conditions.
Species of Candida are normal inhaitants of the mouth, throat, digestive tract and vagina of the human body; they are described as dimporphic, because they produce yeastlike cells under certain conditions and branching filaments with a mycelial habit of growth under other conditions.
They can produce diseases of any of the areas of the human body in which they are found and can also cause systematic infection with brain, meningal or heart involvement.
Fungi of this family cause infections on the skin, nails and scalp and they constitute around 30 out of about 55 species of fungus considered to be pathogenic for man. Leisions caused by dermatophytes are usually circular and tend to enlarge equally in all directions. These fungi usually affect the superficial keratin-rich layer of the affected areas. They hydrolyze the keratin but only very slowly and can survive eveni in its absence.
In the past it was thought that these infections were caused by worms or lice and therefore the names of the diseases: ringworm or tinea, further qualified by the name of the body area affected( tinea capitis - ringworm of the scalp, tinea pedis - athlete's foot etc. ). There are three pathogenic genera of Dermatophytes - Microsporum, Trichophyton and Epidermophyton.
Following is a list of the most common dermatophytic infections:
It is caused by species of Microsporum and Trichophyton. The disease varies from small itching on the scalp to severe cases which can cause permanent baldness. Some of the infections can result in painful inflammations and pustular abcesses around the hair follicles.The disease is sometimes highly contagious transmitted either directly or via hair clippers and other fomites. Tinea capitis is seen in two forms: endothrix infections, with the hyphae growqing only within the hair and ectothrix infections, with growth within and on the surface of the haird shaft.
This is the disease more commonly known as ringworm of the smooth skin. The leisions are usually circular with a scaly center, surrounded by an advancing circle of vesicles and papules.The leisions may itch, particularly in warm weather. Tinea corporis is caused by species of Microsporum and Trichophyton.
or more commonly known as `barber's itch' affects the bearded area of the face and neck, forming dark red abcessess. The hairs in the affected areas become brittle and lack luster. It is caused by members of Trichophyton and more rarely Microsporum.
or `athlete`s foot` is the most common fungus infection , most of the cases being caused by T. mentagrophytes. It results in an inflammatory infection with vesicles between the toes and on the soles; the skin peels and fissures form in the affected areas. The infection can sometimes spread to hands,thighs and other areas.
is sometimes called onychomycosis, or ringworm of the nails. The nails become opaque and brittle, lose luster and are easily separated from the nail bed. The infection is caused by E. floccosum or various species of Trichophyton.
The fungi that cause deep-seated mycoses are soil saprophytes, which when inhaled produce chronic infections that progress slowly at first but accelerate and finally lead to death.
B. dermatitidis is dimorphic, with mycelial growth in laboratory conditions at room temperature, but yeast-like in infected tissues at body temperature. It is found in soil, but less commonly than other pathogenic fungi. B. dermatitidis causes North American blastomycosis.
This fungus is dimorphic, too. It forms yeastlike cells in the mononuclear cells of the peripheral blood and macrophages in bone marrow and spleen, but grows in a mycellial form in a laboratory media at room temperature. This fungus causes Histoplasmosis - a very common and serious disease.
This fungus is monomorphic yeastlike fungus ( it does not produce mycellial growth under any conditions). It causes a form of meningitis.
P. ovale does not cause any disease, but because of its close association with dandruff ( it is most commonly cultivated from it in laboratory conditions) it was reported to be the cause of dandruff, but claims have nowadays been disproven. P. ovale is in fact a yeast from the family cryptococcaceae present on the skin as a part of the normal body flora. An evidence for its being indigenous to the human body is the abundance of the substances it needs for its growth in the skin - fat, fatty acids and glycerol.
The diagnosing of fungus infections can be done through microscopic examination of a tissue sample after it is made transparent through warming it up with 10 per cent solution of NaOH or KOH, or by examination of the affected areas with ultraviolet light, which produces fluorescence with some fungi.
The treatment of fungus infections is a slow process, which may include external treatment with undecylenic acid or other fatty acids, thymol, salycilic acid, iodine, various ointments or antifungal agents and sometimes internal application of big doses of the antibiotic griseofulvin.
1) MICROBIOLOGY, fourth edition, by Philip L. Carpenter
2) INTRODUCTORY MYCOLOGY, second edition, published by JOHN WILEY & SONS, INC.
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