Short Notes on Imperfect Fungi

The below mentioned article provides a short note on Imperfect Fungi:- 1. Introduction to Imperfect Fungi 2. Candida 3. Blastomyces Dermatitidis and Cryptococcus Neoformans Cause Blastomycosis.

Introduction to Imperfect Fungi:

Many imperfect fungi have septate hyphae and asexual conidia resembling those of Ascomycetes, but sexual or “perfect” state has not yet been described for these fungi—hence they are called as Fungi imperfecti. A majority of the pathogenic moulds, yeasts, yeast-like fungi (candida) and dimorphic fungi (Histoplasma, Paracoccidioides) belong to this group—Fungi imperfecti.

Sporotrichum has a septate mycelium. Lateral branches extend from the hyphae bearing single conidia or clusters of conidia at their sides or ends. The Sporotrichum grows on common nutrient media (pH 6.5) producing the best growth on Sabouraud’s medium at 25 to 28°C. Growth is slow. The colonies are leathery, fluffy, smooth or folded and quite frequently pigmented.

This causative agent enters the subcutaneous tissue and the lymph nodes through abrasions of the skin; as a result gumma similar to that in syphilis and tuberculosis are produced in the pharynx, larynx, muscles and synovial membrane. It may also cause abscess of the bones, joints and internal organs. Antibiotics and sulphonamides have no effect.

Candida:

They are unicellular organisms which reproduce by budding. Neither conidia nor ascospores are produced. They possess no true mycelium; the pseudo-mycelium is devoid of a membrane and septa and develops by successive or terminal budding .

Candida albicans and C. tropicalis are most important in human pathology. About 20 species of the genus Candida are human pathogens and are present on the skin and mucous membrane of the mouth, gastrointestinal tract and urinogenital organs of man. They occur on fruit, vegetables and other foodstuffs, in bath sewage, washing from catering establishments, and on dishes.

The infection is acquired when body is weakened and in the presence of unfavorable conditions (increased moisture, skin maceration, long term occupational contact with sugar containing fruit and vegetables, inadequately disinfected baths). Debilitated children, bath­house attendants, confectioners are susceptible to candidiasis.

Candidiasis associated with the long term use of antibiotics (penicillin, chlortetracycline etc.) have become of great importance.

They cause profound disturbances of symbiotic relationship among normal micro-flora resulting into a condition of dysbacteriosis which enhances intensive multiplication, spread into the buccal, intestinal and vaginal mucosa and their transformation from the saprophyte state into conditionally pathogenic and pathogenic forms. As a result, local and general lesions develop.

The yeast like fungi affect the skin between the fingers and toes in the inguinal and axillary folds, the nails and nail folds, the mucous membrane of the lips and mouth corners, the tongue, fauces, oesophagus, and sometimes the vagina with the development of white films. Infection of the mucosa is known as “Thrush“.

The gastrointestinal, respiratory, urogenital and nervous system, liver, biliary tract, pancreas, bones, kidney are also involved in candidiasis. The most common Candida infection is vaginitis or vaginal thrush which is characterised, in pregnant women, by a whitish discharge with a pH below 5.2, and, microscopically, some pus cells and many yeasts, including pseudo mycelium, can be seen.

In infection due to trichomonas and bacteria, the discharge is more purulent and less acid.

Oral thrush occurs in debilitated or bottle fed infants. Creamy white patches are found covering red, raw areas of mucous membrane and tongue. It also occurs in adults in angular cheilitis, in sore mouth caused by ill-fitting dentures and all too frequently, after prolonged courses of oral antibacterial therapy.

Infections of the skin are common in diabetes and skin lesions are characterised by erythema, exudation and desquamation and occur most commonly in the axilla and groin, on the vulva and glans penis. It also affects the inter-digital clefts, the skin folds round the nails and sometimes nail itself.

Infections of the intestine occur in infants, the aged, and those on long courses of oral antibiotics. Symptoms are pruritus ani or diarrhoea. The organism survives well in exudate collected on swabs and may even multiply if there is delay in transmission to the laboratory.

It may be demonstrated microscopically in wet preparation or Gram-stained smears and grows readily at 25 to 28°C (room temperature). The incorporation of antibiotics in medium may inhibit the growth of other bacteria.

Characteristic of C. albicans is the production of curved, elongated germ tubes within three hours when it is transferred from peptone water to mammalian serum at 37°C. Chlamydospores of C. albicans grown on corn meal agar (Gram-stain).

On Sabouraud’s medium, after two days, C. albicans produces high convex, off-white colonies 1.5 mm in diameter. It ferments carbohydrates; but it fails to split urea; which is used in differentiating it from other yeasts, PCR is rapid and sensitive method to detect C. albicans and other yeasts in blood.

Before undertaking the treatment, it is always advisable to correct the underlying disturbances (diabetes or poor hygiene). The usual treatment is to give the polyene nystatin locally. Nystatin is very poorly absorbed from the gut so that the systemic infection must be treated with amphotericin B. Another polyene, trichomycin, is often used in vaginitis as it effective against trichomonas and Candida.

Blastomyces Dermatitidis and Cryptococcus Neoformans Cause Blastomycosis:

Blastomyces dermatitidis is a large budding cell which is microscopic, its mycelium is segmented, branching and with conidia protruding laterally. On blood agar at 37°C, the fungus produces white, moist, waxy, soft, wrinkled colonies of the yeast only. Oil Sabouraud’s medium at 25°C it produces fluffy white colonies which turn brown.

The disease becomes chronic with skin lesions on the face, hands and buttocks. Internal organs are rarely affected.

Cryptococcus neoformans is round and oval yeast like cell, with one or two buds, which is frequently surrounded by a capsule. On Sabouraud’s medium, it forms mucoid, white colonies which later become brown and creamy in colour.

This fungus causes in man a deep- seated, systemic chronic blastomycosis—commonly in agricultural workers and animal breeders. The lungs, intestine, skin, subcutaneous tissue, lymph nodes, brain, meninges and bones are involved, and the mortality is very high. Laboratory diagnosis is by microscopic examination.

The use of ineffective broad spectrum antibiotics is banned. The physical condition of the body should be strengthened. Special antibiotics (nystatin, neomycin, candicidin) are prescribed for blastomycosis and candidiasis.