MCQs PATHOLOGY: FUNGI

8.1 Which organism is classed as eucaryotic? A. Candida albicans B. Micropolyspora faeni C. Nocardia astéroïdes D. Streptobacillus moniliformis E. Streptomyces madurae.

8.2 Which one of the following is NOT a property of Candida albicans? F. Budding yeast forms contain mitochondria G. Grows as a pseudomycelium in the tissues H. Hyphal cells may enlarge to form chlamy do spores J. Inhibited by aminoglycoside antibiotics K. Produces opportunistic infections in man.

8.3 Which is the single MOST important feature which distinguishes Candida albicans from related organisms? L. Absence of capsules M. Formation of chlamydospores N. Formation of branching mycelium O. Sensitivity to Nystatin ^ Yeast-like oval budding cells.

Answers o
8.1 A. Candida albicans is a dimorphic fungus which grows as oval budding yeast cells and elongated hyphae. It has a nuclear membrane and mitochondria typical of eucaryotic cells. The other species listed are bacteria and therefore procaryotic. Confusion over the correct taxonomic position of S. madurae has led to its inclusion in the Streptomyces, Nocardia and most recently its own specific genus Actino-madura.

8.2 J. Candida albicans is resistant to antibacterial antibiotics but is inhibited by nystatin, 5-fluorocytosine, amphotericin B and by topical gentian violet dye. Selective isolation is achieved by culture on Sabouraud's glucose agar medium, on which it grows luxuriantly, the surface growth as budding yeast forms and the submerged growth as mycelium. Distinctive chlamydospores are formed in cultures grown on corn meal agar. The organism forms part of the normal commensal flora of the upper respiratory tract, the gut, and female lower genital tract. It may become invasive in debilitated immunosuppressed individuals, or after prolonged treatment with broad spectrum antibiotics (e.g. tetracyclines). The best known clinical infection is thrush.

8.3 M. Chlamydospores are specialized thick walled spherical, 6—9 ì diameter resting phase yeast cells which differentiate at the tips of branching hyphae when the organism experiences nutritional deprivation, as when, cultured on the nutritionally poor medium "corn meal agar". Chlamydospores are a characteristic feature of Candida albicans whereas the other features listed are not distinguishing properties.

QUESTION
8.4 Which statement about dermatophytes is FALSE? Q. Dermatophytes are skin-associated parasitic bacteria R. Dermatophytoses are exemplified by athlete's foot and ringworm S. They are classified according to their characteristic morphology T. They infect only keratinized tissues U. Sabouraud's glucose agar medium is used for their isolation.

Answers
8.4 Q. Dermatophytes are not bacteria but a group of parasitic fungi which cause superficial, non-invasive infections of keratinized tissues, namely skin, hair and nails. They are classified by their colonial and cellular morphology after growth on Sabouraud's glucose agar at 20°C into three groups, trichophyton, epidermophyton and microsporum. The superficial mycoses they cause include tinea pedis (athlete's foot) — T. mentagrophytes and E. floccosum) tinea corporis (ringworm of the body — T. glabrosa) and tinea capitis (ringworm of the scalp — M. audouini and M. canis). Most epidemic ringworm infections are transmitted by infected children either directly or indirectly through combs, hair clippers and chair backs whereas sporadic infections may come from infected animals (dog, cat and horse). Athlete's foot is spread by indirect contact through contamination of the floor in communal showers and swimming pools. Griseofulvin is used successfully in both athlete's foot and ringworm. When given orally it is incorporated into newly formed keratin where it has anti-fungal activity