Question Bank 4 -YEAST



A) Candida

1. Yeasts are single-celled budding organisms, do not produce mycelia.

2. Colonies of yeast are usually visible on the plates in 24-48 hours. Their soft, moist colonies resemble bacterial cultures.

3. Candida is divided into two broad categories; albicans and non-albicans species.

4. There are several species of the genus Candida that cause diseases, infections caused by all species of Candida are called Candidiasis.

5. Candida albicans is an endogenous organism, found in 40-80% of normal human beings.

6. Candida albicans is present in the mouth, gut, and vagina ,as a commensal or a pathogenic organism.

7. The establishment of candidial infection appears to be a property of the host - not the organism, more debilitated the host, the more invasive the disease.

8. Candidial Infections usually occur when a patient has some alteration in cellular immunity, normal flora or normal physiology.

9. Prolonged antibiotic or steroid therapy destroys the balance of normal flora in the intestine allowing the endogenous Candida to overcome the host.

10. Although Candida most frequently infects the skin and mucosae and can cause pneumonia, septicemia, endocarditis, esophagitis, etc. in the compromised patient.

11. The clinical material that is sent to the laboratory for Candidiasis depends on the presentation of the disease: blood cultures, vaginal discharge, urine, feces, nail clippings or material from cutaneous or mucocutaneous lesions.

12. Candida is polymorphic yeast, i.e., yeast cells and pseudohyphae are produced.

13. [pic][pic]

14. The yeast form is 10-12 microns in diameter, gram positive, and it grows in 2 or 3 days on most bacterial and fungal media.

[pic] Candida colony

[pic] Candida albicans

15. Spores (chlamydospores) may be formed on the pseudomycelium which can be used to identify different species of Candida.

16. [pic] chlamydospores of Candida

17. Candida albicans (specifically) also produces germ tubes which serve as a key to speciation.

18. [pic]Germ tube of Candida albicans

19. The drug of choice for vaginitis and cutaneous infections is nystatin (topical) and those for systemic infections are itraconazole and fluconazole.

B. CRYPTOCOCCOSIS (Cryptococcus neoformans)

1) Cryptococcosis manifests itself most commonly as meningitis but in recent years pulmonary infections have been recognized.

2) Cryptococcosis Infections may be subacute or chronic,death usually occurs due to cerebral edema and increased intracranial pressure.

3) .Capsule of

Cryptococcus neoformans

4) C. neoformans is very distinctive yeast. The cells, which are spherical, and 5-10 microns in diameter, produce buds that characteristically are narrow-based and a polysaccharide capsule surrounds the organism.

5) Capsule of Cryptococccus neoformes [pic]

6) The polysaccharide capsule may suppress T-cell function and can be considered a virulence factor.

7) C. neoformans also produces an enzyme called phenoloxidase (melanin) which appears to be another virulence factor.

8) The ecological niche of C. neoformans is pigeon and chicken droppings.

9) Infection and disease production is probably a property of the host--not the organism.

10) The portal of entry of C. neoformans is the respiratory system,in addition to causing meningitis, C. neoformans may occasionally infect lungs and skin.

11) The disease in the lungs and skin is characterized by the formation of a granulomatous reaction with giant cells.

12) C.neoformans in lungs[pic]

13) In culture the C. neoformans grows as creamy, white, mucoid (because of the capsule) colonies.

14) [pic][pic]

15) C. neoformans growth in culture is usually visible in 24-48 hours, as the culture ages, it turns brown due to a melanin produced by the phenoloxidase.

16) C. neoformans is a round, single cell, yeast surrounded by a capsule,species identification is based on physiological reactions.

17) Pathologists use a mucicarmine stain, which tints the capsule, to identify the organism in tissue sections.

18) [pic]

19) [pic]

20) The Direct Fluorescent Antibody test identifies the organism in culture or tissue section specifically, by causing the yeast cell wall to fluoresce green.

[pic] [pic]

21) To test the patient's serum for the presence of C. neoformans there are 3 serologic tests:

• The Indirect Fluorescent Antibody test,

• The Tube Agglutination test for antibody,

• Latex Agglutination test for antigen.

22) .The drugs of choice to treat cryptococcus infection are amphotericin B plus 5-flucytosine (5-FC) or amphotericin plus fluconazole.

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Cryptococcosis ,mucramine stain

Cryptococcosis of lung in patient Methenamine silver stain.

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