MCQs on Fungi culture and identification methods: Medical microbiology

                         MCQs on Fungi culture and identification

1. A 43-year-old woman, presents to her dermatologist with complaints of persistent, itchy skin lesions on her arms and legs. She describes the lesions as red, scaly patches that have been gradually spreading over the past few weeks. The patient has a history of diabetes, and her blood glucose levels have been fluctuating recently.

Upon examination, the dermatologist observes erythematous, annular lesions with a raised border on the patient's arms and legs. Some lesions have a central clearing, typical of a fungal infection. Considering her medical history, the dermatologist suspects a dermatophyte infection, possibly tinea corporis.

The dermatologist collects skin scrapings from the edge of one of the lesions using a scalpel blade. The collected specimen is placed in a sterile container. The skin scrapings are sent to the microbiology laboratory for fungal culture. Mycosel agar, a specialized medium for dermatophytes, is used. The culture media containing cycloheximide and chloramphenicol is used.

The cultures are incubated at 30°C, after incubation, the fungal cultures are examined microscopically. The presence of hyphae and conidia is observed, suggesting a dermatophyte infection. The colonies on the agar plates are examined macroscopically.

To confirm the identification and determine the specific species, a subculture is performed.

Why are both cycloheximide and chloramphenicol included in the culture media?

a) To enhance fungal growth

b) To inhibit bacterial overgrowth    

c) To promote sporulation in fungi

d) To increase agar hydration

2. What is the recommended incubation period for cultures to be reported as negative for dermatophytes?

a. 7 days at 37°C

b. 14 days at 25°C

c. 21 days at 30°C

d. 30 days at 35°C

3. A 58-year-old man, is admitted to the hospital for chemotherapy treatment following a diagnosis of lymphoma. His immune system is compromised due to the immunosuppressive effects of chemotherapy. During the course of chemotherapy, the patient develops persistent fever, cough, and shortness of breath. Physical examination reveals oral thrush and skin lesions. A chest X-ray shows diffuse infiltrates in the lungs.

A blood culture is performed to identify any systemic fungal infection. The blood sample is inoculated into fungal culture media and incubated at an appropriate temperature.

Given the respiratory symptoms and infiltrates on the chest X-ray, a bronchoscopy with BAL is conducted. The collected fluid is sent for fungal culture and microscopic examination. A biopsy of one of the skin lesions is taken to determine the cause of the cutaneous manifestations. The tissue sample is processed for histopathological examination and fungal culture.

Candida albicans is isolated from the blood culture, indicating disseminated candidiasis. Histopathological examination of the skin biopsy demonstrates the presence of yeast cells with a thick capsule consistent with Cryptococcus neoformans.

The BAL culture reveals the presence of blue-green colonies with surface consisting of a dense felt of conidiophores on culture media within a week after the incubation.Which of the following fungus is the possible fungus isolated from the lung infection?

a) Aspergillus fumigatus

b) Cryptococcus neoformans

c) Histoplasma capsulatum

d) Trichophyton tonsurans 

4. Which automated blood culture system is mentioned as adequate for the recovery of yeasts, excluding Malassezia spp.?
a. BACTEC
b. BacT/ALERT
c. VersaTREK
d. All of the above      

5. For cerebrospinal fluid (CSF) collected for fungal culture, what is the purpose of filtering it through a 0.45-mm membrane filter?
a)  To enhance yeast growth
b) To concentrate the sediment
c) To prevent bacterial overgrowth    

d) To remove fungal contaminants

6. What is the recommended temperature for storing cerebrospinal fluid specimens if prompt processing is not possible?
a. 4°C
b. 25°C (Room temperature)    
c. 30°C
d. -20°C

7. What alternative systems or media are encouraged for laboratories frequently recovering dimorphic fungi from blood?
a. Antibiotic-containing media

b. Cold enrichment medium
c. Lysis-centrifugation system (Isolator)     
d. Routine blood agar plates

8. What is the optimal temperature for fungal blood cultures, and how long is the suggested incubation time?
a. 25°C, 21 days     

b. 30°C, 14 days
c. 35°C, 10 days
d. 37°C, 7 days

9. For eye specimens such as corneal scrapings, what is the recommended pattern for inoculation onto noninhibitory media?
a. Random distribution
b. Random distributionx

c. Straight line    

d. X-shaped pattern 

10. How should vitreous humor aspiration be processed for fungal culture?
a. Concentrate by centrifugation, using the sediment for smears and culture      

b. Discard the specimen
c. Dilute with saline before culture
d. Direct inoculation onto media

11. What is the recommended storage condition for urine samples if processing is delayed?

a. Room temperature

b. 4°C

c. -20°C

d. 30°C

12. For tissue, bone marrow, and sterile body fluids, what is critical during processing to enhance fungal recovery?

a. Drying

b. Freezing

c. Grinding

d. Mincing    

13. Which agar is often used for the cultivation of Cryptococcus spp. from cerebrospinal fluid (CSF), pleural fluid, bone marrow, tissue, and lower respiratory specimens?

a. Birdseed agar    

b. Blood agar

c. Mycosel agar

d. Sabouraud dextrose agar

14. What is the primary purpose of Brain-heart infusion agar in fungal culture?

a. Detection of ascospores in ascosporogenous yeasts

b. Isolation of yeasts

c. Primary recovery of pathogenic fungi

d. Recovery of dermatophytes

15. Which agar is used for the presumptive identification of yeast and filamentous fungi based on characteristic color changes?

a. Chromogenic agar

b. Inhibitory mold agar

c. Mycosel agar

d. Sabouraud Dextrose with Brain Heart Infusion (SABHI) agar

16. Dermatophyte test medium changes color from red to yellow due to:

a. Alkaline metabolites produced by dermatophytes

b. Acidic metabolites produced by dermatophytes

c. Enzymatic reactions with chromogens

d. Presence of urease-producing fungi

17. Which media enhances the recovery of Blastomyces and Histoplasma capsulatum from contaminated specimens?

a. Mycosel agar

b. Potato flake agar

c. Sabouraud Dextrose with Brain Heart Infusion (SABHI) agar

d. Yeast-extract phosphate agar

18. Christensen’s urea agar is used for the identification of:

a. Ascosporogenous yeasts

b. Cryptococcus, Trichosporon, and Rhodotorula spp.

c. Candida albicans by chlamydospore production

d. Yeasts with urease-producing capabilities

19. What is the purpose of adding Tween 80 and trypan blue to Cornmeal agar?

a. Enhance sporulation of yeasts

b. Inhibit bacterial growth

c. Provide a contrasting background for observing morphologic features

d. Stimulate chlamydospore production

20. Which of the following culture medium is used for the confirmation of Cryptococcus spp.?

a) Cottonseed conversion agar

b) Nitrate reduction medium

c) Rice medium

d) Yeast fermentation broth

Yeast fermentation broth is used for the identification of yeasts by determining fermentation. What is the specific carbohydrate utilized in this medium?

a) Dextrose

b) Maltose

c) Raffinose

d) Sucrose

22. Which of the following describes the typical colony appearance of yeasts in the clinical laboratory?

a. Cottony

b. Fluffy

c. Moist, creamy, opaque

d. Woolly

23. How are filamentous fungi or molds characterized in terms of colony appearance?

a. Cottony, woolly, powdery

b. Fluffy, pasty

c. Moist, creamy, opaque

d. Smooth, shiny

24. 

Answers:

1. b) To inhibit bacterial overgrowth    

2. c) 21 days at 30°C

3. a) Aspergillus fumigatus

4. d. All of the above 

5. c) To prevent bacterial overgrowth   

6. b) 25°C (Room temperature) 

7. c) Lysis-centrifugation system (Isolator)    

8. a) 25°C, 21 days

9. d) X-shaped pattern 

10. a) Concentrate by centrifugation, using the sediment for smears and culture         

11. b) 4°C

12. d) Mincing 

13. a) Birdseed agar

14. c) Primary recovery of pathogenic fungi
15. a) Chromogenic agar

16. b) Acidic metabolites produced by dermatophytes

17. c) Sabouraud Dextrose with Brain Heart Infusion (SABHI) agar

18. b) Cryptococcus, Trichosporon, and Rhodotorula spp.

19. a) Enhance sporulation of yeasts

20. b) Nitrate reduction medium

21. a) Dextrose

22. c) Moist, creamy, opaque

23. a) Cottony, woolly, powdery