Fungal CBL

Question 1

Describe the mode of action of anole drugs. What fungal infections are they used to treat?

Answer 1

Azole antifungals inhibit Cytochrome P450-dependent enzyme lanosterol 14-alpha-demethylase that catalyzes lanosterol to ergosterol. Fluconazole protects patients against YEASTS.

Question 2

Describe the mode of action of Nystatin. What infections is this used to treat?

Answer 2

This ionophore binds ergosterol and creates pores for K+ leakage and acidification of fungus. Used to treat Candida albicans.

Question 3

What is the recommended treatment for cryptococcal meningitis? What are some alternatives?

Answer 3

Flucanazole;

Flucytosine, amphotericin

Question 4

What is the principal drug of choice for pneumocystic pneumonia?

Answer 4

Pentamidine

Question 5

What fungus displays dimorphism when observed by definitive diagnosis?

Answer 5

Sporothrix schenckii;

exists as a cigar-shaped yeast inside host (35 - 37 C), but a branching hyphae in outside environments (25 C)

Question 6

What is the drug of choice to treat lymphocutaneous sporotrichosis (caused by sporothrix schenckii)

Answer 6

Itraconazole or Potassium solution (of potassium iodide)

Question 7

What is the drug of choice to treat an infection of Aspergillus Fumigatus.

Answer 7

Caspofungin

Question 8

What is the antifungal drug of choice to treat a Candida albicans infection?

Answer 8

Nyastatin - applied topically to treat mucocutaneous candidiasis

Question 9

This fungus creates white patches on the lining of the oral cavity when infecting a patient. A smear of the scraping reveals budding yeasts + pseudohyphae, BUT it forms elongating buds in plasma culture. What is this?

Answer 9

Candida albicans

Question 10

What phase structures do Candida albicans fungi form on commeal agar?

Answer 10

Hyphae or pseudohyphae, microconidia and chlamydospores

Question 11

What is the clear histological feature of a stained smear of leukocytes from the yeast infection of Histoplasma capsulatum?

Answer 11

“Buffy coat” of intracellular yeast forms in the stained blood smear of H. Capsulatum infection.

Question 12

A gardener develops a slow-growing nodule on his forearm that turns into an ulcerated lesion. Microscopy of the infection in the serum reveals elongate budding yeast that DO NOT form germ tubes. What is the fungus?

Answer 12

Sporothrix schenckii

Question 13

Where can someone contract Histoplasma capsulatum fungal infection?

Answer 13

Caves, bird/bat droppings in the Midwestern US.

Question 14

What are the 2 ways to diagnose a Histoplasma capsulatum fungus?

Answer 14

Rapid serum antigen (red) test or Urine Antigen test (yellow).

Question 15

Describe the general forms of dimorphic pathogenic fungi.

Answer 15

“Mold in the cold. Yeast in the heat.” In the environment, many fungi such as Sporothrix schenckii grow hyphae (25 C); whereas, in the body they become budding yeasts (35 C).

Question 16

What common clinical disease do immunocompromised people get when infected with pathogenic fungi?

Answer 16

Disseminated disease such as Hepatosplenomegaly (esp. in AIDS patients)

Question 17

What media can fungi grow on. Describe its contents.

Answer 17

Sabouraud media contains proteins hydrolysate and glucose plus antibiotics to prevent bacterial contamination.

Question 18

List the 3 staining techniques for fungal diseases.

Answer 18

1. KOH - kills mammalian cells, allowing one to see fungi
2. Calcofluor white staining
3. Methenamine silver/ PAS stains (not present in all labs)

Question 19

What is the drug of choice to treat an infection by Sporothrix Schenckii?

Answer 19

Itraconazole - binds P450 complex enzyme to lower the production of ergosterol. Used to treat lymphocutaneous sporotrichosis infection.

Question 20

What are the 3 clinical symptoms of Aspergillus infection?

Answer 20

1. Allergic Bronchopulmonary Asperigillosis (ABPA) = Type 1 Hypersensitivity (high IgE)
2. Aspergillomas = solid balls of fungus within the lungs
3. Angioinvasive aspergillosis @ immunocompromised patients. Disseminates throughout the body.

Question 21

What is the diagnostic morphology of Aspergillus Fumigatus on a culture? What of chest X-ray?

Answer 21

“Acute-angled branching” filamentous hyphae. CT or chest X-ray reveals “halo sign” ring-enhancing lesions in the lungs.

Question 22

What is the drug of choice for treating Aspergillus Fumigatus?

Answer 22

Itraconazole/ Voriconazole (for local infections) or Amphotericin B (if systemic).

Question 23

A women with AIDS visits her PCP complaining of discomfort and a musty smell from vaginal discharge. A KOH prep of a high vaginal swab revealed budding yeasts with pseudohyphae. What is the fungus?

Answer 23

Candida albicans treated by Fluconazole and Nystatin (preferred).

Question 24

What does Candida albicans form in the cold (20 C)? What of in warmer temps (37 C)?

Answer 24

1. Pseudohyphae in budding yeasts @ 20 C, in the environment

2. Hyphae (Germ tubes) @ 37 C, in the body

Question 25

What are common clinical symptoms from Candida albicans infection?

Answer 25

1. Thrush in immunocompromised patients 2. Vaginal Candidiasis ( < 4 pH, no change in normal pH) 3. Candida Esophagitis in AIDS patients (<100 CD4 counts)

Question 26

What fungal infection is transmitted by inhalation near pigeon droppings/ tree bark and has a heavily capsulated budding yeast form? What is the treatment?

Answer 26

Cryptococcus neoformans - treated by Amphotericin B and Fluconazole

Question 27

List 3 clinical symptoms that can result from an infection of Cryptococcus neoformans?

Answer 27

1. Cryptococcal pneumonia (cough) 2. Meningitis in immunocompromised pts. (CSF spread) 3. Fever

Question 28

What is the diagnostic morphology of Cryptococcus neoformans?

Answer 28

India ink outlines "halos" or heavily encapsulated spherical budding yeasts. "Soap bubble lesions" in imaging of the brain's grey matter.

Question 29

What fungal infection is indicated by "ground glass" of interstitial infiltrate on a CT scan and oval cysts in methanamine silver? What is the preferred treatment?

Answer 29

Pneumocystis jirovecii = common cause of pneumocystic pneumonia in AIDS patients; treated with Pentamidine (and sulfa drugs) or TMP/SMX (for prophylaxis)

Question 30

List at least 3 clinical symptoms linked to a Pneumocystis jirovecii infection.

Answer 30

1. Non-productive cough (bilateral interstitial shadowing on chest radiographs). 2. Low-grade fever 3. Dyspnea

Question 31

What diagnostic technique(s) can be used to visualize Pneumocystis jirovecii?

Answer 31

Bronchoalveolar lavage (BAL) and methanamine silver to visualize oval cysts

Question 32

What antifungal agent works by binding ergosterol to disrupt fungal membranes?

Answer 32

Amphotericin B (a polyene)

Question 33

What virulence factor is essential for Cryptococcus neoformans to spread to the CNS to causes meningitis?

Answer 33

Polysaccharide capsule ("halos" visualized on India Ink)

Question 34

A professional window-washer was cleaning some bird droppings off the side of a skyscraper when a gust of wind gave him a whiff of the feces. A few weeks later he develops pneumonia. What pathogenic fungus is the cause of this? Describe some morphological features in culture.

Answer 34

Histoplasma capsulatum - grows as hyphae and forms conidia in culture