Fungal CBL Flashcards
Describe the mode of action of anole drugs. What fungal infections are they used to treat?
Azole antifungals inhibit Cytochrome P450-dependent enzyme lanosterol 14-alpha-demethylase that catalyzes lanosterol to ergosterol. Fluconazole protects patients against YEASTS.
Describe the mode of action of Nystatin. What infections is this used to treat?
This ionophore binds ergosterol and creates pores for K+ leakage and acidification of fungus. Used to treat Candida albicans.
What is the recommended treatment for cryptococcal meningitis? What are some alternatives?
Flucanazole;
Flucytosine, amphotericin
What is the principal drug of choice for pneumocystic pneumonia?
Pentamidine
What fungus displays dimorphism when observed by definitive diagnosis?
Sporothrix schenckii;
exists as a cigar-shaped yeast inside host (35 - 37 C), but a branching hyphae in outside environments (25 C)
What is the drug of choice to treat lymphocutaneous sporotrichosis (caused by sporothrix schenckii)
Itraconazole or Potassium solution (of potassium iodide)
What is the drug of choice to treat an infection of Aspergillus Fumigatus.
Caspofungin
What is the antifungal drug of choice to treat a Candida albicans infection?
Nyastatin - applied topically to treat mucocutaneous candidiasis
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?
Candida albicans
What phase structures do Candida albicans fungi form on commeal agar?
Hyphae or pseudohyphae, microconidia and chlamydospores
What is the clear histological feature of a stained smear of leukocytes from the yeast infection of Histoplasma capsulatum?
“Buffy coat” of intracellular yeast forms in the stained blood smear of H. Capsulatum infection.
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?
Sporothrix schenckii
Where can someone contract Histoplasma capsulatum fungal infection?
Caves, bird/bat droppings in the Midwestern US.
What are the 2 ways to diagnose a Histoplasma capsulatum fungus?
Rapid serum antigen (red) test or Urine Antigen test (yellow).
Describe the general forms of dimorphic pathogenic fungi.
“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).
What common clinical disease do immunocompromised people get when infected with pathogenic fungi?
Disseminated disease such as Hepatosplenomegaly (esp. in AIDS patients)
What media can fungi grow on. Describe its contents.
Sabouraud media contains proteins hydrolysate and glucose plus antibiotics to prevent bacterial contamination.
List the 3 staining techniques for fungal diseases.
- KOH - kills mammalian cells, allowing one to see fungi
- Calcofluor white staining
- Methenamine silver/ PAS stains (not present in all labs)
What is the drug of choice to treat an infection by Sporothrix Schenckii?
Itraconazole - binds P450 complex enzyme to lower the production of ergosterol. Used to treat lymphocutaneous sporotrichosis infection.
What are the 3 clinical symptoms of Aspergillus infection?
- Allergic Bronchopulmonary Asperigillosis (ABPA) = Type 1 Hypersensitivity (high IgE)
- Aspergillomas = solid balls of fungus within the lungs
- Angioinvasive aspergillosis @ immunocompromised patients. Disseminates throughout the body.
What is the diagnostic morphology of Aspergillus Fumigatus on a culture? What of chest X-ray?
“Acute-angled branching” filamentous hyphae. CT or chest X-ray reveals “halo sign” ring-enhancing lesions in the lungs.
What is the drug of choice for treating Aspergillus Fumigatus?
Itraconazole/ Voriconazole (for local infections) or Amphotericin B (if systemic).
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?
Candida albicans treated by Fluconazole and Nystatin (preferred).
What does Candida albicans form in the cold (20 C)? What of in warmer temps (37 C)?
- Pseudohyphae in budding yeasts @ 20 C, in the environment
2. Hyphae (Germ tubes) @ 37 C, in the body
What are common clinical symptoms from Candida albicans infection?
- Thrush in immunocompromised patients
- Vaginal Candidiasis ( < 4 pH, no change in normal pH)
- Candida Esophagitis in AIDS patients (<100 CD4 counts)
What fungal infection is transmitted by inhalation near pigeon droppings/ tree bark and has a heavily capsulated budding yeast form? What is the treatment?
Cryptococcus neoformans - treated by Amphotericin B and Fluconazole
List 3 clinical symptoms that can result from an infection of Cryptococcus neoformans?
- Cryptococcal pneumonia (cough)
- Meningitis in immunocompromised pts. (CSF spread)
- Fever
What is the diagnostic morphology of Cryptococcus neoformans?
India ink outlines “halos” or heavily encapsulated spherical budding yeasts. “Soap bubble lesions” in imaging of the brain’s grey matter.
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?
Pneumocystis jirovecii = common cause of pneumocystic pneumonia in AIDS patients; treated with Pentamidine (and sulfa drugs) or TMP/SMX (for prophylaxis)
List at least 3 clinical symptoms linked to a Pneumocystis jirovecii infection.
- Non-productive cough (bilateral interstitial shadowing on chest radiographs).
- Low-grade fever
- Dyspnea
What diagnostic technique(s) can be used to visualize Pneumocystis jirovecii?
Bronchoalveolar lavage (BAL) and methanamine silver to visualize oval cysts
What antifungal agent works by binding ergosterol to disrupt fungal membranes?
Amphotericin B (a polyene)
What virulence factor is essential for Cryptococcus neoformans to spread to the CNS to causes meningitis?
Polysaccharide capsule (“halos” visualized on India Ink)
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.
Histoplasma capsulatum - grows as hyphae and forms conidia in culture
