Fungi Flashcards
What type of organisms are fungi compared to bacteria?
Fungi are eukaryotic, whereas bacteria are prokaryotic.
How do fungi absorb nutrients?
Fungi absorb nutrients from the environment.
What are the main components of fungal cell walls?
Fungal cell walls are made of chitin.
What conditions do most fungi prefer for growth?
Most fungi grow in aerobic conditions and prefer neutral or acidic pH.
What are the two main types of fungi?
Yeasts and molds.
What are yeasts?
Yeasts are single-celled organisms that form creamy bacterial-like colonies without aerial hyphae.
What is the typical shape of yeasts when viewed microscopically?
Yeasts are round or oval but can appear elongated, elliptical, or irregular.
How do yeasts reproduce?
Yeasts reproduce by budding, forming blastoconidia.
What structure is formed when blastoconidia do not separate?
A pseudohyphae is formed.
Under what conditions do yeasts produce true septate hyphae?
True septate hyphae are produced usually under reduced oxygen conditions.
What role do yeasts have in human flora?
Yeasts are part of the normal flora of the mouth, throat, skin, large intestine, and vagina.
Are yeasts opportunistic pathogens?
Yes, yeasts are usually considered opportunistic pathogens.
What are the most commonly encountered yeast species?
- Candida albicans
- C. tropicalis
- C. glabrata
- Cryptococcus neoformans
- Aspergillus species
- Rhodotorula rubra.
What is the appearance of most molds?
Most molds have a wooly appearance due to aerial mycelium.
What specimens are commonly selected for culture of fungi?
Respiratory secretions, including sputum, bronchial washings, and tracheal aspirations.
What should primary media for fungal culture include?
Antibacterial agents and at least one medium should contain cycloheximide.
How should CSF be processed for fungal culture?
CSF should be filtered with a 0.45um filter and inoculated onto primary media.
What is the recommended incubation temperature for blood cultures to recover fungi?
30°C for 21 days.
What agar is recommended for the recovery of dermatophytes?
Mycosel agar.
What should be done with urine before culture?
Urine should be centrifuged, and the sediment used for culture on primary media.
Which dye is considered superior for fungal microscopic examination?
Calcofluor White.
What is the most common cause of yeast infection worldwide?
Candida albicans.
What symptom does Candida enteritis produce?
Watery diarrhea not accompanied by blood, pus, or mucus.
What is the second most virulent species of Candida?
C. tropicalis is the second most virulent species of Candida
What infections is C. glabrata associated with?
- Urinary tract infections
- Vaginal candidiasis
Who commonly gets infections from C. glabrata?
Infections are commonly seen in elderly patients in hospitals that have been catheterized and given antibiotics
What does the microscopic morphology of Candida species show?
Candida species appear as large Gram-positive yeast cells that are coccoid or oval
How do Candida spp. colonies appear on blood agar?
Colonies appear as white to cream to tan color
What are germ tubes?
A germ tube is a filamentous extension of the yeast cell that is approximately 3-4X as long and half the width of the yeast cell
Which species is identified by the production of true germ tubes?
C. albicans is identified by the production of true germ tubes
What are the four different types of morphologies on cornmeal agar?
- Blastoconidia
- Pseudohyphae
- True Hyphae
- Arthroconidia
What does carbohydrate assimilation testing identify?
Carbohydrate assimilation tests are used to identify which sugars yeasts can use as a sole source of carbon
What is the gold standard for carbohydrate assimilation testing?
The API20C AUX yeast identification system is the gold standard for assimilation testing
Where is Cryptococcus neoformans commonly found?
Pigeon and other bird droppings, and in soil contaminated with pigeon droppings.
What type of pathogen is Cryptococcus neoformans?
Opportunistic pathogen.
What diseases are caused by Cryptococcus neoformans?
- Meningitis
- Pneumonia
- Bacteremia.
What is the most commonly submitted specimen for diagnosing cryptococcosis?
CSF.
What is the microscopic morphology of Cryptococcus spp.?
Round or slightly oval budding yeast cells and absence of pseudohyphae.
What does a positive India ink test indicate?
Capsule presence of Cryptococcus species.
What is the germ tube test result for C. neoformans?
Negative.
What is the Cryptococcal Latex Antigen Test used for?
Identify specific cryptococcus capsular polysaccharide antigens in body fluids.
You suspect yeast based on the gram. What does a positive urease test indicate?
Typical of cryptococcus species.
What is the phenol oxidase test result for C. neoformans?
Produces dark brown colonies on niger seed agar within 2-5 days.
What characteristic do species within the dermatophyte genera share?
Kertinophilic.
How are clinical infections of dermatophytoses typically named?
Using ‘tinea’ followed by a Latin term for the body region.
What are the two colony morphologies of Trichophyton mentagrophytes?
- Granular form
- Downy form.
What type of infections does Trichophyton tonsurans cause?
Infects skin, hair, and nails.
It is often associated with tinea capitis (scalp ringworm) in humans.
What unique characteristic do colonies of T. tonsurans develop on Sabouraud dextrose agar?
They develop a rust-colored pigment on the reverse side.
This pigment is a key identification feature for this dermatophyte.
What shape are the macroconidia of Microsporum canis?
Spindle-shaped with echinulate and thick walls.
The structure of the macroconidia is crucial for identification.
