Mycology Exam 3 (Yeast + Opportunistic) Flashcards
Describe yeasts
Eukaryotic, unicellular organisms
What morphological features are helpful in differentiating yeasts?
- Size of the cells
- Presence or absence of capsule
- Production of chlamydospores
- Broad-based or narrow-necked budding
Reproduction of yeast
Asexually by blastoconidia (budding)
Sexually by ascospores or basidiospores
Describe the budding process of yeast
Outpouching of yeast cell wall forms bud/daughter cell, cell wall septum created, daughter cell detaches from mother cell and a bud scar is left
Germ tube
Tubular outpouching of cell wall - Does NOT have a constriction at its base, initial stage of true hyphae formation
Pseudohyphae
Cell wall constrictions but no true intracellular septation
Most yeast infections caused by ______ species (also the most commonly IDed in the lab)
Candida
C. albicans complex includes:
C. candida
C. dubliniensis
C. africana
Thrush
Infection of the mucous membranes in the mouth
Toxin production of Candida sp
Candidalysin –> initiates epithelial invasion
Name standout feature noted about C. auris
Resistant to MANY antifungals, including fluconazole
Name standout feature noted about C. glabrata
Can cause endocarditis, meningitis, and disseminated disease
Trehalose positive
Name standout feature noted about C. tropicalis
Prevalent in patients with hematologic malignancies
Name standout feature noted about C. krusei
Intrinsically resistant to azoles
Name standout feature noted about C. parapsilosis complex
Primary cause of fungemia in the NICU, second most commonly isolated Candida spp. in blood cultures
True septate hyphae may be produced by Candida _______
albicans complex
Yeast cells are gram ____
positive
How do you ID C. albicans?
Colonies possess feet on agar, starlike
Production of germ tubes or chlamydoconidia
How to ID C. glabrata?
Ferments glucose and trehalose
How to ID C. tropicalis?
Ferments Sucrose and maltose
Germ Tube Test (purpose, testing time)
ID of C. albicans
Results available within 3 hours
Rapid Trehalose Test (purpose, positive color and negative color)
presumptive ID of C. glabrata
Positive color = yellow
Negative = blue/green
What is the major Cryptococcus sp and what is it associated with in nature?
C. neoformans
Associated with pigeon or other bird excreta
What is one of the most commonly isolated species in immunocompromised hosts worldwide?
C. neoformans
Pathogensis and Disease of Cryptococcus (population)
Found in immunocompromised patients, ESPECIALLY those with decreased CD4 T-cells, organism can travel to CNS and cause meningitis
What is a standout feature of Cryptococcus, microscopically?
Polysaccharide capsule that protects the yeast from dessication
Lab ID of Cryptococcus
Polysaccharide capsule that is highly refractile (can be observed with India Ink) and extreme variation in the size of the yeast cells
India Ink Stain (purpose, specimens used)
Rapid assessment tool for the ID of Cryptococcus sp.
Specimens = CSF, urine, and other body fluids
Final ID of Cryptococcus (based on culture/growth)
Brown to black color on niger seed/birdseed agar due to Phenoloxidase oxidizing to melanin (ONLY produced by C. neoformans)
Standout Info : Geotrichum spp.
Major organism = G. candidum
Normal human microbiota
Rectangular arthroconidia on cornmeal agar
How is Geotrichum differentiated from Trichosporon spp?
Urease testing
Trichosporon = positive urease
Geotrichum = negative urease
Standout features of Rhodotorula spp.
- Found in fruit juice, milk, or salt and freshwater
- Normal skin flora
- R. mucilaginosa is relevant species
- Coral pink to salmon-colored colonies
- Associated with fungal peritonitis in patients on CAPD
- Urease positive
- Produce capsules
Standout features of Saccharomyces spp.
S. cerevisiae = major organism
AKA baker’s yeast
Common yeast found in baking and probiotics
Rarely associated with disease
Why is there an increased incidence of Saccharomyces cerevisiae infections?
Use of probiotics for treatment of antibiotic-associated diarrhea
Contact with health foods containing the organism
Most opportunistic fungal pathogens that are encountered in the lab are considered what term? Should they be considered/reported?
Saprobes - saprophytic/environmental organisms
YES - should still be ID/reported because they are potential pathogens
In what environment are many opportunistic fungal pathogens acquired?
Construction, demolition, or remodeling of buildings through inhalation or they are hospital acquired
Which organisms are in the Mucorales family? (6)
- Rhizopus sp.
- Mucor sp.
- Lichtheimia sp.
- Rhizomucor sp.
- Cunninghamella sp.
- Syncephalastrum sp.
Which organism are the opportunistic Hyaline Molds? (6)
- Penicillium sp.
- Aspergillius sp.
- Fusarium sp.
- Scopulariopsis sp.
- Paecilomyces sp.
- Chrysosporium sp.
Which opportunistic fungal pathogen is considered “other” and is not a part of the hyaline or mucorales family?
Pneumocystis jirovecii
The Mucorales family were formerly known as…..?
Zygomycetes
Characteristics for ID of Mucorales Family
- Produce large, ribbonlike hyphae, irregular in diameter, contain occasional septa
- Have sporangia and sporangiospores
What are sporangia? Sporangiospores?
Sporangia - large, saclike fruiting structures that release sporangiospores (spherical, yellow/brown)
**Be able to label these on a diagram probably
What is a sporangiophore?
A supporting structure for the sporangium
**Be able to label these on a diagram probably
What is a stolon?
Occasional septate hyphae that connect sporangiophores
**Be able to label these on a diagram probably
What is a Rhizoid?
Root-like structures that spread from stolons
Presence or absence is helpful in ID to different Mucorales family
**Be able to label these on a diagram probably
Mucorales family typically only causes disease in immunocompromised patients. What SPECIFIC patients do these fungi typically have a higher chance of infecting?
Diabetes Mellitus patients due to decreased pH and sugary blood
How are Mucorales family fungi acquired?
Through inhalation of spores or percutaneously
What disease does Mucorales family cause?
Mucormycosis, marked with rapid vascular invasion so they rapidly produce thrombosis and necrotizing tissue
What is the rhinocerebral form of Mucormycosis?
Vascular invasion of specifically the nasal mucosa, palate, sinuses, orbit, face, and brain
Special specimen transport of Mucorales
Must be transported within 2 hrs to the lab, b/c Mucorales are extremely sensitive to environmental changes
Special characteristics to ID Mucorales microscopically
Under calcofluor/KOH prep, Mucorales have branching, broad-diameter, predominantly nonseptate hyphae
Special characteristics of Mucorales colony growth
Fluffy, white to gray to brown hyphal growth resembling cotton candy
Considered lid lifters because hyphae can grow very fast and lift agar plate lid
What is apophysis?
Swelling of the sporangiophore below the columellae
What is columella?
The central axis of the sporangia
Slide 14 has an image of labeling structures of Mucorales fungi, probably should know it
If only I could insert a photo without PAYING
Mucor morphology is slightly different than other species in the Mucorales family…. how?!
NO rhizoids or stolons present in microscopic morphology!
What is standout about Lichtheimia microscopic morphology?
Pyriform sporangia with a funnel-shaped apophysis
What is among the most COMMONLY encountered fungi in the clinical laboratory??
Aspergillus species
Describe the disease that Aspergillus species causes
Aspergillosis
Pulmonary or sinus fungus balls (aspergilloma)
External otomycosis (fungus ball of external auditory canal)
Onychomycosis (infection of nail/ned bed)
Most commonly a primary pulmonary infection that disseminates
What is standout about Aspergillus fumigatus characteristic?
THERMOTOLERANT –> can withstand temperatures up to 45C
What is standout about Aspergillus fumigatus microscopic morphology?
Conidiophores have a T/L shaped “foot cell” at their base
Tip of conidiophores have bottle-shaped phialides that cover upper half of its surface only
What is standout about Aspergillus flavus colony morphology??
It is yellow/green! (Hence, flavi = yellow)
What is standout about Aspergillus flavus microscopic morphology?
Globose vesicles
Phialides can either be UNISERATE –> produced directly from the vesicle surface
OR BISERATE –> produced from a primary row of cells called metulae
What is standout about Aspergillus niger colony morphology?
Begins as a yellow colony, soon develops black dotted colony, and eventually turns jet black and powdery
What is standout about Aspergillus niger microscopic morphology?
Biserate phialides
ENTIRE surface of vesicle is covered
These look like dandelions :)
What are the 2 most commonly isolated Fusarium species?
- most common - Fusarium solani complex
- Fusarium oxysporum complex
What is the disease of Fusarium sp. like?
Causes mycotic keratitis after traumatic implantation
Disseminated fusariosis commonly accompanied by fungemia
Describe the microscopic morphology of Fusarium sp
Microconidia –> borne in gelatinous heads (whatever TF that means)
Macroconidia –> large, sickle/boat shaped contain numerous septations
Most Penicillium species are considered ____________, but ___________ is the only species considered a true fungal pathogen rather than an opportunistic organism.
Contaminants; Talaromyces marneffei (formerly Penicillium marneffei)
Describe the microscopic morphology of Penicillium species
“Brushlike conidiophores”
Conidiophores produce metulae, phialides arise from metulae, chains of conidia
(looks like fingers or a mop)
Describe the microscopic morphology of Scopulariopsis sp.
Annellophores produce produce flask shaped annelides which support lemon-shaped conidia in chains
Conidia are large, have a flat base, and are rough-walled
What is the microscopic morphology of Paecilomyces like?
Long, delicate, tapering phialides
Chains of small, oval conidia are easily dislodged
What is the causitive agent of Pneumocystis?
Pneumocystis jirovecii
What is PCP?
Pneumocystis pneumonia; associated with P. jirovecii
P. jirovecii was originally thought to be a ________, not a fungi. Why?
Trypanosome.
Due to similar morphology to a protozoa and this organism responds to antiprotozoal drugs, NOT antifungals
What are the 3 life cycle stages of P. jirovecii? What is the diagnostic form?
- Trophic form (trophozoite)
- Sporozoite (precyst)
- Ascus (cyst) –> diagnostic form
How does P. jirovecii differ from other fungi?
- Cell membrane contains cholesterol, not ergosterol
- Only 1-2 copies of small ribosomal subunit gene
Describe the epidemiology of P. jirovecii (disease manifestation, notable fact, transmission)
Most commonly presents as pneumonia
The most common opportunistic infection among those with HIV/AIDS in the U.S.
Transmits person to person via airborne particles
What is the disease process of P. jirovecii?
Inhalation
Trophic form adheres to pneumocytes (cells of lungs)
Replicate intracellularly, filling alveolar space with eosinophilic foamy material
Infection leads to hypoxemia, cough, fever, etc.
What type of specimen is the best for detection of P. jirovecii?
BAL, sputum
Biopsy of infected organ if extrapulmonary cysts
What is the diagnostic form of P. jirovecii, vs what is the predominant morphology? Explain.
Cyst form is the diagnostic stage because they are more easily distinguishable (contain intracystic bodies)
Predominant morphology is the trophic form, but very hard to visualize.
What is another way, other than microscopic morphology, that P. jirovecii can be diagnosed?
Direct detection of (1,3)-beta-D-glucan
Secretes it in larger amounts than other fungi
