Intro to Clinical Mycology Flashcards
Saprophytes
Plant, fungus, or microorganism that lives on dead or decaying matter
Commensal vs Symbiotic vs Parasitic
C: no benefit or harm to us
S: mutually beneficial
P: cause disease in us
Examples of Mycotoxins
Ergot Alkaloids (Salem Witch Trials; women having psychotic episodes due to consumption of ergot alkaloids via bread)
Aflatoxin (Peanuts)
Stachybotrys (Black mold in houses)
Recreation “shrooms”
What are the two important differences/targets that fungal cells possess compared to humans?
Cell wall and Membrane sterol composition (have ERGOSTEROL rather than cholesterol)
What type of pathogenic yeast possess a capsule?
Cryptococcus neoformans
Most of our immunologic response is due to ____
Cell wall
Fungal Cell Wall Function
-Shape, rigidity, strength, protection from osmotic shock
***~90% of cell mass is cell wall
Fungal Cell Wall Composition: Polymer vs Monomer
Polymer: Chitin, Chitosan, Cellulose, a-Glucan, B-Glucan, Mannan
Monomer: N-acetyl glucosamine, D-Glucosamine, D-Glucose, D-Glucose, D-Mannose
*** = bolded on slide
Cell wall also contains proteins (mannoproteins)
Fungal Cell Membrane (Function, Structure)
F: Regulate nutrient flow, contains cytoplasm
S: Typical phospholipid bilayer, Unique sterol composition (Humans = cholesterol, Fungi = ERGOSTEROL)
Fungal Structures and Classification
Yeast (e.g. Candida)
Molds
Both (called DIMORPHIC when they can grow as both; e.g. molds in bat droppings transform into yeast in the body of humans)
Yeast (Morphology and Reproduction)
M: Unicellular; spherical or ellipsoid
R: Budding
What type of yeast produces a germ tube?
Candida albicans
Blastoconidia
Bud
Pseudohyphae
Chains of elongated buds; look like hyphage in bacteria
Germ Tube
Looks like SPOON; yeast send out a SINGLE long narrow extension (“bud gone wrong”)
99% of the time will be Candida albicans
Mold Characteristics (2 of them)
- Hyphae (i.e. Mycelium): can be vegetative (grow into substrate) or aerial (grow into air)
- Septa (Septum): septa or aspetate (coenocytic)
Mold Reproduction
Both Asexual (via Conidia) and Sexual (via Spores)
***Conidia and Spores will be used interchangeably
Mold: Asexual Reproduction
Via Conidia
-Can be either Micro-, Macro-, or Chlamydo- (Arthro-)
Chlamydo/Arthro = conidia right within the strand of a hyphae
Fungal infections are diagnosed ____
Visually; there are not a lot of biochemical tests that can be done for them
Superficial Mycoses
Infections of the outermost layers of skin and hair
e.g. Pityriasis versicolor, Tinea nigra, Black and White Piedra
“These are more COLONIZATIONS than infections”
Cutaneous Mycoses
Infection which extends deep into the epidermis as well as invasive hair and nail infections
e.g. Dermatophyte infections- Ringworm, Athlete’s Foot, Jock Itch
***Most common fungal infections
Subcutaneous Mycoses
Infections involving the dermis, subcutaneous tissues, muscle, and fascia
e.g. Sporotrichosis, Chromoblastomycosis
Systemic Mycoses
Infections that originate in the LUNG but may be spread to any organ in the body
e.g. DIMORPHIC fungi: Histoplasmosis, Blastomycosis, Paracoccidioidomycosis, Coccidioidomycosis. Yeast: Cryptococcosis
***All acquired initially by INHALATION
Opportunistic Mycoses
Infection associated primarily with immunosuppressed individuals
e.g. Candidiasis, Aspergillosis, Zygomycosis, Pneumocystis carinii pneumonia
____ Immune System is generally sufficient to prevent fungal infections in healthy individuals
Innate
Who are at risk for fungal infections?
Burn patients, immunocompromised patients, patients who are constantly exposed to fungal spores
How else can fungi gain access to host tissues?
Traumatic implantation (e.g. rose bush thorns, sporotrachosis, cuts on the feet) or inhalation
The severity of disease caused by fungi depends upon the size of the _____, magnitude of _______, the ability of fungi to ________, and the ______ of the host.
Inoculum, Tissue Destruction, Multiply in tissues, Immunologic status
What is most effective at controlling and eliminating fungal infection: Humoral (antibody) or Cell-Mediated Immunity?
Cell-Mediated (becomes compromised with Immunosuppression - steroids or radiation, AIDS, T-cell and neutrophil deficits)
Main concern with antifungal drugs
Crossover in toxicity to the host due to lack of unique features
Topical Therapy
Used for superficial/cutaneous infections
Systemic Therapy
Used for subcutaneous and systemic infections, some cutaneous
What are the most common targets of Antifungals?
Cell wall and Cell membrane
What two parts of cell wall synthesis are inhibited?
Glucan synthesis (by Echinocandins)
Chitin synthesis (by Nikkomycin)
What part of cell membrane synthesis are inhibited?
Ergosterol synthesis (by Azoles and Allylamines)
How do Polyenes act as Antifungals?
Bind to Ergosterol and disrupt fungal cell membrane
What drugs inhibit Ergosterol synthesis?
Azoles, Allylamines, Thiocarbamates, Morpholines
Mnemonic: “A lil ATM” –> Allyl ATM
What drug binds directly to Ergosterol?
Polyenes
Amphotericin B (Agent and Mechanism)
A: Polyene***
M: Binds to ergosterol in the membrane, causing a PORE to form, leading to osmotic disruption/leakage/influx of fluid into cell
*** = Definitely know this
Echinocandins (e.g. caspofungin, anidulafungin, micafungin)
- Cell wall synthesis inhibitor*
- Inhibits B-glucan synthesis (via 1,3-B-D-glucan synthase) and is only effective against fungi that use a lot of B-glucan in their cell wall synthesis
e. g. Candida and Aspergillus
Laboratory Diagnosis of Fungal Infections
Diagnosis of fungal infections is frequently made by DIRECT VISUALIZATION OF FUNGAL ELEMENTS in infected tissues
KOH Preparation
Used to examine hair, nails, skin scrapings, fluids, exudates, or biopsies
Dissolves away nails, skin, hair, etc at a greater rate than fungal structures to allow visualization of fungal structures (i.e. hyphae, large yeast, spherules, and sporangia)
All dyes tend to bind _____
Carbohydrate-rich cell wall (e.g. Chlorazol Black, Calcofluor White)
Tissue sections/Histological specimens may also use specialized stains to enhance detection of fungi (e.g. Gomori methlamine silver (GMS) and Periodic acid-Schiff (PAS))
All fungi stain ____
Gram Positive
When you see an India Ink Stain, think
Cryptococcus neoformans
Germ Tube Test
Used to identify Candida albicans
-Serum is mixed with sample for a couple of hours, and if germ tubes form, then you know it is Candida albicans
Examples of Fungal Lab Cultures
Sabouaud’s dextrose agar
Cornmeal agar
Czapek Dox agar
