Intro to mycology

Question 1

What is a fungus? Categories?

Answer 1

Eukaryotic kingdom. Few that cause disease. Larger than bacteria. Heterotroph, require preformed organic carbon. Mushrooms, yeast, mould

Question 2

Structural features

Answer 2

Chitin: Cell wall polysaccharide (mannan and glucan too), Distinguishes fungi from plant cells (cellulose), Adsorbs certain dyes, key identification feature; No cell wall in mammalian cells; Peptidoglycan is polymer in bacterial cell wall. Ergosterol: Cell membrane sterol (rigidity, Distinguishes fungi from mammalian cells (cholesterol) – Antifungal target

Question 3

Yeast general

Answer 3

Unicellular, round/ovoid, asexual budding. Yeast are normal GI flora. Genus of note is candida, cryptococcus, malassezia. Microscopy look different, look for structure. Plated cultures hard to tell apart from bac.

Question 4

Mould general

Answer 4

Filamentous fungi, multicellular, filamentous, branching growth. Hyphae/mecelia, growth at the hyphal tip -reproduce primarily by conidia: asweual spores, give mould its colour, easily airborne (transmit, allergy, etc). Humans have no endogenous mould. Microscopy look like dandelion. Plates look fuzzy.

Question 5

Superficial fungal diseases

Answer 5

aka cutaneous. The Dermatophytes have tropism for keratinized tissue – skin, hair, and nails; rarely invade deeper tissues. Athletes foot, ringworm

Question 6

Subcutaneous fungal diseases

Answer 6

Deep, ulcerated skin lesions. Nodules pop up. Rarely invade deeper tissues. Sporotrichosis (Sporothrix). Not many of these.

Question 7

Opportunistic fungal diseases

Answer 7

Not ‘true pathogens’, low virulence potential, Require immune compromise. ex. Aspergillus, Candida, Mucor, Cryptococcus

Question 8

Endemic fungal diseases

Answer 8

aka. Systemic/Dimorphic. ‘True pathogens’, cause severe disease in healthy people. Restricted geographically. Usually involve lungs, as well as deep organs via dissemination. ex. Histoplasma, Blastomyces, Coccidioides

Question 9

Human/fungi interaction.

Answer 9

Limited. Most like 25-30C and slightly acidic pH. Innate immunity prevents most growth unless you have deficiencies etc.

Question 10

Transmission methods of fungi

Answer 10

Inhalation — spores, conidia; Aspergillus, Endemic mycoses. Mucosal colonization – Candida. Skin break or injury – Candida, Sporothrix

Question 11

Immune regonition of fungi

Answer 11

Opsonins (comp, AB), PRR, TLR bind fungi. Activate phagocytosis, cytokines, resulting in ingestion or extracellular phagocyte killing

Question 12

Risk factors for invasive mycoses

Answer 12

Immunosuppression (Chemotherapy). Promotion of fungal colonization – Antimicrobial therapy. Direct access to blood, lungs, deep tissues – catheters, chemotherapy, Solid organ transplantation, Travel

Question 13

Patients at high risk for invasive fungal infection (IFI)

Answer 13

HSCT (blood stem cell recipient) - depends on how bad; SOT (solid organ transplant) - may depend on type of organ

Question 14

Diagnosing fungal disease

Answer 14

Specimen quality is very important. bronchial washing. Tissue or aspirate in sterile container. Not a lesion swab, sputum, stool (too much else going on). Microscopy (gram, silver) tells whether mould or yeast. Culture (yeast is smooth, round; and mould is fuzzy, filaments). Serology

Question 15

Pros of microscopy

Answer 15

Quick (same day), see unique cell features, some are quickly identified

Question 16

Pros and cons of culturing fungi

Answer 16

Confirms ID, usually unique features. Culture isn’t always positive, and it is slower (several days)

Question 17

Antigen detection for fungi

Answer 17

Some assays for antigens, but fairly limited.

Question 18

Serology for fungi

Answer 18

Look for AB, but usually there aren’t many. They general dono’t generate humoral response.

Question 19

Antifungal classes

Answer 19

Polyenes, azoles (targets cell membrane) , enchinocandins (targets cell wall), nucleoside analog

Question 20

Antifungal susceptibility testing

Answer 20

Test with broth microdilution (look at MIC); and disk diffusion (zone of inhibition). Determines if that anti fungal will be good or if they have resistance.

Question 21

Pulmonary Invasive aspergillosis

Answer 21

Mortality 50-100%. Persistent. Thermotolerant. Not responsive to antibiotics. Shows up at halo in lung. Can disseminate throughout bloodstream if they break out of alveoli.