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Fungus Flashcards

0
Q

Fungal cell wall

A

Membrane - ergosterol instead of cholesterol
(target of amphotericin)
Cell wall - unrelated to bacteria
- lots of cell mass, 90% polysaccharides
- inner - glucan and chitin - glycosilidic cross-link -> stability
- glucan also allows expansion and contraction (middle layer)
- glucan is key antigen for immune response
- outer - glycoproteins

Capsule - Cryptococcus only
- glucuronoxylomannan (GXM) polysacc -> shed during infection

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1
Q

Overview of fungi

A

Kingdom within eukaryotes (have nuclear membrane)

  • > 3 Phyla -> 3 medical genera (by sexual structure)
  • Ascomycota (asci contain ascospores)
  • largest, most diverse -> Aspergillus, Candida, (Saccharomyces, Neurospora)
  • Basidiomycota (basidium) - Cryptococcus neoformans
  • Zygomycota (zygosporangium) - Mucos sp.

Non-motile (medically-important)
Digest food externally -> absorb
Both sexual and asexual reproduction
Limited anti-fungal rx dt similarities with mammalian cells

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2
Q

Antifungal overview

A

Fewer targets due to similarities with mammalian cells

Azoles -> p450 enzymes - ergosterol synthesis
Polyenes -> ergosterol
Echinocandins -> beta glucan synthesis

Resistance - usually genomic vs acquired elements

  • increased expression
  • alteration of targets
  • can have high mutation rates (-> use multiple agents)
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3
Q

Polyene antifungals

A

Bind to sterols -> disrupt membrane permeability
- greater affinity for ergosterol (fungi) vs cholesterol (host)
Poorly absorbed from GI
High toxicity

Amphotericin B - used systemically but toxic, fungicidal
Nystatin - only used topically or oral (not absorbed)
- only fungistatic at attainable concentrations

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4
Q

Azoles antifungals

A

Target p450 enzyme for ergosterol synthesis

  • > weird steroids in cell membrane
  • > inhibit membrane/hyphae growth (static)
  • also more susceptible to phagocytosis

Oral, systemic but hepatotoxicity in 0.01%
Thrush, systemic, chronic (ex AIDS)
Fluconazole, ketoconazole

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5
Q

Echinocandins

A

Inhibit synthesis of cell wall
- beta glucan synthase
- cidal
Caspofungin

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6
Q

Antimetabolite antifungals

A

Flucytosine
Uracil -> 5F-uracil -> inhibits protein synthesis
Thymidine -> 5F-deoxyuracil -> inhibits DNA synthesis

Can be cidal or static depending on organism

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7
Q

Overview of fungal growth

A

Exogenous (free-living) vs
Endogenous (must be in human or animal)
- ex Candida in GI

Absorptive heterotrophs - secrete enzymes, absorb smaller compounds

Acid tolerant (grow optimally at pH s agar

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8
Q

Secondary metabolites

A

Synthesized by non-ribosomal polypeptide or polyketide synthase
NOT necessary for fungal growth

Beneficial:
- lovastatin from Aspergillus
- equisetin (anti-viral) from Fusarium
- penicillin from Penicillium
Aflatoxins - produced by Aspergillus, Fusarium
- grain or peanuts contaminated
- mycotoxicoses, carcinogens (low amounts needed)

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9
Q

Yeast

A

One of two main forms (vs hyphae - different organisms)

Oval cell
Division = budding/fission
apical -> pinches off cell and nuclear membranes
Smooth pasty colonies

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10
Q

Hyphae

A

Elongated filament

Septa -> mononuclear segments
 - vs aseptate/coenocytic (division and growth without fission)
Growth - exclusively apical
 - Spitzenkorper = special vesicles near tip
 - can extend into new substrate
  - penetrating due to turgor pressure
  - release polymer degrading enzymes
 - can be rapid (40 microns/s)
 - can also grow aerial -> spores
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11
Q

Spores

A

Reproductive propagule
- conidia = asexual - either micro (airborne) or macro (-> ID)
- arthrospore - fragmentation of hyphae
Usually form from aerial hyphae
- hyphae + spores = mycelium
Can be small (1 micron) -> lower respiratory

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12
Q

Overview of yeast growth

A

Often dimorphic - both yeast and hyphal depending on env’t
- elongated yeast = pseudohyphae = intermediate form
- beginning of hyphae from yeast = germ tube
Classical thermal
- soil (low temp) -> filamentous hyphae -> conidia
- body temp -> yeast
- unnatural, “dead-end” env’t (no spore production)
Candida albicans
- soil -> yeast; body -> hyphae
- find yeast, hyphae and pseudohyphae in infected tissue

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13
Q

Cutaneous mycoses pathogenesis

A

Dermatophytes - keratinase -> nutrient source
- filamentous septate hyphae
- invade hair from inside (endothrix) or outside (ectothrix)
-> produce micro and macroconidia
Epidermophyton
Trichophyton - anthrophilic - human-> human via skin fragments
Microsporum - zoophilic - pets
- fluoresces in UV light

Non-dermatophytes - some dimorphic
Cladosporium - geophilic - soil (dimorphic!)

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14
Q

Cutaneous mycoses clinical

A

Most common fungal infections (25% prevalence)

Dermatophytes -> tinea (ex capitus, pedis, cruris)
Tinea versicolor
- Malassezia furfur (normal flora) -> dandruff, hypopigmented
- dimorphic yeast and hyphae
- lipophilic, can be in blood if IV lipids
Tinea nigra - Cladosporium werneckii -> produces melanin

Dx: skin scrape -> KOH mount with Calcofluor
- can do culture (Sabourad’s) -> microscopy
Tx: topical antifungal (azole)
- oral azole, terbinafine, griseofulvin
- ciclopirox/Penlac for nails
- limit moisture, may need ID

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15
Q

Subcutaneous mycoses

A

Rare!
Puncture or abrasion -> contamination with soil fungus

Sporotrichosis:
- Sporothrix shenkii - classical dimorphism (“cigar” yeast at 37C)
- puncture -> nodules (-> disseminated if immune compromise)
Chromoblastomycoses
- dematiaceous (multiple soil species) - produce melanin
- puncture -> wart-like crusty lesion with brown cells
- mycetoma - abcess with pus -> requires surgery

Dx: KOH mount, biopsy
Tx: oral azole or flucytosine
Prevention - protective clothing

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16
Q

Overview of fungal infections

A

Cutaneous -> keratinized skin, nails, hair
- direct contact -> inflammatory rx
Subcutaneous - trauma -> dermis, fascia, etc
Systemic - blood or organs, from GI, resp
Opportunistic - invasive in immune compromised

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17
Q

Candida epidemiology

A

Normal colonizer of oral, vagina, GI (from birth)
- DTH skin test (+) in all immunocompetent

Infections - common invasive life-threatening
- most common fungal BSI, 4th most common nosocomial BSI
- immunocompromised (liver transplant)
- invasive procedures (GI surgery, catheters)
- ICU (trauma, NICU)
Almost all are Candida albicans
400K/yr worldwide, most in developed

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18
Q

Candida pathogenesis

A

Source: normal endogenous (or nosocomial in ICU)

Non-classical dimorphism (polymorphic) - all forms found in tissue
Yeast - normal room temp
- overgrow if immunocompromised (esp cellular), antibiotics
-> germ tubes -> vegetative/invasive hyphae
-> also pseudohyphae
Hyphae
- vegetative - form on or below agar (NOT aerial)
- adhesins vs keratinocytes ->
- invasion -> white punctate lesions -> thrush/pseudomembrane
(usually limited to upper epithelial layers)
-> yeast spread to new sites (also stress resistant)
Bloodstream if heavy skin colonization, immune compromise
- or biofilm on catheter -> yeast

19
Q

Candida clinical syndromes

A

Normal hosts:
- vaginitis common
- diaper rash (moist areas)
- oral erythema
Immunocompromised
- oral thrush - infants, HIV, chemo (poor cellular immunity), dry mouth
(one of earliest, most common after HIV)
-> pain, dysphagia, susceptibility to other infections
- esophageal - leukemia, lymphoma, suppressed - serious

20
Q

Candida species

A

C albicans - most common (50-60%)
- positive rapid germ tube test (1 hour in 37C)
C glabrata - second most common
- normal commensal, also only in mammal hosts (not env’t)
- more resistant to azoles, amphotericin
- no germ tubes or pseudohyphae
- 15% of infections worldwide
C tropicalis, parapsilosis
- negative rapid germ tube, positive pseudohyphae
- similar presentation to albicans

21
Q

Candida diagnosis

A

Mucous, skin
-> tissue - KOH mount, PAS, GMS
-> culture (blood, Sabourad’s) -> smooth white colonies
Deep/blood infections - difficult
- blood cultures (Wright’s) may be negative
- new molecular methods -> higher sensitivity?

Identification

  • rapid germ tube - (+) for albicans
  • chlamydospores on special media - not normally performed
  • definitive = fermentation, assimilation of carbon sources
22
Q

Candida treatment

A

Oral - prevent with nystatin, azole rinses etc
- tx with fluconazole, caspofungin (inc esophageal)
Vaginitis - topical azoles, fluconazole
Disseminated - use scoring system/algorithm
- usually fluconazole
- echinocandins, azoles, amphotericin

23
Q

Immunity to fungi

A

Innate = essential!
- non-inducible (skin, microbiome)
- recognition via PAMP, lectin receptors
(cell wall beta glucan vs dectin-1 receptor)
- neutrophils
- macrophages
Adaptive
- mostly CD4 -> Th1 -> IFN-g -> macrophage -> granulomatous response -> can have reactivation
- some Th17 -> recruit neutrophils, induce epithelial protection at mucosal surfaces
- antibodies present but unclear fx

24
Overview of fungal dx
Histology - KOH or NaOH - disolves tissue, leaves fungi intact (dt carbs) - PAS, methanamine silver - india ink -> Cryptococcus capsule Culture - may be dangerous due to spores! - yeast -> 48 hours -> differential media - molds - slower, may be negative -> wet mount with lactophenol cotton blue to ID spores - pathogens can grow at 37C!! DNA probes Serology
25
Immune susceptibility to fungal
Helps determine likely/posible pathogens Breach of non-inducible - microbiome (antibx), catheters Can be receptor, signalling, recruitment, effector Receptor - ex dectin-1 polymorphism -> Aspergillus Effector - esp neutrophils, macrophages - CD4 -> Th1 -> IL12, IFNg, TNFa = essential - also CD8, Th2, Th17, Treg -> length/severity Ex: Immune reconstitution inflammatory syndrome (IRIS) -> increase in CD4 vs established pathogens (Cryptococcus, Pneumocystis jirovecii)
26
Fungal pre-dispositions
Neutropenia -> Candida, Aspergillus, Mucormycoses, Trichosporon, Scedosporium, Fusarium T-cell (HIV) -> Cryptococcus, Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, P marneffi, dermatophytes, Candida Skin/mucosal trauma - Candida, Aspergillus, Fusarium Chronic granulomatous - Aspergillus, Candida (disseminated) TNFa inhibitors - Aspergillus, Histoplasma Graft vs host - Aspergillus Ketoacidosis, Deferoxamide - Mucormycoses
27
Overview of endemic fungal pathogens
Inherent/primary pathogens! (do not need immune compromise) Geography - restricted region! - 3-24,000 deaths/yr in US, mortality 1-75% Exposure - inhalation of spores, rarely human-human -> dimorphism (yeast at 37C) - lab cultures can be dangerous Immune = cell-mediated -> macrophage -> granuloma - latency within granuloma - disseminates in immune compromise - much more severe in HIV+ - skin DTH to determine exposure - highly varialble - can be short assymptomatic -> latent, lethal ``` Coccidiodes Histoplasma Blastomyces Paracoccidiodes Penicillium marneffei ```
28
Coccidiodes mycology
C immitis, posadasii Barrel arthroconidia (2-6 micron) -> fragment -> airborne - within alveoli -> large spherules (12-100 micron) -> rupture -> release endospores -> new spherules 150K cases annually in US southern CA, Arizona -> central Texas (dry, hot, alkaline) - reportable, 2/3 cases in AZ
29
Coccidiodes presentation
Macrophages -> neutrophils (resistant to neutro) -> Cell mediated immunity = protective - 2-4 weeks, DTH (+) Often asymptomatic - more sx in dark-skinned men (ex Filipino) Pulmonary - 40% lower resp (sputum, CP, fever, anorexia) - 2-6 weeks - "Valley Fever" Erythema nodosum (EN) - 10% - non-septic nodules in lung - indicate protective immunity (not disseminated) Rare - disseminated (usu defective cellular immunity) -> granulomatous skin lesions, osteolytic, meningitis - more common in third trimester
30
Coccidiodes dx and tx
tissue -> KOH or stains -> spherules Sabourad's culture -> dimorphism, tissue form - hazardous!! Serology - IgM (2-4 weeks) -> IgG - proportional to current burden (increase if disseminated) Primary - no tx needed Disseminated - azoles, amphotericin
31
Histoplasma mycology and pathogenesis
Branching septate hyphae -> - tuberculate macroconidia (ID) - microconidia -> inhaled -2-3d> ovoid yeast - > intracellular growth within macrophages - > migrate widely to nodes, spleen, liver - 9-15d> cell-mediated immune response Virulence = growth within macrophages - produces bicarb, ammonia -> raises pH of phagosome Can have extracellular yeast, infect epithelial cells
32
Histoplasmosis presentation (and geo)
Widely distributed Ohio and Mississippi River Valleys (up to 90% DTH +) Most assymptomatic Acute pulmonary - self-limited, flu-like - anatomic abnormalities -> colonize pulmonary recesses Opportunistic -> chronic - similar to TB
33
Histoplasma dx
Disseminated - blood (Wright's) + for intracellular yeast Tissue stain Culture on special media -> dimorphic with tubercular macroconidia Antigen in urine Serology - decreases when inactive - cross-reacts with Blastomyces Skin test only used for epi (disrupts serology)
34
Blastomyces mycology and geography
Mold -> pear conidia -> Characteristic yeast (= diagnosis via KOH, stain) - thick-walled, large with broad based single bud Geography - similar to Histo? skin test cross-reacts... - Ohio and Mississippi rivers, Carolinas - recreation along wooded waterways Clinical disease is more common Dogs susceptible in endemic zones - frequently severe/lethal
35
Blastomyces pathogenesis
Conidia -> inhalation -> yeast -> multiply -> disseminate via macrophages, blood, lymph Bad1 = virulence - promotes uptake by macrophages -> replicate and travel until activated by T cells - homology with invasin of Gram (-) Immunity - several weeks -> T cells, Ig, DTH+ -> protective Presentation: Asymptomatic or flu-like Disseminates -> organs (not uncommon) - can have 60% mortality Trophic for skin, bone -> ulcerative lesions
36
Paracoccidioidis
South America - forested, tropical, armadillo nests Most common men (coffee plantation) Large yeast with multiple blastoconidia -> "pilot wheel" Often chronic, subclinical with latent periods primary pulmonary -> mucosal lesions (50%) -> cutaneous (25%)
37
Penicillium marneffei
Only thermally dimorphic (pathogenic) Penicillium SE Asia - 3rd most common infection with HIV regionally Pulmonary -> disseminated -> often fatal
38
Overview of opportunistic fungi
Geographically widespread Almost always affect immunocompromised - 100% lethal if untreated (still high if treated) Grow well at 37C ``` 90% of disease from 4 genera: Cryptococcus Aspergillus Mucor Pneumocystis ```
39
Cryptococcus epidemiology
Almost all cases associated with AIDS or other compromise Most life threatening infections of any fungus - most meningo-encephalitis Est 1 million worldwide - 620K deaths/yr in sub-Saharan - mortality rate 15-20% US treated, 55-70% South America, Africa C neoformans - widespread in soil, pigeon shit -> compromised - 2 different serotypes C gatti - trees, Canada -> Pacific NW - both compromised and healthy
40
Cryptococcus pathogenesis
Basidiomycetes - grows as yeast in agar and tissue - urease (+), grows well at 37C -> inhalation of spores or dessicated yeast Capsule - glucuronoxylomannan (GXM) - essential for virulence - extracellular - protects within phagolysosome -> ID via India Ink stain Phenol oxidases - DA -> melanin - protects from oxidative damage Lungs -> systemic -> preferential to CNS -> meningo-enceph - either microcapillaries -> BBB or via macrophages
41
Cryptococcus clinical
Meningo-encephalitis most common - insidious onset -> h/a, stiff neck after high fungal burden Pulmonary -> cough, SOB, encapsulated nodules Subclinical urinary, resp Dx: Capsule antigen in urine, plasma, CSF = definitive - latex agglutination assay Can visualize capsule - India ink, mucicarmine, PAS, methanamine - less sensitive and specific than antigen Culture - CGB agar: gatti turns yellow -> blue vs neoformans - bird seed culture, L-dopa
42
Aspergillosis mycology and pathogenesis
A flavus, fumigatus (most common), terreus (resistant) - only hyphae, not dimorphic Hyphae - septate, aerial -> conidiophore -> brush conidiospore -> Airborne -> germ tubes -> colonize cavities -> septate, branched Often fills cavities from trauma, TB, etc Penetrating -> disseminated Requires immediate and aggressive antifungal therapy Ubiquitous -> 200K infections/yr
43
Aspergillosis clinical presentations
Immune compromise -> invasive (acute) or chronic - neutrophils, organ transplant, steroids, COPD -> fever, cough, CP, etc - aspergilloma - "fungus ball" - fills cavity from TB, trauma - dx via hyphal morphology - serum test for galactomannan - only sensitive if neutropenic without antifungal therapy Allergic bronchopulm Asp - ABPA - - A fumigatus -> Th2 mediated disease - prevalence 20% CF, 5-15% asthma - dx via eosinophilia, IgE
44
Mucormyces
Zygomycetes - Mucor, Rhizopus - many similarities to Aspergillus - hyphae/mycelium only, not dimorphic - BUT not septate -> coenocytic with sporangiophores - right angle branching, "folded" - faster, more virulent than Asp -> increasing Rhinocerebral (50%): DKA -> rhino -> sinus -> cerebral Pulmonary: most in hematologic, neutropenic Deferoxamine therapy predisposes Other sx: cutaneous, pulmonary, disseminated Difficult to isolate/ID organism - half are Rhizopus Growing resistance dt azole prophylaxis therapy 10K infections/yr
45
Pneumocystis mycology
Specific species for each mammal host - co-evolution C jiroveci = human - CANNOT BE CULTURED - ubiquitous (70% Ig +) -> 400K cases/yr Cyst -> rupture -> sporozoites -> pleiomorphic trophozoite ? Is it a parasite? - morphology similar to Apicomplexa - susceptible to pentamidine, not amphotericin - cholesterol vs ergosterol in membrane Evidence for fungus: - DNA, elongation factors - thymidylate synthase, dihydrofolate reductase (diploid) - cell wall = chitin, glucan, mannoproteins
46
Pneumocystis clinical
Susceptibility - low CD4 (AIDS, inflammation -> plasma cells -> Ig -> frothy exudate - diffuse interstitial pneumonia -> impaired O2 exchange - sudden onset, high mortality Dx: methanamine silver or fluorescent specific antibodies - PCR may be useful Tx: does not respond to classic antifungals

Microbiology (23 decks)

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