Microbiology

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CRYPTOCOCCUS NEOFORMANS

clinical significance:

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important opp.path. in AIDS, an "AIDS defining illness"

Requires life-long therapy

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Structure:

Location:

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ONLY pathogenic fungus with a capsule

First ID'd in peach juice, major contaminants = soil contam with pigeon droppings, eukalyptus trees, decaying wood-forming hollows in living trees

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Growth form:

Staining:

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Yeast (in agar and clinical specimens)

Stains poorly with gram and others, requires special fungal stain

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Virulence factors:

Growth Characteristics:

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1) MAJOR one = GXM capsule (glucuronoxylamannan) - 4 serotypes
2) Melanin - has phenol oxidases which use dopamine to create melanin

grows at 37C, Urease +

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Route of transmission:

Most common disease:

Most common disseminated sites:

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Most common = inhaled spores or dessicated yeast forms

chronic meningitis

bone and skin

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Location:

Diagnosis:

Stain:

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world-wide, ubiquitous
associated with bird droppings and vegetation

Detect capsular Ag with latex beads that have anti-capsular Ab's

Capsule stains red with mucicarmine

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Prevention:

Treatment:

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promising research on capsular vaccine (conjugated to tetanus toxoid)

amphotericin B, and flucytosine (synergistic)

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HEMATOGENOUSLY DISSEMINATED DISEASE caused by C. ALBICANS

Clinical significance:

Can lead to what infection?

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hospital bloodstream infections - 4th most common cause

Internal candidiasis of any tissue

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Lab ID:

Treatment

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positive blood cultures = infection BUT may be negative even though abscesses are present on internal organs

Internal infections: Amphotericin B, binds ergosterol
Internal and mucosal infections: Azoles, inhibit ergosterol synth enzymes

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ASPERGILLUS

Clinical significance:

Growth form:

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once established in tissue, organisms spread rapidly and penetrate tissue barriers
High risk for systemic disease - neutropenic and immunosuppressed hospitalized pts

A. fumigatus and flavus grow in mycelial forms only (mold)
Cultures - form septate aerial hyphae, stalk-like conidiophores with easily airborne conidiospores

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Infections

Hypersensitivity pneumonitis:
Secondary Colonization:
Systemic aspergillosis:

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allergic bronchopulmonary reactions to fungal Ags -> respiratory distress

pre-existing cavitary lesions in lungs become colonizes - space filled with sperical intertwined, branching, septate hyphal filaments -> minimal distress except hemoptysis

aggressive invasion of blood vessels and tissues, important risk factor = neutropenia

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Location:

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ubiquitous in environment especially air
Contamination of air conditioner filters may occur
NOT normal human flora, but there may be transient colonization

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Diagnosis:
Treatment:

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Culture bronchial washes, tissue, or sputum
use histological staining look for - septate hyphae branching at regular intervals, oriented in same direction, acute angle branching

Amphotericin B

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Other mycelial form opportunistic fungi:

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Zygomycetes (coenocytic, not septate) causes zygomycoses
Mucor causes Mucormycosis
Pneumocystis causes Phycomycosis

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Pneumocystis carinii
aka:

Clinical significance:

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P. jiroveci (new name)

common with AIDS pt's CD4 count < 200 cells/mm3
subclinical pulmonary infections occur worldwide in animals (but each animal has its own type of P. carinii)
Specific antibodies in all children by 4 years

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Culture:

Atypical characteristics for fungi:

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human forms can't be cultured or grown in animals!

1) morphology: similar to phylum Apicomplexa (cysts and trophozoites), relative fragility of cell wall
2) Susceptible to some anti-parasitic agents like pentamidine, trimethoprim/sulfamethoxazole
3) not suscept to Amphotericin B
4) No ergosterol, presence of cholesterol

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Evidence for fungal classification:

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rDNA, presence of EF3 (only in fungi), thymidylate synthase and dihydrofolate reductase on two separate genes (seen in fungi), cell wall chitin, glucan and mannoproteins

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Pathogenesis:

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Forms cysts containing sporozoites, released when cyst ruptures -> mature to trophozoites
Limits Oxygen uptake -> asphyxiation, require oxygen therapy
Interstitial pneumonitis with plasma cell infiltrates and distinctive foamy alveoli

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Transmission:

Prevention:

treatment:

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HIGHLY contageous
Source is unknown, believed to be airborne person to person

keep immunosuppressed pts away from infected pts

antifungal therapy