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72 Cards in this Set

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Most fungal infections in hosptials are opportunistic. What is the causative agent of most of these infections?
C. albicans
Describe opportunistic fungi.
Ubiquitous and low virulence
Mycotic infection is more/less often due to opportunistic fungi in areas with endemic pathogenic dimorphs.
More often opportunistic fungi even in pathogenic endemic areas.
Name some Candida species that are significant human pathogens.
C. albicans
C. glabrata
C. tropicalis
C. parapsilosis
C. kruseii
How does C. albicans reproduce?
It is an oval yeast that reproduces by budding = blastoconidia
What are pseudohyphae?
Buds that fail to detach the mother cell and instead elongate to form pseudohyphae.
What do colonies of C. albicans look like on Sabouraud dextrose agar?
White and creamy after 24-48 hours @ 35.
What is CHROMagar candida?
A selective and differential medium for presumptive identification of Candida species.
What is used in the laboratory to ID C. albicans?
1. Germ tube test - only C. albicans
2. Chlamydoconidia formation - only C. albicans
3. Carb assimilations and fermentations
What is the germ tube test?
Colonies are suspended in bovine serum and incubated @ 35-37 for 2-4 hours.
Look under microscope for primary hyphal elements = parallel sides and non-constricted attachement to primary yeast cell to distinguish from pseudohyphae.
Describe chlamydioconidia formation.
Scratch-inoculate yeast on corn-meal agar and cover with a cover slip; incubate @ 25 for 2-3 days = adverse environment.
Look under microscope for large, thick-walled chlamydioconidia.
"resting conidia"
Why is Candida infection usually of endogenous origin?
Organism is part of the normal GI flora!
--> isolation from mucosa and GI does not always imply infection
--> isolation from normally sterile sites is MORE indicative of infection.
What are two ways Candida infection may occur?
1. Host abnormalities that allow Candida to invade normally sterile tissue
2. Overgrowth in sites where Candida normally exists in controlled sites
What are some common sites of infection with Candida?
Urogenital tract
Oropharynx
Skin
CV system
What are some situations where cutaneous infection with Candida may occur?
1. burns
2. chronic moisture or maceration

** due to breakdown of skin integrity and loss of barrier protection
What is chronic mucocutaneous candidiasis?
Occurs in children with genetic defects in leukocyte function (esp T cell)

Characterized by recurrent severe, debilitating, ulcerative lesions of skin and mucosa

No dissemination to internal organs
What are some predisposing factors for Candida infection?
- Drug therapies - steroids, anti-cancer agents, antibiotics
- Iatrogenic infections - catheter or any foreign body
- Metabolic abnormalities - diabetes, hypoparathyroidism
- Neoplasm - leukemia, lymphoma, neutropenia
- IV drug abuse
What are some virulence factors of C. albicans?
1. Grows at high temperatures
2. Adheres to cell surfaces
3. Produces proteases
What is difficult about diagnosing Candida infection?
Easy to recover Candida in clinical material but assessing the medical significance of a positive culture is difficult.

Direct examination of yeasts and pseudohyphae can be helpful; use PAS, GMS, calcofluor stains
Is serology useful for candida diagnosis?
Serology is also of limited use because Candida is endogenous.

Ab and Ag tests have not been effective.
What is therapy for Candida infections?
Topicals = nystatin, miconazole, clotrimazole

Invasive/disseminated = AmpB, liposomal AmpB, fluconazole, voriconazole
Why are infections due to other species of Candida increasing?
Appears to be rising due to resistance of some of them to fluconazole

C. glabrata, C. kruseii
What kinds of Candida infections are found in IV drug users?
Endocarditis due to C. tropicalis and C. parapsilosis

These species are often found on the skin and are introduced into the bloodstream at sites of inoculation.
What is the major reservoir for C. neoformans?
Pigeons.

Up to 50 million organisms can be found per gram of feces
No disease in pigeons
What is the morphology of C. neoformans?
A yeast that reproduces by single or double buds

**No germ tube or pseudohyphae formation!
What does C. neoformans produce that serves as a virulence factor and is the basis for its serotyping?
Polysaccharide capsule
How is C. neoformans acquired by the human?
Inhalation but primary infection here is usually subclinical
Who has the most life-threatening Cryptococcus infection?
Seen in patients with impaired CMI especially T cells.
Seen in lymphoma and AIDS

#1 cause of fatal fungal infection in AIDS patients
What tissue does C. neoformans have a predilection for?
CNS
How are samples prepared for direct examination of cryptococcus?
1. India ink prep of CSF - LOW sensitivity
2. Histopathological stains of tissue - GMS, PAS, mucicarmine stain (stains capsule)
Can C. neoformans be cultured?
Yes, CSF fluid is specimen of choice, but can also recovered from blood, tissue or respiratory secretions;

Grows smooth, moist colonies on routine fungal media @35
What are four ways to ID C. neoformans?
1. Demonstrate capsule by india ink
2. Production of blastospores only.
3. Urease production - urea agar
4. Pigmented colonies on caffeic acid agar
What is used for serological diagnosis of cryptococcus?
Latex agglutination test to detect cryptococcus polysaccharide in CSF and serum

**more sensitive than India ink
What is therapy for cryptococcus infection?
AmpB +/- 5FC (synergists)

Follow with fluconazole for long term suppression of cryptococcus in AIDS
What are some species of Aspergillus that cause human disease?
A. fumigatus
A. flavus
A. niger
A. terreus (resistant to AmpB!)
What is the morphology of Aspergillus spp.?
Rapidly growing
monomorphic
MOULDS
ubiquitious in most environments
Describe the mycelium of Aspergillus spp.
Septate, hyaline hyphae

Conidiophores have terminal vesicle with phialides that produce chains of conidia

Conidia give colonies their color.
Describe the conidia color and spatial arrangement for A. fumigatus.
blue-green conidia

uniserate phialides

parallel conidia in chains

cover upper 2/3 of vesicle
Describe conidia color and spatial arrangement of A. flavus.
yellow-brown conidia

uniserate and biserate phialides

spiny conidiophore

cover entire vesicle - point in all directions
Describe conidia color and spatial arrangement of A. niger.
black colony

biserate phialides

cover entire vesicle and have radial pattern
A. niger rarely causes human disease; but if it does where is it most likely found?
otitis externa
How is aspergillus infection acquried?
inhalation of conidia
What are some diseases caused by aspergillus?
Allergic bronchopulmonary aspergillosis (no tissue invasion, hypersensitivity)
Aspergilloma (pre-exisitng cavities)
Invasive pulmonary aspergillosis (invade parenchyma)
Disseminated (non-contiguous infection)
Mycotoxicoses (aflatoxins)
What are predisposing factors to disseminated and/or invasive aspergillosis?
Neutropenia
Neoplasm
Organ transplantation
Chemotherapy - esp steroids
What is presumptive diagnosis of aspergillus infection if found in direct examination of tissue?
Septate hyphae with 45 angle branching
What is seen in cultures of aspergillus?
Hyaline mold grows in 1-2 days on routine fungal media @ 25.

Conidial pigmentation determines color
Which diseases are antibody tests available for?
Allergic disease and aspergilloma

(not good in invasive disease because patients are often unable to produce any antibodies)
What is the galactomannan test?
An antigen test for apsergillus that is often useful
What is therapy for allergic disease and aspergilloma?
allergic = steroids

aspergilloa = none, surgery if enlarges (must monitor)
What is therapy for invasive aspergillosis?
Voriconazole preferred

Also liposomal AmpB, Caspofungin
Describe the opportunists that are member of the order: Mucorales.
"Zygomycetes"

Ubiquitous in nature

Often found as common bread mold
What spp are included in Zygomycetes?
Rhizopus
Mucor
Absidia
What distinguished between the genera of zygomycetes?
Presence of rhizoids and their spatial arrangement in relation to sporangia.
What do zygomycetes look like in culture?
White, cottony, mould

Rapid growth @ 25 on std media

Turns dark upon sporulation
Describe the hyphae of zygomycetes?
NON-septate
Hyaline
Asexual reproduction = sporangia and sporangiospores
How do the rhizoids differentiate the different zygomycetes?
Rhizopus = rhizoids directly opposite sporangia

Absidia = rhizoids are between 2 sporangia

Mucor = NO rhizoids
How do you describe zygomycosis?
Acute and fulminant disease
What is the portal of entry for zygomycetes?
Respiratory

occasionally ear.
What is the most common clinical presentation in zygomycosis?
Rhinocerebral infection
--> rapidly progressive infection of sinues, orbits, and brain; with infarction and necrosis
--> associated with ketoacidotic diabetes
What are some other clinical presentations of zygomycosis?
Thoracic infections
Abdominal, gastric infection
Skin infection in burn patients
What is seen upon direct examination of Aspergillus spp.?
broad, NON-septate hyphae with 90 angle branching
What is therapy for zygomycosis?
Fulminant disease = liposomal AmpB
-- some efficacy but mortality is still high.

Surgical resection.
What is Pneumocystis jiroveci?
Pulmonary infection associated with clinical conditions of debilitation - secondary to immunosuppression and more recently with AIDS
What are some forms of P. jiroveci?
Trophic form
Uninucleate sporocyst
Mature spore case with 8 oval fusiform spores

*once thought to be a parasite
How is PCP acquried?
Respiratory tract is portal of entry
What is important for defense against PCP?
Alveolar macrophage and CD4+ T cells
What is the hallmark of PCP infection?
Interstitial pneumonitis and plasma cell infiltrate

Occasional extrapulmonary infection described.
Where must diagnosis of PCP be made from?
From lung tissue and bronchial washings and sputum

**Can't culture.
What is the morphological appearance of PCP
Has a collapsed football appearance
What is therapy for PCP?
1. Trimethoprim/sulfamethoxazole
**does not respond to antifungals
2. Also try clindamycin, etc.
3. Corticosteroids used concomitantly in acutely ill patients
Describe hyalohyphomycoses?
Opportunistic, rapidly growing, hyaline, monomorphic moulds

Often overlooked as contaminants

Usually infect skin and soft tissue but can cause disseminated disease
What are some common agents of hyalohyphomycoses?
Penicillium
Fusarium
Paecilomyces
Scopulariopsis
Acremonium