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72 Cards in this Set
- Front
- Back
Most fungal infections in hosptials are opportunistic. What is the causative agent of most of these infections?
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C. albicans
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Describe opportunistic fungi.
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Ubiquitous and low virulence
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Mycotic infection is more/less often due to opportunistic fungi in areas with endemic pathogenic dimorphs.
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More often opportunistic fungi even in pathogenic endemic areas.
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Name some Candida species that are significant human pathogens.
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C. albicans
C. glabrata C. tropicalis C. parapsilosis C. kruseii |
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How does C. albicans reproduce?
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It is an oval yeast that reproduces by budding = blastoconidia
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What are pseudohyphae?
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Buds that fail to detach the mother cell and instead elongate to form pseudohyphae.
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What do colonies of C. albicans look like on Sabouraud dextrose agar?
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White and creamy after 24-48 hours @ 35.
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What is CHROMagar candida?
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A selective and differential medium for presumptive identification of Candida species.
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What is used in the laboratory to ID C. albicans?
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1. Germ tube test - only C. albicans
2. Chlamydoconidia formation - only C. albicans 3. Carb assimilations and fermentations |
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What is the germ tube test?
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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. |
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Describe chlamydioconidia formation.
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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" |
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Why is Candida infection usually of endogenous origin?
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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. |
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What are two ways Candida infection may occur?
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1. Host abnormalities that allow Candida to invade normally sterile tissue
2. Overgrowth in sites where Candida normally exists in controlled sites |
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What are some common sites of infection with Candida?
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Urogenital tract
Oropharynx Skin CV system |
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What are some situations where cutaneous infection with Candida may occur?
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1. burns
2. chronic moisture or maceration ** due to breakdown of skin integrity and loss of barrier protection |
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What is chronic mucocutaneous candidiasis?
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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 |
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What are some predisposing factors for Candida infection?
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- 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 |
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What are some virulence factors of C. albicans?
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1. Grows at high temperatures
2. Adheres to cell surfaces 3. Produces proteases |
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What is difficult about diagnosing Candida infection?
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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 |
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Is serology useful for candida diagnosis?
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Serology is also of limited use because Candida is endogenous.
Ab and Ag tests have not been effective. |
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What is therapy for Candida infections?
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Topicals = nystatin, miconazole, clotrimazole
Invasive/disseminated = AmpB, liposomal AmpB, fluconazole, voriconazole |
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Why are infections due to other species of Candida increasing?
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Appears to be rising due to resistance of some of them to fluconazole
C. glabrata, C. kruseii |
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What kinds of Candida infections are found in IV drug users?
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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. |
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What is the major reservoir for C. neoformans?
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Pigeons.
Up to 50 million organisms can be found per gram of feces No disease in pigeons |
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What is the morphology of C. neoformans?
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A yeast that reproduces by single or double buds
**No germ tube or pseudohyphae formation! |
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What does C. neoformans produce that serves as a virulence factor and is the basis for its serotyping?
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Polysaccharide capsule
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How is C. neoformans acquired by the human?
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Inhalation but primary infection here is usually subclinical
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Who has the most life-threatening Cryptococcus infection?
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Seen in patients with impaired CMI especially T cells.
Seen in lymphoma and AIDS #1 cause of fatal fungal infection in AIDS patients |
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What tissue does C. neoformans have a predilection for?
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CNS
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How are samples prepared for direct examination of cryptococcus?
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1. India ink prep of CSF - LOW sensitivity
2. Histopathological stains of tissue - GMS, PAS, mucicarmine stain (stains capsule) |
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Can C. neoformans be cultured?
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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 |
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What are four ways to ID C. neoformans?
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1. Demonstrate capsule by india ink
2. Production of blastospores only. 3. Urease production - urea agar 4. Pigmented colonies on caffeic acid agar |
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What is used for serological diagnosis of cryptococcus?
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Latex agglutination test to detect cryptococcus polysaccharide in CSF and serum
**more sensitive than India ink |
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What is therapy for cryptococcus infection?
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AmpB +/- 5FC (synergists)
Follow with fluconazole for long term suppression of cryptococcus in AIDS |
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What are some species of Aspergillus that cause human disease?
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A. fumigatus
A. flavus A. niger A. terreus (resistant to AmpB!) |
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What is the morphology of Aspergillus spp.?
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Rapidly growing
monomorphic MOULDS ubiquitious in most environments |
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Describe the mycelium of Aspergillus spp.
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Septate, hyaline hyphae
Conidiophores have terminal vesicle with phialides that produce chains of conidia Conidia give colonies their color. |
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Describe the conidia color and spatial arrangement for A. fumigatus.
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blue-green conidia
uniserate phialides parallel conidia in chains cover upper 2/3 of vesicle |
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Describe conidia color and spatial arrangement of A. flavus.
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yellow-brown conidia
uniserate and biserate phialides spiny conidiophore cover entire vesicle - point in all directions |
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Describe conidia color and spatial arrangement of A. niger.
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black colony
biserate phialides cover entire vesicle and have radial pattern |
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A. niger rarely causes human disease; but if it does where is it most likely found?
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otitis externa
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How is aspergillus infection acquried?
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inhalation of conidia
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What are some diseases caused by aspergillus?
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Allergic bronchopulmonary aspergillosis (no tissue invasion, hypersensitivity)
Aspergilloma (pre-exisitng cavities) Invasive pulmonary aspergillosis (invade parenchyma) Disseminated (non-contiguous infection) Mycotoxicoses (aflatoxins) |
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What are predisposing factors to disseminated and/or invasive aspergillosis?
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Neutropenia
Neoplasm Organ transplantation Chemotherapy - esp steroids |
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What is presumptive diagnosis of aspergillus infection if found in direct examination of tissue?
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Septate hyphae with 45 angle branching
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What is seen in cultures of aspergillus?
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Hyaline mold grows in 1-2 days on routine fungal media @ 25.
Conidial pigmentation determines color |
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Which diseases are antibody tests available for?
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Allergic disease and aspergilloma
(not good in invasive disease because patients are often unable to produce any antibodies) |
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What is the galactomannan test?
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An antigen test for apsergillus that is often useful
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What is therapy for allergic disease and aspergilloma?
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allergic = steroids
aspergilloa = none, surgery if enlarges (must monitor) |
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What is therapy for invasive aspergillosis?
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Voriconazole preferred
Also liposomal AmpB, Caspofungin |
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Describe the opportunists that are member of the order: Mucorales.
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"Zygomycetes"
Ubiquitous in nature Often found as common bread mold |
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What spp are included in Zygomycetes?
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Rhizopus
Mucor Absidia |
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What distinguished between the genera of zygomycetes?
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Presence of rhizoids and their spatial arrangement in relation to sporangia.
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What do zygomycetes look like in culture?
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White, cottony, mould
Rapid growth @ 25 on std media Turns dark upon sporulation |
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Describe the hyphae of zygomycetes?
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NON-septate
Hyaline Asexual reproduction = sporangia and sporangiospores |
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How do the rhizoids differentiate the different zygomycetes?
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Rhizopus = rhizoids directly opposite sporangia
Absidia = rhizoids are between 2 sporangia Mucor = NO rhizoids |
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How do you describe zygomycosis?
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Acute and fulminant disease
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What is the portal of entry for zygomycetes?
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Respiratory
occasionally ear. |
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What is the most common clinical presentation in zygomycosis?
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Rhinocerebral infection
--> rapidly progressive infection of sinues, orbits, and brain; with infarction and necrosis --> associated with ketoacidotic diabetes |
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What are some other clinical presentations of zygomycosis?
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Thoracic infections
Abdominal, gastric infection Skin infection in burn patients |
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What is seen upon direct examination of Aspergillus spp.?
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broad, NON-septate hyphae with 90 angle branching
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What is therapy for zygomycosis?
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Fulminant disease = liposomal AmpB
-- some efficacy but mortality is still high. Surgical resection. |
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What is Pneumocystis jiroveci?
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Pulmonary infection associated with clinical conditions of debilitation - secondary to immunosuppression and more recently with AIDS
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What are some forms of P. jiroveci?
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Trophic form
Uninucleate sporocyst Mature spore case with 8 oval fusiform spores *once thought to be a parasite |
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How is PCP acquried?
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Respiratory tract is portal of entry
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What is important for defense against PCP?
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Alveolar macrophage and CD4+ T cells
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What is the hallmark of PCP infection?
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Interstitial pneumonitis and plasma cell infiltrate
Occasional extrapulmonary infection described. |
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Where must diagnosis of PCP be made from?
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From lung tissue and bronchial washings and sputum
**Can't culture. |
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What is the morphological appearance of PCP
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Has a collapsed football appearance
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What is therapy for PCP?
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1. Trimethoprim/sulfamethoxazole
**does not respond to antifungals 2. Also try clindamycin, etc. 3. Corticosteroids used concomitantly in acutely ill patients |
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Describe hyalohyphomycoses?
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Opportunistic, rapidly growing, hyaline, monomorphic moulds
Often overlooked as contaminants Usually infect skin and soft tissue but can cause disseminated disease |
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What are some common agents of hyalohyphomycoses?
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Penicillium
Fusarium Paecilomyces Scopulariopsis Acremonium |