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159 Cards in this Set
- Front
- Back
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Why are very few fungi pathogenic to humans?
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most are considered opportunistic, they infect hosts with impaired immune systems
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Are fungi prokaryotes or eukaryotes? Why?
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Eukaryotes because they have a nuclear membrane and organelles
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What is their cell wall composed of?
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chitin, glucan, and mannan (unlike mammals)
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What is their cell membrane composed of?
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ergosterol --> fungal equivalent of cholesterol
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Define Yeast
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single-celled fungus that reproduces by BUDDING
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What are hyphae?
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microscopic, multicellular thread-like extensions of the cell
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What is the classification of hyphae?
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SEPTATE- porous cross walls between cells that allow free flow of protoplasm
ASEPTATE |
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Define pseudohyphae
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bud-like constrictions lacking free flow of protoplasm
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What are mycelia?
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MOULD- multicellular mat of hyphae
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Define thermal dimorphism
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The ability of a fungus to grow as a mould at room temperature (25 degrees C) and as a yeast at body temperature (37 degrees C)
This is done by GENE SWITCHING |
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List the dimorphic fungi
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histoplasma, blastomyces, coccidioides, paracoccidioides, sporothrix
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Do fungi reproduce sexually or asexually?
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both!
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What is the term for asexually derived fungal spores?
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conidia
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What is the term for the formation of asexual fungal spores?
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conidiogenesis
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How is a blastoconidium produced?
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budding of a daughter cell from an existing mother cell
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How does THALLIC REPRODUCTION occur?
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fission - fungal cells split in half
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What is the term for the asexual state of a fungus?
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anamorph
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What is the term for solely asexual fungi?
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fungi imperfecti
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Define heterothallic reproduction
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sexual reproduction between two separate mycelia (moulds)
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What is homothallic reproduction?
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sexual reproduction within a single mycelia
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What is the term for the sexual state of a fungi?
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teleomorph
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What do you call a fungi that can reproduce sexually?
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Fungi Perfecti
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What fungi can be gram stained? Why?
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Candida - has large, Gram + cells
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What fungi is india ink specific for? What does it stain?
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specific from Cryptococcus - stains its capsule
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Describe the CALCOFLOUR WHITE stain
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stain binds cell wall polysaccharides and flouresces white under UV light
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What fungi is the H&E stain specific for?
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Histoplasma
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What does the PAS stain do to fungi?
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stains cells pink
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What does the GMS stain do to fungi?
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stains the cell wall black
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What fungi has non-encapsulated extracellular yeast forms with pseudohyphae?
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Candida - if you see pseudohyphae then you know it's candida
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Which fungi has large round yeast cells surrounded by a thick capsule?
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Cryptococcus
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What are the key characteristics of Histoplasma?
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small
round intracellular & extracellular forms often found within macrophages |
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What are the key features of Blastomyces?
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large
round broad-based single bud from mother cell |
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What fungi has giant spherule containing endospores?
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Coccidioides
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This fungi looks like a pilot wheel on a ship or mickey mouse ears
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Paracoccidioides - multiple buds around mother cell
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These are small, cigar-shaped yeast cells
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Sporothrix
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What are the key features of Penicillium?
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Small
Oval-shaped cells with transverse septum divides by fission |
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What is the problem with culturing fungi?
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slow growing, require days to weeks of incubation, and they are often overgrown by faster growing bacteria in the media
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What are two general features when performing fungal cultures?
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1. usually held for 4 weeks to allow for slower growth
2. paired cultures at 25 & 37 degrees to identify thermal dimorphism |
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What is the most common fungal-specific culture? What are it's features?
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Sabaroud's agar - contains glucose & peptones, pH of 5.6 inhibits most bacteria
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What are the fungal specific cultures?
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1. Sabaroud's agar
2. Cornmeal agar 3. Potato-glucose agar |
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Describe the Fungal Isolator System:
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a fungal blood culture
1. venous blood is lysed and centrifuged 2. the sediment is plated on fungal specific media and incubated for 4 weeks |
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What test is used for presumptive identification of candida albicans?
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Germ Tube Test
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Describe the Germ Tube Test:
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1. yeast colonies are mixed with serum and incubated at 37 degrees for 3 hours
2. if it's candida albicans then microscopic exam reveals tube-like structures which are germinating hyphae |
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What can cause a false + Germ Tube Test?
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candida tropicalis
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Describe carbohydrate assimilation:
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Form of biochemical identification
Measures the ability to use a particular carbohydrate as the sole source of carbon |
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Which antigens can be detected in the urine?
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histoplasma or blastomyces
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What antigen can be detected in the serum or CSF?
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Cryptococcal
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What antigen is detected in the serum only?
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Aspergillus galactamannan
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Detection of Beta-glucan in the serum is indicative of what?
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Candida or Aspergillus
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List the 4 types of fungal infections in man:
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1. superficial
2. subcutaneous 3. mucosal 4. systemic |
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What is another name for superficial infections?
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Tinea
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What causes superficial infection?
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dermatophytes and possibly Candida
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What are the common symptoms of tinea?
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most symptoms result from the host's inflammatory response to the fungus
1. scaling of the skin 2. erythema 3. pruritis |
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What are the three genera of dermatophytes?
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1. Microsporum - infects the hair and skin
2. Trichophyton - infects the hair, skin, and nails 3. Epidermophyton - infects skin and nails |
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Superficial infection of the scalp
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tinea capitis
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Superficial infection of the body
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tinea corporis
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Superficial infection of the groin
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tinea cruris (jock itch)
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Superficial infection of the nail/nailbed
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tinea unguium/onychomycosis
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Superficial infection of the foot
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tinea pedis (athlete's foot)
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Superficial infection of the beard
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tinea barbae
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Superficial infection of the hand
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tinea manuum
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Animal to human transmission
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zoophilic
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soil to human transmission
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geophilic
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human to human transmission
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anthropophilic
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Define ectothrix
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superficial infection outside the hair shaft with cuticle destruction
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define endothrix
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superficial infection inside the hair shaft; cuticle remains intact
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How do you usually diagnose a Microsporum infection?
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Wood's lamp - microsporum glow blue-green
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What kind of infection does microsporum usually cause?
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an ectothrix infection
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How do you treat a superficial fungal infection?
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topical antifungal
- clotrimazole - nystatin oral therapy - azole - terbinafine |
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What is chronic infection the hair shaft called? What causes it?
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White piedra; Trichosporon
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What is the name of a superficial infection of the palms/soles? What causes it?
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Black piedra (tinea nigra); the yeast Hortaea
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What do you call a skin infection characterized by areas of hypopigmentation and possibly seborrheic dermatitis? What causes it?
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Tinea versicolor; Malassezia furfur
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What may cause bloodstream infection in patients receiving intravenous lipid preparations?
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Tinea versicolor
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What does Malassezia furfur look like on direct examination?
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spaghetti and meatballs
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What must you do to the media of Malassezia furfur?
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supplement the media with olive oil b/c it is a lipophilic yeast
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a fungal hand or foot infection where the nail and skin meet at the side or the base of a finger/toenail
What causes this? |
paronychia; a cutaneous candida infection
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What is the most common tinea unguium called? What causes it?
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onychomycosis; a cutaneous candida infection
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A cutaneous candida infection at the corners of the mouth
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angular cheilitis
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Candida infection of the penis
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balanitis
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another name for diaper rash
What causes it? |
perianal candidiasis; cutaneous candida infection
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What is a skin rash at the skin folds called (armpits/thighs etc)? What is a potential cause?
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Intertrigo; superficial candida infection
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How do subcutaneous fungal infections usually occur?
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traumatic implantation of a fungus, usually from the soil, into deeper layers of skin
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What are the typical symptoms of a Chromomycosis infection?
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chronic, warty, nodular lesions that are cauliflower-like
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What geographic region do chromomycosis usualy occur?
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tropics/subtropics (Madagascar, Brazil, Costa Rica)
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What are the direct findings of chromomycosis?
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unique cells called sclerotic bodies or "copper pennies"
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Culturing at 25 degrees C favors what type of fungi? 37 degrees?
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25 favors mycelia
37 favors yeast |
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What agents cause chromomycosis?
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dark-walled moulds
1. Fonsecaea (most common) 2. Phialophora 3. Cladosporium |
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How does chromomycosis usually enter the body?
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infection occurs following a puncture wound (walking barefoot)
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Treatment of chromomycosis
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itraconazole and local excision of "cauliflower-like" lesions
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What is another name for a mycetoma?
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madura foot
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What is the clinical presentation of mycetoma?
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localized, slow-growing deforming lesions involving the cutaneous and subcutaneous tissues of the foot/hand
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What is the bacterial form of mycetoma? Which bacteria? How do they differ? How does the bacterial form differ form the fungal form?
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actinomycotic mycetoma
1. Actinomyces - white/yellow sulfer granules 2. Nocardia - white/yellow granules 3. Streptomyces - yellow/brown granules Bacterial form is more locally invasive infecting underlying muscle and bone |
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What is the fungal form of mycetoma?
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Eumycotic mycetoma
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What is the most common cause of eumycotic mycetoma in the US?
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Pseudallescheria boydii
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What is the treatment for mycetomas?
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antimicrobial therapy plus surgical resection
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What does pseudallescheria boydii cause? What population does it usually occur in?
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1. mycetoma
2. pulmonary, sinus, bone, and CNS infections Usually infects the immunocompromised |
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What causes sporotrichosis?
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sporothrix schenckii
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What is the common name for sporotrichosis?
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Rose-handlers disease
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What is the clinical course of sporotrichosis?
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- prick by a thorn
- subcutaneous nodule gradually appears - this nodule becomes necrotic and ulcerates - the ulcer heals, but new nodules pop up nearby and along the lymphatic tracts up the arm |
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What is an important feature about sporothrix schenckii?
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it is dimorphic
-yeast at 37 -hyphae at 25 |
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What are the 2 types of sporotrichosis?
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1. Lymphocutaneous - ulceration at site of infection with spread via lymphatics
2. Disseminated disease with spread to the lungs (in immune compromised) |
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What are the diagnostic features of sporothrix schenckii?
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1. dimorphic
2. cigar-shaped yeast forms in tissue 3. culture - most reliable method of diagnosis |
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What is the treatment for sporotrichosis?
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itraconazole - mild - moderate disease
amphotericin B for severe/disseminated disease |
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Candida is normal flora of what?
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GI and female reproductive tracts
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When do chronic, recurrent candida infections occur?
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in immune compromised (HIV, diabetes)
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What are predisposing factors to candida infection?
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1. antibacterial or steroid use
2. Neutropenia 3. chemotherapy |
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What are the types of candida mucosal infections?
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1. oral candidiasis - thrush; creamy white plaques
2. vaginitis 3. esophagitis - associated with dysphagia, odynophagia 4. cystitis - bladder infection associated with foley catheter use, diabetes, broad-spectrum antibacterial therapy |
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What is the most common candida species?
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Candida albicans
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What are the three candida infections that can occur in normal hosts?
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1. oral thrush
2. vaginitis 3. diaper rash |
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What is the clinical presentation of oral thrush?
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patches of creamy white exudate with a reddish base that covers the mucous membranes of the mouth
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What is the treatment for oral thrush?
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1. swish and spit preparations of nystatin or amphotericin B
2. suck on imidazole candies |
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What are the symptoms of candida vaginitis?
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vaginal itching and discharge (thick copious secretions wetting the underwear)
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What does the speculum exam reveal in candida vaginitis?
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inflamed vaginal mucosa and patches of cottage cheese-appearing white clumps affixed to the vaginal wall
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What is the treatment for candida vaginitis?
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a single dose of oral fluconazole is very effective
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What is the clinical presentation of candida diaper rash?
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warm moist areas under diapers (between skin folds in adults) become red and macerated (separation of skin)
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What infections can occur in an immune compromised patient with candida albicans infection?
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1. same as healthy patients (oral thrush, vaginitis, diaper rash)
2. esophagitis 3. disseminated |
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What is the clinical presentation of candida esophagitis? Can this occur in healthy patients?
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extension of thrush into the esophagus causing burning substernal pain that is worse with swallowing;
candida does not infect the esophagus of a healthy person |
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What is meant by disseminated candida infection?
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candida infection can spread to the bloodstream and virtually every organ
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What must be checked if systemic candidiasis is suspected?
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the retina (endophthalmitis) - look for multiple white fluffy candidal patches
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Candida is part of the normal human flora. Where shouldn't it be found?
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candida isolation in the blood is never normal
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What is the treatment for candida infection?
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1. amphotericin B
2. fluconazole 3. echinocandin |
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This fungus' main manifestation is meningoencephalitis
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cryptococcus neoformans
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Where is cryptococcus neoformans found in nature?
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pigeon droppings (guano)
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cryptococcus neoformans infection occurs predominantly in what population?
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immune compromised (3/4 of cases);
10% of AIDS patients develop cryptococcosis |
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How does cryptococcus neoformans gain entry into the body? How does it spread? Where does it spread to?
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it is inhaled and causes local lung infection; the yeast spreads via the blood; and travels to the brain
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What is the prognosis of cryptococcus neoformans without treatment?
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cryptococcal meningitis is fatal without treatment, because cerebral edema progresses to eventual brainstem compression
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Other than meningitis, what can cryptococcus neoformans infection cause?
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pneumonia, skin ulcers, and bone lesions
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What is the key to diagnosis of cryptococcus neoformans?
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preforming a lumbar puncture and analyzing the CSF
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What is a defining characteristic of cryptococcus neoformans?
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it has a polysaccharide capsule
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What test is (+) 50% of the time for cryptococcus neoformans? What does this (+) test look like?
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India ink stain; shows yeast cells with a surrounding halo --> the halo is its polysaccharide capsule
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What is a more sensitive test for cryptococcus neoformans? What does it detect?
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cryptococcal antigen test; detects cryptococcal polysaccharide antigens
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What is the gold standard for cryptococcus neoformans diagnosis?
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culture (used to confirm previous tests: india ink & cryptococcal antigen test)
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How is cryptococcus neoformans infection treated?
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amphotericin B with flucytosine for first 2 weeks followed by fluconazole for at least 8 weeks
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What are three similar systemic fungal infections?
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1. Histoplasma capsulatum
2. Blastomyces dermatitidis 3. Coccidioides immitis (cryptococcus neoformans also causes systemic infection but is a little different) |
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What is an infectious characteristic of Histoplasma capsulatum, Blastomyces dermatitidis, & Coccidioides immitis?
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they are all dimorphic fungi
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How do Histoplasma capsulatum, Blastomyces dermatitidis, & Coccidioides immitis differ in nature vs in the human host?
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In the soil they grow as mycelia and release spores in the air
These spores are inhaled by humans and at 37 degrees they grow as yeast cells |
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What is the geography of Histoplasma and Blastomyces?
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they are endemic to the areas that drain into the Mississippi River
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What is the geography of Coccidioides?
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it's endemic to the Southwestern US (Arizona, New Mexico, southern California)
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H, B, and C have similar disease mechanisms to what other infection?
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mycobacterium tuberculosis
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How are HB&C acquired? How does this compare to TB?
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via inhalation of aerosolized spores (from soil or bird guano); TB is also inhaled via spores but the fungal infections are not transmitted from person to person
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What is the course of action of HB&C?
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inhalation, local infection in the lungs, bloodstream dissemination
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What are the 3 clinical presentations of HB&C?
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1. Asymptomatic
2. Pneumonia 3. Disseminated |
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Describe asymptomatic HB&C infection:
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the majority of cases of HB&C infection are mild respiratory illnesses that go unreported
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Describe the pneumonia associated with HB&C:
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a mild pneumonia can develop with fever, cough, and chest X-ray infiltrates
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What do a small percentage of people with HB&C infection progress to?
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chronic cavitary pneumonia --> weight loss, night sweats, and low-grade fever (this is much like chronic TB pneumonia)
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In what population does the disseminated form of HB&C infection occur?
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immune compromised
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What is the problem with doing a skin test for a HB&C infection?
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many people have been previously exposed to HB&C asymptomatically and will produce a positive test anyway
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How are HB&C infections diagnosed?
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they are best diagnosed by biopsy of the affected tissue (lung or skin biopsy)
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How are HB&C infections treated?
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- mild Histoplasmosis and Coccidioidomycosis usually go untreated
- Blastomyces and severe H&C infections require aggressive amphotericin B or intraconazole treatment |
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What fungi is obtained from the soil and endemic to Brazil?
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paracoccidioides brasiliensis
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What diseases in humans does aspergillus flavus cause?
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1. Allergic Broncho-Pulmonary Aspergillosis (ABPA) - allergic reaction in the lung airways
2. Aspergilloma - infection in preformed lung cavities 3. invasive aspergillosis - invasive infection of the lungs |
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Describe ABPA:
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Allergic Broncho-Pulmonary Aspergillosis:
1.person inhales spores and has a type 1 hypersensitivity reaction (IgE mediated) causing bronchospasm, inc IgE antibodies, and blood eosinophelia 2. also manifests a type 4 reaction (delayed type cell-mediated allergic reaction) characterized by inflammation and lung infiltrates |
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How is ABPA treated?
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corticosteroids
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Describe an aspergilloma:
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occurs in someone with lung cavitations from TB or malignancies; it is an aspergillus fungal ball in the cavity
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What is the treatment for aspergilloma?
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usually no treatment necessary
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Immune compromised patients get which form of aspergillus infection?
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invasive aspergillosis
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How does invasive aspergillosis present?
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slowly progressive (asymptomatic) pneumonia characterized by nodular infiltrates on the chest CT scan
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What is the prognosis of a patient infected with invasive aspergillosis? How is it treated?
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this is extremely lethal without treatment; treated with the most powerful antifungals: voriconazole or amphotericin B
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What is the toxin produced by aspergillus flavus? What does it cause?
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aflatoxin; causes liver damage and liver cancer
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