Fungi Lecture Exam Flashcards
What does it mean if a fungi is dimorphic?
Has two forms yeast(37C) and mold (25C)
What are some examples of dimorphic fungi?
Blastomyces dermatitidis.
Histoplasma capsulatum.
Coccidioides immitis.
Paracoccidioides brasiliensis.
Sporothrix schenckii
Define Teleomorph
Can produce ascospores (sexual spores)
Define anamorph
Produce conidia asexual spores
Define Synapomorphs
More than one asexual form of fungi
Describe yeast
Grows at 37C, unicellular, reproduce via budding (process outpouching)
What are germ tubes?
Incomplete cell division that starts with outpouching of cell wall that becomes tubular with no construction point. Its an initial stage of true hyphae formation.
What is a distinguishing feature of candida albicans from other yeasts?
Forms germ tubes
Describe hyphae in molds
Long filamentous structure in other words long branching tubes (not germ tube).
Describe mycelium
Mass network of hyphae
Describe Vegatative hyphae
Anchors old and absorbs nutrients. Tiny filiments
Reproductive hyphae describe it you must.
Hyphae with reproductive structures (conidia, sporangium, and etc).
What is vegetative mycelium
Network or mass of vegetative hyphae
True or false, Coccidioides is thermally dimorphic in other words are the two forms of coccidioides dependent on temperature?
No they do not dependent on temperature per micro book page 758.
Most fungi share what characteristics?
- Chitin in the cell wall
- Ergosterol in the cell membrane
- Reproduction by means of spores, produced asexually or
sexually - Lack of chlorophyll
- Lack of susceptibility to antibacterial antibiotics
- Saprophytic nature (derive nutrition from organic materials)
Clinicians divide clinically significant fungi into what categories?
- Superficial (cutaneous) mycoses
- Subcutaneous mycoses
- Systemic mycoses
- Opportunistic mycoses
What is the working schema for a fungi specimen?
Gjgfj
What is hyaline?
A hyphae with no pigments
List some virulence factors of fungi (general)
- The organism’s size (with inhalation, the organism must
be small enough to reach the alveoli) - The organism’s ability to grow at 37°C at a neutral pH
- Conversion of the dimorphic fungi from the mycelial
form into the corresponding yeast or spherule form in
the host - Toxin production
Aerial mycelium is…?
Mycelium that grows upward or outward from the agar. Described as cottony growth texture.
What is septate in a fungi?
Divisions between cells. The cells have pores that allow cytoplasm and nutrients. An example of a septate fungi is aspergillus.
What is sparsely septate?
Its considered non-septate or aseptate. They are hyphae cells with no division. Examples of fungi that are aseptate is zygomycetes and mucor.
What is dematiaceous?
Pigmented or melanized hyphae
What are superficial cutaneous mycoses?
- Can infect hair, skin, nails or all three depending on genus
*They prefer the keratinized layer of the body and do not infect deeper in the body.
What organism causes black piedra?
Piedraia hortae causing black spots on hair shaft
What organism causes white piedra?
Trichosporon beigelii causing white spots on the hair shaft
What causes Pityriasis versicolor?
Malassezia furfur
What are examples of subcutaneous mycoses?
Chromoblastomycosis
Sporotrichosis
Mycetoma
Phaeohyphomycosis
What are examples of systemic mycoses?
Aspergillosis
Blastomycosis
Candidosis
Coccidioidomycosis
Histoplasmosis
Cryptococcus
Trichosporonosis
What are examples of opportunistic mycoses?
Aspergillosis
Candidosis
Cryptococcosis
Mucormycosis
Geotrichosis
Trichosporonosis
Between piedraia hortae and trichosporon beigelli, which one can produce asci?
Piedraia hortae (causes black piedra)
Tinea barbae is where on the body?
The beard
Tinea manuum is where on the body?
The hands
Tinea capitis is where on the body?
scalp or head
Tinea pedis is where on the body?
The feet or foot example is athletes foot
Tinea corporis is where on the body?
lesions that may involve the trunk, neck, arms, and legs
What kind of tinea can micorsporon canis cause?
Tinea corporis
Tinea capitis
Tinea barbae
Tinea manuum
Epidermophyton floccosum can cause what tinea?
Tinea cruris
Tinea pedis
Tinea corporis
Onychomycosis (infect nails)
Describe chromoblastomycosis.
*Chronic fungal infection of skin & subcutaneous tissue
* Traumatic inoculation of specific group of dematiaceous fungi
* Non-healing ulcers
*Brown pigmented wart like lesions
*Verrucous cauliflower-like dermatitis
*Common in troupical and subtropical countries
*Secondary bacterial infection common
What are organisms that could cause chromoblastomycosis?
Fonsecaea pedrosoi
Phialophora verrucosa
Cladophialophora carrionii
Rhinocladiella aquaspersa
Organism that causes Rose gardener’s disease?
Sporothrix schenckii
How does sporothrix schenckii spread?
Infects an opening of the skin (damaged skin by thorns) and usually stays subcutaneous. In rare cases the organism will spread through lymphatic channels to visceral organs.
What are organisms that may cause eumycotic mycetoma?
Pseudallescheria boydii - Cleistothecium release ascospores (looks like pacman)
Acremonium falciforme
Madurella mycetomatis
Curvularia spp
Exophiala jeanselmei
What is a mycetoma?
Appears as firm, painless masses under the skin. These masses usually appear on a person’s foot but can form anywhere on the body. The mycetoma masses start small, but over time they can grow larger, develop oozing sores, and cause the affected limb to become deformed or unusable.
Class description
Can be anywhere on the body, but the foot most common
Draining sinus tracts that communicate with the exterior of the body
Granules composed of aggregates of the organism
What organism(s) causes candidiasis?
Candida spp. or most common occurring, candida albicans. Its an opportunistic fungi and a normal flora of the human body.
What can worsen a fungus infection?
The use of antibiotics or/and chemotherapy.
What is chronic paronychia?
An inflammatory recalcitrant disorder affecting the nail folds. It can be defined as an inflammation lasting for more than 6 weeks and involving one or more of the three nail folds. Usually caused by mechanical or chemical factors sometimes infectious etiology like gunal infection especially Candida species. Increased risks are depends on occupation for example dishwasher, bartender, and housekeeper. Another increased risk is with medications such as antibiotics and immunosuppresors (diabetes, HIV, and malignancy).
What are the two most common genus to cause candidal onychomycosis?
Onychomycosis is caused by various organisms, most often dermatophytes of the genus Trichophyton. Other organisms include Candida, which is more common in fingernail infections (eFigure A) and in patients with chronic mucocutaneous candidiasis
What is perleche?
Perleche, also known as angular cheilitis, is a disease characterized by sores or “crusts” at the labial commissure or corners of the mouth
List common candida infections
Thrush
Vulvovaginitis
Pulmonary infections
Eye infections
Endocarditis
Meningitis
Fungemia
On chromagar for fungus, a colony of yeast is growing with a mauve to dark mauve color. What could this fungi be?
Candida glabrata
On chromagar for fungus, a colony of yeast is growing with a Light rose to pink with whiteish border. What could this fungi be?
Candida krusei
What fungi can be found in pigeon droppings?
Cryptococcus neoformans
Describe a cryptococcus infection
Headache, fever, neck stiffness, abnormal gait, cranial nerve palsies less common, papilledema, confusion, convulsions, and coma.
*May present as pulmonary infection but worse as the infection goes on.
Cryptococcus lab tests?
*India ink to observe the capsule trait
*Gram stain to examine shape of yeast
*Urease test positive
*Bird see agar to observe brown pigmentation from the phenol oxidase metabolizing caffeic acid. This characteristic is observed in C. neoformans and C. gattii
*Serological test that targets the capsular polysaccharide antigens
Malassezia furfur in children and adults?
Causes tinea versicolor and disseminated infection in infants and young children and adults receiving lipid replacement therapy. Its also associated with gunemia in immunocompromised patients especially neonates in intensive care settings.
Describe Malassezia culture needs
Most common method is to overlay Saouraud’s dextrose agar containing cycloheximide with olive oil or alternatively to use a more specialized media like Dixon’s agar which contains glycerol mono-oleate
Malassezia microscopic characteristics
“Spaghetti and meatballs” - pseudohyphae and spores
“Milk Bottles” - yeast
Examples of subcutaneous phaeohyphomycosis caused by darkly pigmented fungi
Exophiala
Wangiella
Fonsecaea
Alternaria
Examples of systemic fungi
–Histoplasma
–Blastomyces
–Coccidioides
–Paracoccidioides brasiliensis
–Sporothrix
–Aspergillis
List some info about Histoplasma capsulatum.
Worldwide
Inhalation of spores
Exposure to bird including chickens and bats (feces)
Phagocytized by macrophages
Calcification in lungs, liver, and spleen
Can cause acute pulmonary disease
Can reactivate
Can disseminate: fatal
Lab tests for histoplasma capsulatum?
- Culture is the gold standard, but takes weeks
*Antigen tests are fairly accurate – Sputum, urine, and blood
*May see yeast within macrophages or lesions
*Yeasts may be acid-fast
List some info about Blastomyces.
*Blastomycosis
*Aka Gilchrist’s Disease, Chicago Disease
*North america and Africa
*Occupational exposure – outdoors
*Pulmonary disease
*Multi-organ in immunocompromised
*Skin is involved in 40-80% of the cases and multiple organs are infected in *about half of the cases
*ACID FAST YEAST
Lab tests for Blastomyces?
*Culture is the gold standard but takes weeks
*Serology not useful due to cross creativity and antigen detection is not sensitive (false positives)
*Presumptive ID depends on visualization of broad-based yeast.
*PCR, you can PCR anything as long as its been sequence. Just target a unique piece of DNA in the species.
Describe Coccidioides immitis
*Alternating barrel characteristic under the microscope
*Coccidioidomycosis or Valley Fever
*Southwestern US – contaminated soil
*MOST VIRULENT (arthroconidia)
*Usually resolves (6 weeks)
*Immunity
*Detected with coccidioidin skin test
*Can disseminate
*Characterized by a saprobic mycelial phase that gives rise to infectious arthroconidia which in host tissue, convert into a morphologically distinct spherule-endospore phase.
*The multiphasic cycle presents a formidable challenge to the host
Describe Paracoccidioides brasiliensis
*South American blastomycosis (paracoccidioidomycosis)
*Chronic, progressive
*Some strains have proteases
*Endemic in central and south america
*Nasal, oropharyngeal lesions, pulmonary dissemination
*Mariner’s wheel in yeast form (microscope)
What aspergillus produces aflatoxin?
Aspergillus flavus
Fungi identification?
*Molds are identified regardless of the source
*Molds that fail to sporulate may be reported but *not identified if dimorphism has been ruled out
*Usually identified based on macroscopic and *microscopic morphology
*YEAST @ 37 C Filamentous mold - RT 25 C
Fungi Safety?
*ALL MOLDS SHOULD BE HANDLED IN CLASS II BSL
*Plates should be sealed
*Yeasts can be handled on benchtop (within safety hood)
What are two genus that can be presumptive ID?
C. albicans - germ tube
Cryptococcus - Capsule trait (using india ink) & antigenic testing with a serology test.
Mold Identification are based on…?
*Growth rate
*Colonial morphology
*Microscopic technology
Microscopic observation of fungi involves…
*Tape preparation
*Wet mount (tease prep_
*Microslide culture
*Lactophenol cotton (or aniline) blue
What are common medias used?
*Sabouraud Dextrose Agar – will grow most yeast and molds
*Cornmeal agar – chlamydospores in Candida
*Chromagar – Candida
*Niger seed - Cryptococcus
*Oil overlay for – Malassezia
*Mycosel – filamentous fungi
Differential agar used can be…?
*Chromagar for fungi and Cottonseed conversion. *Cottonseed Agar provides conversion of dimorphic Blastomyces from mold to yeast.
*Trichophyton agars 1-7
*Urease test
What is the purpose of corn meal agar?
Its a general purpose agar. For studying mycelium or pseudomycelium formation, and for the study of Candida species for the chlamydospore production
What are some other general purpose agars for fungi besides cornmeal agar?
SABS or potatoe based such as PFA, PDA
What is a selective agar for fungi?
Mycosel contains cycloheximide that inhibit cryptococcus and aspergillus
What is an agar specifically for histoplasma?
BHI
Polyenes such as amphotericin B does what?
Binds to ergosterol leading to increase cell permeability leading to cell death
Azoles such as fluconazole, itraconazole, voriconazole, posaconazole targets?
Impairs ergosterol synthesis
Nucleoside analogs such as flucytosine does what?
Disrupts pyrimidine metabolism (in the cell’s nucleus)
Echinocandin such as caspofungin and micafungin does…?
Inhibits formation of 1,3 glucan
Allylamine such as terbinafine does…?
Disrupts fungal cell membrane (squalene oxidase)
Susceptibility tests are done when?
When therapeutic fails or when there is a sterile site infection.
How can Trichphyton mentagrophyte be differentiated from trichophyton rubrum?
T. mentagrophytes are urease positive. T. rubrum is urease negative.
Calcofluor white is…
The staining procedure using Calcofluor White Stain is a rapid method for the detection of many yeasts and pathogenic fungi such as Microsporidia, Acanthamoeba, Pneumocystis, Naegleria, and Balamuthia species.
KOH is…
The skin lesion KOH exam is a test to diagnose a fungal infection of the skin.
Nucleic acid test is available for…
Histoplasma, Blastomycese, Coccidioides
In the exo antigen test a band, cross, and partial cross means what?
Band - Identity
Cross - No identity
partial - partial identity
India ink… is?
India ink staining of cerebrospinal fluid is a sensitive test for the presence of Cryptococcus neoformans. Cryptococcus is surrounded by a thick capsule; the carbon grains cannot penetrate the capsule resulting in a clear halo around the refractile wall of the yeast
List some examples of genus or species that are infectious in yeast form.
Candida albicans
Cryptococcus neoformans and C. gattii
Trichosporon
Malassezia furfur
