II. DIAGNOSTIC MYCOLOGY Flashcards
produce moist, creamy, opaque or pasty colonies on media
Yeast
produce fluffy, cottony, woolly, or powdery colonies
Filamentous fungi or Molds
fungal pathogens that exhibit either a yeast or yeastlike phase and filamentous forms
Dimorphic
when dimorphism is temperature-dependent
Thermally dimorphic
mold form at
25°C to 30°C
yeast form t
35°C to 37°C
fungi that have more than one independent form or spore stage in their life cycle
Polymorphic fungi
Fungi have been categorized into three well-established phyla:
Zygomycota
Ascomycota
Basidiomycota
This diverse group of fungi includes organisms that produce sparsely septate hyphae and exhibit asexual reproduction by sporangiospores and sexual reproduction by the production of zygospores.
Zygomycota
fungi that reproduce asexually by the formation of conidia (asexual spores) and sexually by the production of ascospores.
Ascmycota
fungi that reproduce sexually through the formation of basidiospores on a specialized structure called the basidio
Basidiomycota
fungal infections that involve hair, skin, or nails without direct invasion of deeper tissue
Superficial (cutaneous) mycoses
infections that are confined to the subcutaneous tissue without dissemination to distant sites
Subcutaneous mycoses
Four categories of mycoses according to the type of infection:
Superficial (cutaneous) mycoses
Subcutaneous mycoses
Systemic mycoses
Opportunistic mycoses
infect immunocompromised hosts. ______________ include almost any fungus present in the environment
Opportunistic pathogens
Virulence factors
Size
Temp and ph (37°C at a neutral pH)
Conversion of the dimorphic
Toxin production
most common specimens collected for fungal culture
Respiratory tract secretions
prevents overgrowth by rapidly growing molds and should be included in at least one of the culture media
antifungal agent cycloheximide
are satisfactory for the recovery of fungi
Agar plates or screw-capped agar tubes
___________ are preferred, because they provide better aeration of cultures, a large surface area for better isolation of colonies, and greater ease of handling
Plates
Dishes should be opened and examined in a __________________
CERTIFIED BIOLOGICAL SAFETY CABINET
After inoculation, tubes should be placed in a _______________ for at ______________ to allow the specimen to absorb to the agar surface and prevent settling at the bottom of the tube.
Horizontal position
1 to 2 hours
___________ are unsatisfactory for fungal cultures.
Cotton-plugged tubes
● Cultures should be incubated at room temperature, or preferably at _______________ before they are reported as ___________
● Cultures should be examined at __________weekly during incubation.
30°C, for 21 to 30 days
Negative
Atleast three times
Addition of ___________________ and _________________ to media has been advocated to inhibit the growth of contaminating molds and bacteria, respectively. However, better results have been achieved using a combination of ________________________________ as antibacterial agents. _______________ at a concentration of 5 mg/mL may be used.
0.5 mg/mL of cycloheximide
16 mg/mL of chloramphenicol
5 mg/mL of gentamicin and 16 mg/mL of chloramphenicol
Ciprofloxacin
This important procedure often can provide the first microbiologic proof of the cause of disease in patients with fungal infection and guide the selection of appropriate media to support growth.
Direct Microscopic Examination
Detection of mycobacteria, Nocardia spp. And some isolates of Blastomyces spp
Acid-fast stain and partial acid-fast stain
Detection of mycobacteria and Nocardia spp.,
Auramine-rhodamine stain
Excellent screening tool; sensitive and affordable.
Auramine-rhodamine stain
detects fungi rapidly because of bright fluorescence.
Calcofluor white stain
Commonly performed on most clinical specimens submitted for bacteriology; detects most fungi.
Gram stain
Detection of Cryptococcus spp. in CSF
India ink
Diagnostic of meningitis when positive in CSF.
India ink stain
Most widely used method of staining and observing fungi
Lactophenol cotton or aniline blue wet mount
preserves structures; slides can be made permanent.
Lactic acid
Clearing of specimen to make fungi more readily visible
Potassium hydroxide
Rapid detection of fungal elements.
Potassium hydroxide
Examination of melanin pigment in fungal cell walls
Masson-Fontana stain
Aids differentiation of melanin and hemosiderin pigments
Masson-Fontana stain
Best stain for detecting fungal elements
Methenamine silver stain
Detection of fungi in histologic section
Methenamine silver stain
Examination of secretions for malignant cells
Papanicolaou stain
Stains fungal elements well; hyphae of molds and yeasts can be readily distinguished.
Periodic acid Schiff (PAS) stain
Examination of fungal elements
Saline wet mount
Examination of bone marrow or peripheral blood smears
Wrights stain
Detects Histoplasma capsulatum and Cryptococcus spp
Wright’s stain
Morphologic Form Found in Specimens
Yeastlike
● Spherules
● Yeast and pseudohyphae or hyphae
● Pauciseptate hyphae
● Hyaline septate hyphae
● Dematiaceous septate hyphae
● Sclerotic bodies
● Granules
sensitive method that is difficult to perform
and interpret.
Complement fixation (CF)
simple, cost-effective procedure. Although it is 100% specific, it is relatively insensitive and is not used as a screening tool. This test also requires 2 to 3 weeks to exhibit a positive result.
Immunodiffusion testing
for both antibody and antigen have been used.
These tests are also commonly negative in immunocompromised patients, especially early in the infection
Enzyme immunoassays
Intermediate growers form mature colonies in
6 to 10 days
Slow growers form mature colonies in
11 to 21 days
Rapid growers form mature colonies in
5 days or less
Colony Topography:
Verrucose
Umbonate
Rugose
Colony Texture:
Cottony
Velvety
Glabrous
Granular
Wooly
furrowed or convoluted
verrucose
slightly raised in the center
umbonate
furrows radiate out from the center
rugose
low aerial mycelium resembling a velvet cloth
Velvety
loose, high aerial mycelium
cottony
smooth surface with no aerial mycelium
Glabrous
high aerial mycelium that appears slightly matted down)
Wooly
dense, powdery, resembling sugar granules
Granular
