General concepts in Lab diagnosis Flashcards
Surface area: Petri dish
Large (7,500mm2)
Surface area: Test tube
Small (1,500mm2)
Oxygen supply: Petri Dish
Good
Oxygen supply: Test tube
Poor
Rate of drying: Petri Dish
Relatively fast
Rate of drying: Test tube
Relatively slow
Security of closure: Petri Dish
Poor (lid is easily displaced)
Security of closure: Test tube
Good
Probability of dissemination: Petri Dish
Relatively large
Probability of dissemination: Test tube
Relatively small
Detection of mixed culture: Petri Dish
Relatively easy
Detection of mixed culture: Test tube
Relatively difficult
Incubation of Mold forms
25oC to 30oC
Incubation of Opportunistic and dimorphic organisms
30oC
Incubation of Conversion to yeast phase for dimorphic fungi
25oC to 37oC
Rapid growers
< 5 days
Saprobes, opportunistic fungi, yeast
Intermediate growers
6 - 10 days
Subcutaneous & opportunistic fungi, dermatophytes
Slow growers
> 11 days
Systemic & subcutaneous fungi
Appears leather-like, or waxy little mycelium, seems to merge with the agar
Glabrous
Resembles plush or suede, short aerial hyphae of equal length
Velvety
Resembles colonies of other Staphylococcus spp. (formerly CoNS), “bacteria like” but more dry and dull (waxy-pasty). No aerial mycelium, with a delicate fringe around the colonies in BAP
Yeast like
Wooly or “Floccose”, large quantities of long aerial hyphae that becomes entangled and may fill the entire petri dish
Cottony
Powdery due to heavy conidiation or sporulation, has even hyphae and abundant conidia
Granular
Presence of radial groves from the center of the culture toward the rim
Rugose
Random folds (long, short, parallel at right angles or combination)
Folded
Have central depression (concavity) surrounded by raised edges. Resembles S. pneumoniae colonies
Crateriform
Have many warts or rough knobs on the surface
Verrucose
Brain-like convolutions
Cerebriform
Four methods of Microscopic evaluation of growth in culture
Tease mount
Scotch tape method
Slide culture
Dalmau method
Recommended for studying yeast morphology. It is performed by using one-fourth or one-third of a cornmeal-Tween 80 agar plate for each organism.
Dalmau Method
FOur ways of Preservation of cultures
storage in water
freezing
mineral oil overlay
lyophilization
Conidia and spores form a fresh culture are washed off in sterile water and placed in labelled vials
Storage in water
Labelling glass tubes with a screw-capped and placed in a freezer
Freezing
Layering an entire slant with mineral oil, capping the tube tightly and storing at room temperature
Mineral oil overlays
Freeze drying with the use of special equipment
Lyophilization
temperature in freezing preservation of culture
-70C
Aspergillus spp. immunologic assay
CIE, FEIA, EIA
Antibod(ies) Antigen(s) detected in Aspergillus spp.
Aspergillus IgG
helpful in diagnosing allergic bronchopulmonary aspergillosis (ABPA), aspergilloma, and Chronic cavitary aspergillosis
Aspergillus IgG
Blastomyces spp. assay
Commercial kits
Blastomyces spp. antibodies or antigens detected
Antigens (eg., A Ag, WI1 Ag)
limitation of Blastomyces spp. immunologic detection
lack of sensitivity due to cross- reactivity with dimorphic fungi
Candida spp. immunologic assay
EIA
Candida spp. Antibod(ies) Antigen(s) detected
Mannan Ag
Candida IgG, IgM, & IgA
Cryptococcus spp. assay
EIA
Cryptococcus spp. Antibod(ies) Antigen(s) detected
Cryptococcus IgG, IgM, IgA
Ag: Glucuronoxylmannan
can be a marker for reactivation of disease in solid organ transplant recipient
Cryptococcus antibodies
A polysaccharide present in the cell wall of many fungi viz., Aspergillus, Candida, Fusarium
1,3-β-D-glucan
Found in the blood of patients with invasive fungal infections, and its ability to activate factor G of the horse-shoe crab coagulation pathways that allows it to be measured and quantified.
1,3-β-D-glucan
1,3-β-D-glucan detection is rarely or not present in
Cryptococcus, Blastomyces, Mucoraceous molds.
Has the ability to detect organisms that are present in small numbers of that cannot be cultured.
Nucleic acid testing
Nucleic acid testing removes the risks associated wit culturing especially for
H. capsulatum
Offers the potential to identify pathogens in biopsy samples that have been formalin-fixed and even wax-embedded.
Nucleic acid testing