Diagnostics Flashcards
______= true +/ (true pos. + false -)
Sensitvity
_______ = true neg. / true neg. + false pos)
specificity
What are the steps for ruling out Syphillis.
For ruling out syphilis
• Rapid plasma reagin (RPR) test •Venereal Diseases Reference Laboratory(VDRL) test •These tests have a low false negative rate (very sensitive)
Follow up a positive RPR or VDRL test to confirm syphilis (need a very specific test)
t/f: One can diagnos infections by microscopy
true
What two stains are used in Diagnosing infections by microscopy
Gram stain and acid-fast stain
• Apply the primary stain (crystal violet) to a
heat-fixed smear of bacteria. •Add a trapping agent (or mordant) (Gram s
iodine). •Decolorize with acetone or alcohol. Thick
peptidoglycan layer of Gram positives keeps
crystal violet-iodine complex trapped within
cells. This step must be done quickly
(seconds); if too long the crystal violet will be
washed from both Gram-negatives and Gram
positives). •Counterstain with safranin to stain
decolorized cells.
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Gram Stain
•Apply the primary stain (fuschin) + mordant
(carbolic acid) (combination is called
carbolfuchsin) to a heat-fixed smear of
bacteria. Place piece of absorbant paper
soaked with carbolfuchsin over the smear and
heat the slide to drive the stain+mordant into
cells.
•Decolorize with dilute acid in alcohol. The
carbolfuchsin will wash out of most cells, but
not those with high levels of mycolic acid in
their membranes (e.g. mycobacteria)
•Counterstain with methylene blue to stain
decolorized cells.
Acid fast staind
Direct Fluorescent Antibody (DFA) test
• Antibody-based identification
cu lturing involves use of numerous kinds of growth media
can provide preliminary information about biochemical nature of bacterium additional biochemical tests used following isolation
most bacteria
rickettsias, chlamydiae, and mycoplasmas
identified with special stains, immunologic tests, or molecular methods
some bacteria are not routinely cultured
A _____ ______ is prepared by the addition of specific substances to a culture medium that will premit growth of one group of bacteria while inhibiting growth fo some other groups.
selective media
the incorporation of certain chemicals into a medium may result in diagnostically useful growth or visibile changes in the medium after incubation.
differential media
the additions of blood, serum, with support the growth of many fastidious bacteria. these media are used primarily to isolate bacteria from cerebralspinal fluid, plueral fluid, sputum, and wound abseses.
enrichment media.
____ _____ are used to test bacteria for particular metabolic activities, products, or requirements.
characteristic media
• only done by CDC and certain labs
• based on specificity of phage surface molecules for host
cell surface molecules
• phagovar
– bacterium with sensitivity to certain collection of phage types
Bacteriophage Typing
