5.58 Flashcards

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1
Q

For ruling out syphilis (2)

A

•Rapid plasma reagin (RPR) test
•Venereal Diseases Reference
Laboratory(VDRL) test

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2
Q

•Venereal Diseases Reference
Laboratory(VDRL) test
•These tests have a low

A
false
negative rate (very sensitive)
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3
Q

Follow up a positive (2) test
to confirm syphilis (need a very
— test)

A

RPR or VDRL

specific

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4
Q

Diagnosing infections by microscopy

A

• Direct microscopic examination of clinical specimens

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5
Q

• Direct microscopic examination of clinical specimens

Syphilis -

A

spirochetes observed in scrapings of lesions

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6
Q

Diagnosing infections by microscopy

• Stains

A

Gram stain and acid-fast stain

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7
Q

Gram stain and acid-fast stain (3)

A
  1. Bacteria in normally sterile body fluid (CSF, pleural fluid, urine)
  2. Staining properties part of larger effort at diagnosis
  3. Actual diagnosis (sometimes)
    e.g. Gram-negative diplococci in leukocytes of CSF
    = meningococci (agent of meningitis)
    e.g. acid-fast bacteria in smears of sputum
    = Mycobacterium tuberculosis
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8
Q

Gram stain

4

A

•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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9
Q

acid-fast stain (Ziehl-Neelsen method)

3

A

•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.

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10
Q

Gram-negative diplococci in urethral pus =

A

gonococci (gonorrhea) (only see counterstain)

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11
Q

• Antibody-based identification -

A

Direct Fluorescent Antibody (DFA) test

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12
Q

Diagnosing infections by culture

most bacteria:

A

culturing involves use of numerous kinds of growth media
can provide preliminary information about biochemical nature of bacterium
additional biochemical tests used following isolation

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13
Q

Diagnosing infections by culture

some bacteria are not routinely cultured

A

rickettsias, chlamydiae, and mycoplasmas

identified with special stains, immunologic tests, or molecular methods

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14
Q

Open-ended sampling versus looking for a particular pathogen

A

Pus specimen from brain abscess

Throat culture examined for
Streptococcus pyogenes

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15
Q

selective media

A

prepared by the addition of specific substances to a culture medium that will permit growth of one group of bacteria while inhibiting growth of some other groups

ex. SS

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16
Q

differential media

A

incorporation of certain chemicals into a medium may result in diagnostically useful growth or visible change in the medium after incubation

ex. EMB

17
Q

enrichment media

A

the addition of blood, serum will support the growth of many fastidious bacteria. these media are used primarily to isolate bacteria from CSF, pleural fluid, suputum, and wound abscesses

18
Q

characteristic media

A

characteristic media are used to test bacteria for particular metabolic activities, products or requirements

ex. urea broth is used to detect the enzyme urease. some enteric bacteria are able to break down urea, using urease, into ammonia and co2

19
Q

Bacteriophage Typing
• only done by
• based on specificity of

A

CDC and certain labs
phage surface molecules for host
cell surface molecules

20
Q

Bacteriophage Typing

• phagovar

A

– bacterium with sensitivity to certain collection of phage types

21
Q

Measuring the antibody response to infection

A

patient serum incubated with antigen on solid support
unbound ab washed away
enzyme labeled anti immunglobilin binds to patient ab bound to the antigen on the solid support
amount of enzyme activity is measured

22
Q

Diagnosing infection by detecting microbial macromolecules (4)

A
  1. Detecting microbial antigens
  2. Nucleic acid amplification (polymerase chain reaction (PCR))
  3. Microarrays
  4. Next generation sequencing
23
Q

Tests for SARS-CoV-2 Virus (COVID-19)

A

Real-time reverse transcription-polymerase chain reaction (rRT-PCR) or
sequencing of reverse transcribed SARS-CoV-2 RNA genome regions
Use nasal swab or saliva
Sensitive and specific

24
Q

Diagnosing HIV infection

Standard tests detect (2)

A

HIV antigen and anti-HIV antibodies

25
Q

Tests for Zika Virus

For symptomatic persons suspected for Zika virus infection

A
  1. Real-time reverse transcription-polymerase chain reaction (rRT-PCR)
    Use serum or urine collected within 2 weeks after symptom onset.
    A positive rRT-PCR result confirms Zika virus infection and no
    additional testing is indicated.
    Sensitive and specific but subject to limited time window
26
Q

Tests for Zika Virus

For symptomatic persons suspected for Zika virus infection

A
  1. A negative rRT-PCR result does not exclude Zika virus infection and
    serum should be analyzed by IgM antibody (serological) testing.
    Sensitive with longer time window but not as specific
    cross-reactivity with other flaviviruses