9 - Diagnosing Infections Flashcards

1
Q

How to make a specific aetiological diagnosis of infection

A

1) Demonstrate organism, component or product
2) Isolate the micro-organism (“gold standard”)
3) Demonstrate a serological response

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2
Q

Solid phase assay

A

Immobilise antigen of interest on solid phase.

Wash with known antibody with fluorescent tag.

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3
Q

How could the lineage of tumour cells be determined?

A

With immunohistochemistry.

Stain with tagged antibodies against specific cell surface markers.

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4
Q

Capture assay

A

Immobilise antibody of known specificity on solid phase.
Wash with sample.
Wash with tagged antibody of known specificity.

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5
Q

Nucleic acid detection methods

A

1) Hybridisation

2) PCR

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6
Q

Hybridisation

A

Fluorescently-tagged DNA sequence added to ssDNA sequence.

If it hybridises, DNA sequences are complementary

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7
Q

In situ hybridisation

A

Fluorescently-tagged DNA sequence is added to tissue section.
EG: Detecting HER2 in breast cancer tissue

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8
Q
Using PCR to identify the causative agent of bacterial meningitis in children
1)
2)
3)
4)
A

1) Testing for Strep pneumoniae, Haemophilus influenzae, Neisseria meningitidis.
2) Reverse primers are the same, unique forward primers
3) Fragment lengths for each bacterium will be different.
4) Run fragments on a gel, can tell which bacterium is possibly present by length of fragment.

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9
Q

Issue with PCR identification of bacteria

A

All you can really say is that there is a DNA fragment of similar length to that of suspected orgamism

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10
Q

How to tell if a serological response is new or old
1)
2)

A

1) Test antibody titres at 2 points in time, and see if titres are rising. 4-fold titre rise is diagnostic
2) High IgM titres are indicative of recent infection

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11
Q

Anti-IgM assays

A

1) Known antigen fixed to solid phase. Wash with patient’s serum. Wash with anti-human tagged antibody
2) Anti-IgM antibody fixed to solid phase. Wash with patent’s serum. Wash with known antigen of interest. Wash with anti-antigen tagged antibody.

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