Slide 1
Growth and genetic detection differ
A culture tries to grow an organism from a sample. A molecular test can look for a selected genetic sequence instead.
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Both begin with sampling, but they do not ask exactly the same question. Evidence that a target sequence is present differs from demonstrating growth under laboratory conditions.
Slide 2
Culture needs suitable conditions
A culture supplies conditions in which selected microbes may multiply. Detectable growth can take time and depends on the organism.
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Specimen type and collection quality matter. An organism introduced during collection can confuse interpretation, while prior treatment or unsuitable conditions may prevent growth from a relevant organism.
Slide 3
Amplification makes a target detectable
Polymerase chain reaction (PCR) repeatedly copies a selected region of DNA, the genetic material, so that a small starting amount becomes easier to detect.
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For an RNA target, a reverse-transcription step can first make a DNA copy. The method is therefore adapted to the material being measured rather than directly copying every kind of molecule in the same way.
Slide 4
A positive result needs a question
Detecting genetic material does not always establish that a microbe is alive or causing current symptoms. The result must match the clinical question.
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PCR methods also have uses outside infection testing, including investigation of genetic changes. The technique describes a way to amplify information, not a diagnosis unique to one disease.
Slide 5
Methods can complement one another
Culture and molecular testing can provide different useful evidence from the same illness. One method does not universally replace the other.
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A cultured isolate may support tests of susceptibility to medicines. A targeted molecular result may be available sooner, but speed and the range of questions answered are separate properties.
Sources
- Bacteria Culture Test
MedlinePlus Medical Test
- PCR Tests
MedlinePlus Medical Test