Diagnostic Methods

Question 1

Know the difference between conventional differential media and selective media:

Which can each grow? How do they identify organisms?

Answer 1

Differential media grows organisms indiscriminately. It identifies organisms macroscopically similar organisms typically through a color change in colonies or precipitate around colonies. Selective media contains ingredients that enhance the presence of desired organisms and this inhibits the growth of undesired organisms and this is also how it would identify which organisms to grow.

Question 2

Know about enrichment media:

What are some examples of what it can grow?

Answer 2

Enrichment media allows for fastidious (picky) organisms to grow quickly. This is accomplished by the presence of specific nutrient additives. An example would be chocolate agar and it can grow fastidious bacteria such as Franciscella, Neisseria, and Haemophilus

Question 3

Know about rapid test media. When would you use this? Benefits over conventional media?

Answer 3

Rapid test media would be used when you want to grow bacteria quickly; 18 hours or less of incubation to show results. This media is beneficial because it is cheaper than regular media and it can be differential or selective.

Question 4

Molecular techniques:

Know the mechanism behind PCR/RT-PCR testing. Know how the test can be adapted to diagnose specific organisms.

Answer 4

PCR tests takes one strand of template DNA and utilizes the high efficiency of polymerase to synthesize limitless quantities of targeted nucleic acid sequences. It is used to identify unknown bacterial isolates. It’s good because it’s cheap, quick, specific, and only needs a small sample. It is bad because DNase can degrade the product and DNA is unstable. A RT-PCR uses reverse transcriptase to amplify mRNA target to produce cDNA (complementary DNA), which is then amplified by PCR. It is good because the protocol is specific and efficient. It is bad because RNase can degrade the product and RNA is very unstable.