Bacteriology lab

Question 1

What are the commonest diagnoistics techniques when testing (for) a bacterial infection?

Answer 1

1. Cultivation
   
   1. sterile site (blood CSF)
   2. non-sterile site
2. Serology
3. Molecular Tequniques
4. 1)Antimicrobial Susceptibility Testing

Question 2

What happens if a blood culture was tested positive for bacterial infection?

Answer 2

Not good–> normally no pathogens should be in blood

But then: Identification of problem

1. Gram stain
2. coagulation test? (Staphylococcus)
3. hamolytic streptococcus testing etc.

Question 3

Explain the use of agar plates in cultivation of bacterial cultures

Answer 3

Every bacteria has a special agar plate to maximise growth –> important to ask for the right test to get the important results!

Question 4

What is the Minimum Inhibitory Concentration of a drug?

Answer 4

Minimal concentration of antibiotic needed to kill pathogens –> prevention of over administration of antibiotics and resistance

Question 5

How is Miniumum inhibitory concentration tested for in lab conditions?

Answer 5

Strips with different antibiotic concentrations –> see to where the bacteria grows

Question 6

Why is it important to give a specific differential diagnosis when requesting a bacteriology lab?

Answer 6

There are many unsterile sites in body–> soooo many bacteria, it is unlikely to find what you are looking for when you don’t have a specific clue

Question 7

How does a ideal antigen testing look like to confim a bacterial diagnosis?

What does it more realistically look like?

Answer 7

First test (before exposure): negative test

Had disease

Positive serum antibody test

Question 8

Always include clinical information including travel history on requests.

Contact Infectious Diseases or Microbiology early if you require advice.

Try and send samples for culture prior to starting antibiotics if possible.

Question 9

Why is it important to try to obtain a blood sample before administration of antibiotic in a suspected bacterial infecion?

Answer 9

Because even if bacterium is resistant to antibiotic, it might still be killed in the sample –> more difficult to detect infection!

Question 10

Where might a non-sterile sample be taken in a bacteriology lab?

Answer 10

Basically in any non-sterile site:

1. Pharymx, nose, mouth etc,
2. GI tract
3. vagina
4. skin
5. etc.

Question 11

Explain the limitation of a test for a disease with low prevalence

Answer 11

At low prevalence the positive predicted value will be low (because many people who don’t have the disease will be tested–> high number of false positives) –> unnecessary, not smart to do tests randomly, if you don’t have a differential diagnosis etc.