IA. General Microbiology | 20. Diagnosis of the infectious diseases.

Question 1

What are the 3 bacterial Typing Methods?

Answer 1

1. Phage typing
2. Serotyping
3. Molecular typing (genotyping, genetic fingerprinting)

Question 2

I. Phage typing
1. What are the features of phage typing?

Answer 2

• bacterium isolated from the patient is smeared onto the surface of an agar plate (bacterial lawn is made), then different bacteriophage
suspensions are added (dropplets of different bacteriophages are added, see the picture below)
• if the particular bacteriophage is able to infect the given bacterium, then the bacterium dies, won’t proliferate (empty circles: plaques)
• by using multiple different types of phages, the unique constellation of the given bacterium (phage-type) could be determined
1. Species types made based on their sensitivity to bacteriophages
2. Old method

Question 3

II. Serotyping
1. What are the features of Serotyping?

Answer 3

• Serotyping: subspecies groups are made based on serological differences: differences in antigenicity
• Method= slide agglutination
  +) Reagent (Ab)+ saline + bacterium(Ag)= clumps (positive) or homogenous (negative)

Question 4

III. Molecular typing (genotyping, genetic fingerprinting)
1. What are the 3 methods of Molecular typing?

Answer 4

1. PFGE (pulse field gel electrophoresis)
2. Typing based on sequencing
3. MALDI-TOF

Question 5

III. Molecular typing (genotyping, genetic fingerprinting)
2. What are the features of PFGE (pulse field gel electrophoresis)?

Answer 5

1. DNA of bacteria cut, fragments separated in argos gel using changing electric filed, DNA fingerprints with specific pattern are seen
2. Maximum 1 band difference= same strain
3. Important for investigation of epidemics

Question 6

III. Molecular typing (genotyping, genetic fingerprinting)
3. What are the features of Typing based on sequencing?

Answer 6

1. Comparing sequence of genes present in every strain of the species
2. Number of difference, mutations= how closely they are related
3. Important for epidemiology

Question 7

III. Molecular typing (genotyping, genetic fingerprinting)
4. What are the features of MALDI-TOF?

Answer 7

1. Rapid identification of bacteria based on protein markers
2. Pulsed laser irradiates the bacterial colonies => released molecules are separated
   based on weight and charge
3. Pattern compared to standard bacterial database → species identification