Diagnostic Microbiology non-culture based diagnostics

Question 1

What are the limitations to culture diagnosis?

Answer 1

Although culture remains the standard diagnosis of infectious agents
> Cannot be used for agents that cannot be cultured or difficult to culture
>Takes a long time for some organisms to grow eg mycobacterium
>Some cultures lack sensitivity eg blood cultures are only 50% sensitive for fungi culture
> Some organisms lose viability before the organism arrives for culture at lab eg anaerobes
>

Question 2

Which samples can be used for non-culture diagnosis

Answer 2

*blood, tissue and urine, and other body fluids

Question 3

What is the advantage of non-culture based diagnosis

Answer 3

*One does not need a sample from from the site of infection

Question 4

list the 3 types of non-culture diagnosis

Answer 4

1. Antigen detection
2. Molecular test
3. Immunoassy

Question 5

Serology is an example of a immunoassay.

What is a serology and how can the results be interpreted ?

Answer 5

*A scientific diagnostic examination of the blood serum especially with regards to the immune system to pathogen.

IgM : first to be produced in a response and have a short half life whereas IgG are mature antibody response and develops later and last longer

Question 6

What are the antibody tests uses

Answer 6

• Document exposure to infection agent
• evaluate protection against pathogen
• Diagnose reason for transfusion rejection
• Monitor course of infection
• diagnose an allergy
• diagnose an auto-immune condition

Question 7

Give 4 examples of antigen detection methods

Answer 7

1. Agglutination : Latex particles coated with antigen and when combined with antibodies ,they form clumps
2. Flocculation : Antigen particles combine with antibodies result in a large clumps
3. Haemagglutination : Clumping together of RBC in the presence of antigens
4. Elisa : Antigen -antibody reaction. Antigens are labeled by a fluorescence that can be read by spectrometer
5. LATERAL FLOW ASSAY
   * Same principle as Elisa .Runs the liquid sample along the surface of a pad with reactive molecules that show a visual pos or neg results eg pregnancy tests

Question 8

When can we use an antigen detection

Answer 8

*It is used to detect components of a pathogen where a culture cannot be performed ,poor sensitivity or long turn around time

Question 9

How are molecular tests used to detect

Answer 9

*By detecting the organism’s molecules in the human body .The molecule commonly used for such diagnosis are nucleic acids

Question 10

Uses of molecular tests

Answer 10

• Diagnosis of diseases
• Detection of resistance
• surveillance
• biome studies
• disease monitoring
• Molecular epidemiology