Molecular vs Serological Diagnosis

Microbiology

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Overview

Pathogen Diagnosis- determining the presence of a pathogenic microorganism.
1. Molecular Diagnosis- sequencing of either the nucleic acids or proteins to determine the presence as well as the evolution of a foreign pathogen.
  1. Genomic testing- uses specific genetic markers (variations in DNA or RNA sequences) unique to species for identification.
    1. ex. Swab test for COVID-19 detects if viral genetic (RNA) material is present in sample.
  2. Proteomic testing-identifies proteins associated with human disease including infectious disease.
    1. ex. Protein markers used to test proteins secreted by Mycobacterium tuberculosis
2. Serological Diagnosis- relies on the body’s immune response (antibody production) to detect a current or past exposure to a pathogen.
  1. Examples of Types of Serological Tests
    1. Agglutination Assay- identifies the presence of an antibody in blood serum by exposing it to the antigen and observing clumping.
      1. Protozoa detection like Visceral leishmaniasis
    2. Precipitation Test- shows the presence of antibodies to a specific antigen by forming a cloudy precipitate in solution.
      1. Detect Fungal infections
    3. ELISA (Enzyme-Linked ImmunoSorbent Assay) uses pathogen antigens to find antibodies in the patient’s blood.
      1. Detect HIV, Lyme Disease
    4. Monoclonal Antibody technique
      1. ex. Detect specific strains of bacterial infections (ex. specific E.coli strain)

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Transcript

Today we’re going to be talking about Molecular versus serological diagnosis.

“In this lesson on pathogen diagnosis, we will cover 2 ways in which we can verify the presence of a pathogen, molecular diagnosis and serological diagnosis.

So when a individual is sick, often times it can be due to the presence of a pathogen that has made its way into the body. When this happens it is sometimes beneficial to pinpoint exact details about the pathogen that is making the individual sick in order to best treat and or prevent the spread of illness. Two different approaches to diagnosing the presence of pathogen are molecular testing and serological testing.

In Molecular diagnostics, the specific sequence of certain biomolecules to known pathogens are screened for. Usually this involves looking for a sequences of Nucleic acids or DNA/RNA found only in that pathogen or a sequence of amino acids specific to a protein of the pathogen.

Molecular diagnostics requires collecting a tissue or blood sample from the patient. From this sample proteomic testing using mass spectrometry can identify the presence of amino acids sequences that are related to certain strains of bacteria, viruses and other pathogens. Additionally Genomic testing can help ID a certain pathogen through DNA fingerprinting.

Another method used to diagnosis someone is called serological testing. Serological testing relies on the human body’s immune system’s response to the presence of a foreign body. Invading pathogens tend to wear certain disguises on their outer membrane, we refer to this disguise or what the “bad guy” is wearing as an antigen. When the body is exposed to foreign antigens it will eventually respond in order to fight back by making antibodies, which are specific to the antigen and in turn block the bad guys preventing them from invading more cells in the body. In this diagram “B” we will say is pointing to the antigen of the “bad guy” and A is the antibody made by the immune system to block and prevent further infection. This type of testing tests for the presence of antibodies. This can be limited perspective however, as antidoes could be around from a vaccine or perhaps even after the individual is no longer infected.

Serological testing can take place in a number of different ways, depending on the situation. Agglutination is testing for clumping by exposing the patient’s sample to various antigens to test for the presence of an antibody. Precipitation is a similar test but in solution that looks for a precipitate to form that would make the solution cloudy do to the “clumping”. ELISA is a method of tagging an antigen that marks the presence of an antibody (used in Western blots, testing for HIV). Monoclonal antibody is a technique in which antodies are produced in order to test for a specific antigen.

In summary there are two main ways to test for the presence of a pathogen. Molecular diagnostics that test for nucleic acids and proteins specific to the pathogen strain and serological diagnostics that tests for antibodies produced in response to exposure at some time.

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