micro 20.3

Agglutination

The process in which antibodies cause cells or particles to clump together.

Types of particles agglutinated by antibodies

Cells such as bacteria and red blood cells, as well as particles such as antigen-coated latex beads.

Uses of agglutination assays

To detect the presence of specific antibodies or antigens.

Advantages of agglutination assays in clinical testing

They are generally quick and easy to perform.

Common performance locations for agglutination assays

On a glass slide or in a microtiter plate.

Microtiter plate

A plate containing an array of small wells that hold small volumes of reagents for performing multiple tests simultaneously.

Direct agglutination assay

An assay in which the cells or particles carrying the antigen directly agglutinate when antibodies bind to them.

Important direct agglutination method developer

Rebecca Lancefield, working with A. R. Dochez and Oswald Avery.

Bacterial protein identified by Lancefield's antibodies

The M protein found on streptococci.

Importance of M protein to streptococci

It is a virulence factor necessary for the bacteria's ability to cause strep throat.

Lancefield's research on M proteins

Demonstrated that different strains of the same streptococcal species can express different versions of M protein.

Reason for multiple strep throat occurrences

Different strains of streptococci can have different antigenic versions of M protein, so immunity to one strain may not protect against another.

Serovars definition

Strains of a microorganism that are differentiated based on their antigenic properties, often using specific antisera.

Lancefield's classification of beta-hemolytic streptococci

Based on antigenic differences in group-specific polysaccharides in the bacterial cell wall.

Importance of identifying serovars during outbreaks

Some serovars can cause more severe disease than others.

Indirect agglutination assay

An assay in which antibodies are attached to inert latex beads, and agglutination of the beads indicates antibody binding to another antigen.

Another name for an indirect agglutination assay

A latex fixation assay.

Purpose of latex beads in indirect agglutination assays

They make the agglutination reaction easier to see.

Detection capabilities of indirect agglutination assays

Either specific antibodies or specific antigens.

Detection of antibodies using antigen-coated latex beads

The beads are coated with the antigen of interest; if the patient's serum contains antibodies against that antigen, the antibodies cross-link the beads and cause agglutination.

Most commonly detected antibody class with latex beads

IgM antibodies.

Effectiveness of IgM at causing agglutination

Its structure provides maximum cross-linking between antigen-coated particles.

Rheumatoid factor (RF) definition

IgM antibodies that bind to the patient's own IgG.

Detection of rheumatoid factor via latex agglutination test

IgG-coated latex beads are mixed with patient serum; rheumatoid factor binds the IgG and causes the beads to agglutinate.

Detection of soluble antigens using indirect agglutination test

Specific antibodies are attached to latex beads and mixed with the patient's serum; if the target antigen is present, it cross-links the antibody-coated beads, causing agglutination.

Type of antibodies commonly attached to latex beads for soluble antigens

Monoclonal antibodies (mAbs).

Widal test diagnostic purpose

To diagnose typhoid fever.

Organism detected by the Widal test

Salmonella enterica subspecies typhi.

Advantages of the Widal test

It is rapid, inexpensive, and useful for monitoring the extent of an outbreak.

Major limitation of the Widal test

It is less accurate than tests that involve culturing the bacteria and can produce false-positive and false-negative results.