Evaluation of a monoclonal antibody-based colony blot test for rapid identification of virulent Rhodococcus equi.

The researchers have developed a quick and reliable test, using a certain monoclonal antibody, for identifying strains of Rhodococcus equi that are harmful. The accuracy of this test was validated by applying it to samples taken from various sources in a horse-breeding environment and comparing the results to more conventional testing methods.

Creating the Monoclonal Antibody

• The researchers began by creating a monoclonal antibody (MAb 10G5) that is capable of identifying specific antigens – substances that trigger an immune response – associated with the harmful or ‘virulent’ strains of the bacteria Rhodococcus equi.
• These particular antigens were of a certain size (15-17 kilodaltons) and were identified as being directly related to the bacteria’s virulence, or ability to cause disease.

Developing the Colony Blot Test

• They then used this monoclonal antibody to develop a quick test, called a ‘colony blot enzyme-linked immunosorbent assay’, for identifying virulent strains of R. equi.
• This type of test provides a quick and visual readout, allowing for rapid identification of the virulent strains of this bacteria.

Evaluating the Test

• The validity of this new test was assessed by using it to test a large number of isolates, or pure samples, of R. equi derived from the manure of horses (both foals and dams) as well as from soil taken from horse-breeding farms in the Hokkaido region.
• The results obtained from this antibody-based test were compared with those of more traditional testing procedures, which involved analyzing the isolates’ plasmid profiles through gel electrophoresis – a technique that separates DNA fragments based on their size.

Results and Conclusion

• The comparison of results demonstrated a high level of agreement, indicating that the new antibody-based test was reliable and could accurately identify those strains of R. equi that posed a threat.
• In particular, majority of the isolates that showed positive results with the new test also contained, as confirmed by the traditional testing method, plasmids – small, circular pieces of DNA – that were associated with virulence.
• Conversely, a random selection of isolates that showed negative results with the test did not contain these virulence plasmids.

This study’s findings support the use of this new test as a convenient and reliable method for identifying harmful strains of R. equi in equine environments.