Rapid identification of Rhodococcus equi by a PCR assay targeting the choE gene.

The research article focuses on a PCR assay created to rapidly and accurately identify the bacterium Rhodococcus equi, which is a significant pathogen in horses and an emerging one in humans. The PCR test targets the choE gene related to cholesterol oxidase production and is shown to produce specific and accurate results for isolates of R. equi.

Understanding the Study and Its Methodology

• The research article discusses the development of a PCR assay—the Polymerase Chain Reaction technique—which allows certain gene sections to be amplified for easier detection and identification. The assay targets the choE gene that encodes cholesterol oxidase, an enzyme produced by R. equi and other actinomycetes.
• The R. equi is a problematic bacterium in horses and can cause severe diseases in humans as well. The identification of R. equi is crucial, but traditional techniques can be inaccurate leading to misclassification.
• A panel of 132 strains initially identified as R. equi and 30 isolates of non-R. equi actinomycetes were used to assess the choE-based PCR assay. In the process, a specific DNA fragment relating to the choE gene was amplified and observed.

Findings and Results

• From the panel, the PCR assay generated the expected 959 base pairs amplicon with R. equi isolates only. This means that the assay was successful in specifically identifying R. equi bacteria.
• Additional testing and sequencing on 20 PCR-positive isolates confirmed the findings, highlighting the high precision of the choE-based PCR.
• However, three out of the 132 strains originally classified as R. equi lacked the choE gene. Upon further examination of their 16S RNA gene sequences, it was determined that they belonged to different bacterial species—Dietzia maris, Mycobacterium peregrinum, and Staphylococcus epidermidis.
• When examining the ATCC 21387 strain of Brevibacterium sterolicum, the choE-based PCR also produced a 959-bp amplicon, similar to that of R. equi. This instance suggested that ATCC 21387 could instead be considered as an R. equi isolate.

Implications

• This choE gene-based PCR assay allows for a quick and reliable identification of R. equi. Given the health risk posed by the bacterium, particularly in horses and humans, this tool could have significant implications in medical and veterinary contexts.
• The authors note that the high degree of conservation of the choE gene across R. equi isolates, which means this method offers robust specificity when identifying R. equi bacteria.
• The study also underlines the potential flaws with traditional classification methods, given that three out of 132 strains were incorrectly identified as R. equi, emphasizing the need for precise diagnostic tools.