Use of a PCR assay for Taylorella equigenitalis applied to samples from the United Kingdom.

The study investigates the use of a polymerase chain reaction (PCR) assay for detecting Taylorella equigenitalis, the bacterium causing contagious equine metritis in horses, in samples from the United Kingdom. The PCR approach was deemed necessary due to the long incubation period for laboratory culture of T. equigenitalis and the potential insensitivity of standard tests.

Overview of Contagious Equine Metritis

• The research paper starts by describing contagious equine metritis, which is an inflammation of the endometrium in mares caused by the infection of the bacterium Taylorella equigenitalis (also known as the contagious equine metritis organism or CEMO).
• Although most infected horses recover without issues, some mares can become asymptomatic long-term carriers of the bacterium.
• The bacterium can also infect stallions, although they remain symptomless, and both carrier mares and infected stallions can spread the bacterium during mating.
• The paper notes that the disease has been effectively controlled in the United Kingdom and other countries through the use of urogenital swabs and testing to demonstrate freedom from T. equigenitalis infection before mating.

Need for a New Detection Method

• The study highlights that the standard culture method for detecting T. equigenitalis has some limitations, including a long incubation period and potential insensitivity due to the poor selective capacity of the culture media. This insensitivity might lead to false negatives, i.e., an infected horse testing negative due to the bacterium not being detected.
• These limitations led the researchers to consider the use of a polymerase chain reaction (PCR) test, which is a molecular technique used for the detection and amplification of specific DNA sequences. In this case, the PCR was formulated to target unique sequences in the 16S RNA gene of T. equigenitalis.

Findings from the PCR Test

• The paper found that the PCR tool appeared highly specific for T. equigenitalis when tested against a range of bacteria grown in the lab. Despite this, up to 35% of swabs taken from healthy horses in the Netherlands tested positive for T. equigenitalis via PCR, even though no bacterium was detected through the standard culture method.
• The researchers also noted that the PCR’s detection rate substantially improved when target DNA was extracted from bacterial growth on CEMO culture media that was inoculated with swabs and left to incubate for a few days.
• This indicates that the bacterium responsible for the positive PCR test could grow on the specific CEMO culture medium. However, the growth might be too minimal for visible colonies to form, or it could be overwhelmed by other bacteria, explaining why some of the PCR-positive samples were culture-negative.