The molecular identification of Streptococcus equi subsp. equi strains isolated within New Zealand.

This research article explores the identification and characterization of Streptococcus equi subsp. equi (S. equi) strains infecting horses in New Zealand by using a PCR-based method as well as culture methods. The PCR analysis focused on the amplification of the seeI gene, while strain typing was achieved by sequencing the hypervariable region of the seM gene of S. equi.

Methods Used

• The researchers used diagnostic PCR, which works on the principle of amplifying a specific DNA segment, to identify the S. equi strains. The focus was on the seeI gene of S. equi.
• They examined 168 samples obtained from horses, among which, some showed clinical signs of strangles and others didn’t.
• Besides PCR, the researchers also carried out bacterial culture on selective media for the isolation of β-haemolytic colonies.
• To perform strain typing, the hypervariable region of the seM gene of S. equi was amplified and sequenced.

Research Findings

• Among the 168 samples tested, 35 were positive for S. equi based on the PCR results. Thirty-two of these samples were from horses diagnosed clinically with strangles, while for three samples, clinical information wasn’t available.
• When culture methods were used, successful isolation of S. equi was achieved only with 22 out of 35 confirmed samples.
• The strain typing revealed two new seM alleles of S. equi in New Zealand. The SeM-99 strains were restricted to the North Island, while the SeM-100 strains were found in both North and South Islands.

Conclusions

• The researchers concluded that PCR analysis forms a sensitive and reliable approach for rapid identification of S. equi. It proves to be more efficient than culture methods since it reduces the time required for laboratory confirmation of strangles, a common disease in horses caused by bacteria S. equi.
• PCR is also better at detecting S. equi infections, especially in the carrier animals which generally release a low number of bacteria. This feature of PCR is essential for effective early detection and control of strangles outbreaks.
• Additionally, the implementation of seM molecular typing helped in distinguishing between different bacterial strains, providing valuable insights into the S. equi strains causing disease in the local area.