Tracing outbreaks of Streptococcus equi infection (strangles) in horses using sequence variation in the seM gene and pulsed-field gel electrophoresis.

This research focuses on the use of genetic variation found in the Streptococcus equi bacterium’s SeM protein to trace outbreaks of strangles, a serious respiratory disease in horses. The paper finds that sequencing the seM gene of the bacterium produced results that closely agreed with those obtained through pulsed-field gel electrophoresis, a common method of bacterial strain differentiation.

Identification of S. equi Strains

• This research explores a new approach to differentiating between genetically similar strains of the Streptococcus equi bacterium, which causes strangles, a severe respiratory disease in horses.
• Traditional methods to differentiate the bacterium’s strains have been unsuccessful due to their high genetic homogeneity.
• The researchers focused on the bacterium’s M-protein, SeM, specifically its variable N-terminal region, as a target for strain differentiation through gene sequencing.

Study Methodology

• The study genetically characterized 60 S. equi strains derived from 32 strangles outbreaks in Sweden between the years of 1998-2003 and 2008-2009.
• This characterization was performed through sequencing the SeM protein gene (seM), and by pulsed-field gel electrophoresis (PFGE).

Key Findings

• The Swedish S. equi strains belonged to 10 different seM types, five of which hadn’t been previously identified.
• Most of the strains were identical to or highly similar to strains implicated in strangles outbreaks in the UK.
• Outbreaks in 2008/2009 that shared the same seM type were connected by geographical location or type of horse (racing stables).
• SeM gene sequencing results were generally congruent with those from PFGE, implying that the two methods are relatively comparable in their ability to differentiate S. equi strains.

The Implications of the Research

• The study suggests that seM sequencing as an epidemiological tool is supported by the agreement observed between it and PFGE results – the existing method for bacterial strain differentiation.
• The authors also argue that sequencing of the SeM protein gene appears to be more sensitive than PFGE in discerning different strains of S. equi.
• This discovery could help in tracing the source of strangles outbreaks and potentially in developing treatment strategies.