A multiphasic typing approach to subtype Streptococcus equi subspecies equi.

The research aimed to distinguish between strains of the bacterium Streptococcus equi, which causes abscesses in horses. It used a range of genetic and phenotypic testing methods to compare bacteria isolated from abscesses with bacteria taken from a commercial vaccine, to determine whether the abscesses were caused by the vaccine strain or wild strains of the bacteria.

Research Method

• The researchers used various genotyping techniques, such as enterobacterial repetitive intergenic consensus polymerase chain reaction (PCR), repetitive extragenic palindrome PCR, BOX element PCR, ribotyping, and pulsed-field gel electrophoresis (PFGE). These techniques allowed the researchers to analyze the genetic makeup of the bacteria and compare different strains.
• Alongside genotyping, the researchers also performed phenotypic evaluations using the Biolog GP2 Microplate, a method that uses various substrates to identify bacteria based on their metabolic capabilities.
• In cases where the results from the genotyping and phenotyping did not match, the researchers used a further method: they looked for a specific mutation (a single nucleotide polymorphism) in a gene linked to the physical characteristics of the bacteria. The gene, known as the szp gene, is significant in this context because it is associated with the ability of the bacteria to cause disease.

Results and Conclusion

• The research successfully differentiated between the wild and vaccine strains of the Streptococcus equi bacteria. The PFGE method was particularly useful in distinguishing between different wild strains, while the combination of Biolog and szp sequencing was effective in differentiating the vaccine strain from its wild-type ancestor.
• Interestingly, the study identified a single mutation (the deletion of a guanine residue) located in a control region of the szp gene that appears to be unique to the vaccine strain. This finding strengthens the reliability of the Biolog identification method, with a correlation of 98.5% between the presence of the mutation and a positive Biolog result.
• Overall, this research provides a “multiphasic” approach to the differentiation of Streptococcus equi strains; a method that can be applied in diagnostic, epidemiological, and quarantine situations. This approach allows researchers and veterinary practitioners to accurately identify the source of bacteria causing abscesses in horses, whether it be from a vaccine or a wild strain.