A multiphasic typing approach to subtype Streptococcus equi subspecies equi.

Area of Science:

• Veterinary Microbiology
• Equine Infectious Diseases
• Bacterial Genotyping

Background:

• Equine strangles, caused by Streptococcus equi subspecies equi, leads to abscess formation.
• Differentiating between wild-type and vaccine strains is crucial for diagnosing and managing outbreaks.
• Vaccine-associated infections can complicate diagnostic interpretations.

Purpose of the Study:

• To differentiate wild-type Streptococcus equi strains from vaccine strains in horses.
• To determine the origin of Streptococcus equi isolates from clinical cases versus commercial vaccines.
• To evaluate multiple genotyping and phenotypic methods for strain differentiation.

Main Methods:

• Enterobacterial repetitive intergenic consensus PCR, repetitive extragenic palindrome PCR, BOX element PCR, ribotyping, and pulsed-field gel electrophoresis (PFGE).
• Phenotypic evaluation using the Biolog GP2 Microplate.
• Single nucleotide polymorphism (SNP) analysis of the szp gene regulatory region for ambiguous cases.

Main Results:

• Pulsed-field gel electrophoresis (PFGE) and Biolog successfully distinguished wild-type strains from modified live vaccine (MLV) isolates.
• PFGE allowed further subtyping of wild-type strains.
• Biolog combined with szp sequencing effectively differentiated MLV strains from their wild-type progenitors, noting a conserved guanine deletion in MLV strains.

Conclusions:

• A multiphasic approach combining PFGE, Biolog, and szp sequencing is effective for differentiating Streptococcus equi strains.
• This methodology aids in identifying the source of infection, managing outbreaks, and addressing quarantine concerns in equine strangles cases.
• The conserved genetic marker in vaccine strains provides a reliable identification tool.