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Journal of clinical microbiology2006; 44(2); 480-486; doi: 10.1128/JCM.44.2.480-486.2006

Sequence variation of the SeM gene of Streptococcus equi allows discrimination of the source of strangles outbreaks.

Abstract: Improved understanding of the epidemiology of Streptococcus equi transmission requires sensitive and portable subtyping methods that can rationally discriminate between strains. S. equi is highly homogeneous and cannot be distinguished by multilocus enzyme electrophoretic or multilocus sequence-typing methods that utilize housekeeping genes. However, on sequence analysis of the N-terminal region of the SeM genes of 60 S. equi isolates from 27 strangles outbreaks, we identified 21 DNA codon changes. These resulted in the nonsynonymous substitution of 18 amino acids and allowed the assignment of S. equi strains to 15 distinct subtypes. Our data suggest the presence of multiple epitopes across this region that are subjected to selective immune pressure (nonsynonymous-synonymous substitution rate [d(N)/d(S)] ratio = 3.054), particularly during the establishment of long-term S. equi infection. We further report the application of SeM gene subtyping as a method to investigate potential cases of disease related to administration of a live attenuated S. equi vaccine. SeM gene subtyping successfully differentiated between the vaccine strain and field strains of S. equi responsible for concurrent disease. These results were confirmed by the development and application of a PCR diagnostic test, which identifies the aroA partial gene deletion present in the Equilis StrepE vaccine strain. Although the vaccine strain was found to be responsible for injection site lesions, all seven outbreaks of strangles investigated in recently vaccinated horses were found to be due to concurrent infection with wild-type S. equi and not due to reversion of the vaccine strain.
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Publication Date: 2006-02-04 PubMed ID: 16455902PubMed Central: PMC1392674DOI: 10.1128/JCM.44.2.480-486.2006Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The study focuses on identifying distinct strains of Streptococcus equi – the bacterium that causes strangles in horses – to determine the origin of disease outbreaks. Researchers observed 21 DNA codon changes in a specific gene, allowing them to discriminate between 15 different subtypes of the bacteria. The study also investigated potential disease cases related to a live vaccine, successfully differentiating the vaccine strain from wild strains. The results indicated that the vaccine strain could cause injection site reactions but was not responsible for disease outbreaks.

Identification of Streptococcus equi Strains

  • The researchers wanted an improved method to identify strains of the bacterium Streptococcus equi, which causes the equine disease strangles. Understanding the exact strains involved in outbreaks can inform more effective treatment and prevention strategies.
  • This bacterium is highly similar across strains, making it difficult to distinguish between different types using conventional methods. Hence, the researchers conducted a sequence analysis of the N-terminal region of the SeM genes of 60 S. equi isolates from 27 strangles outbreaks.
  • Through this analysis, they found 21 DNA codon changes that resulted in the nonsynonymous substitution of 18 amino acids, allowing them to categorize the S. equi strains into 15 distinct subtypes. These variations are due to selective immune pressure on certain gene segments – a factor that contributes to the evolution and differentiation of bacterial strains.

Investigation of Live Vaccine-Related Disease Cases

  • As part of the study, the researchers also investigated potential cases of disease related to the administration of a live attenuated S. equi vaccine, known as the Equilis StrepE vaccine.
  • The researchers developed and employed a PCR diagnostic test that identifies a partial gene deletion in the vaccine strain. This enabled them to successfully differentiate the vaccine strain from field strains of S. equi responsible for concurrent disease.
  • The findings showed that while the vaccine strain can be responsible for injection site lesions, it was not the cause of the seven strangles outbreaks investigated in the study among recently vaccinated horses. All outbreaks were due to concurrent infection with wild-type S. equi and not due to reversion of the vaccine strain.

Implications of the Research

  • This research demonstrates the applicability and effectiveness of SeM gene subtyping as a method to identify distinct strains of S. equi and to track the source of disease outbreaks.
  • The ability to differentiate between the vaccine strain and wild strains can counter any mistaken attribution of illness to the vaccine, maintaining confidence in its use and supplying crucial information for future vaccine development.
  • Finally, this detailed understanding of S. equi strains can contribute to improved treatment and prevention strategies for strangles.

Cite This Article

APA
Kelly C, Bugg M, Robinson C, Mitchell Z, Davis-Poynter N, Newton JR, Jolley KA, Maiden MC, Waller AS. (2006). Sequence variation of the SeM gene of Streptococcus equi allows discrimination of the source of strangles outbreaks. J Clin Microbiol, 44(2), 480-486. https://doi.org/10.1128/JCM.44.2.480-486.2006

Publication

Journal of clinical microbiology
ISSN: 0095-1137
NlmUniqueID: 7505564
Country: United States
Language: English
Volume: 44
Issue: 2
Pages: 480-486

Researcher Affiliations

Kelly, Charlotte
  • Centre for Preventive Medicine, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU, United Kingdom.
Bugg, Maxine
    Robinson, Carl
      Mitchell, Zoe
        Davis-Poynter, Nick
          Newton, J Richard
            Jolley, Keith A
              Maiden, Martin C J
                Waller, Andrew S

                  MeSH Terms

                  • Amino Acid Sequence
                  • Animals
                  • Antigens, Bacterial / chemistry
                  • Antigens, Bacterial / genetics
                  • Bacterial Proteins / chemistry
                  • Bacterial Proteins / genetics
                  • Disease Outbreaks
                  • Gene Deletion
                  • Genetic Variation
                  • Horse Diseases / epidemiology
                  • Horse Diseases / microbiology
                  • Horse Diseases / prevention & control
                  • Horses
                  • Molecular Sequence Data
                  • Polymerase Chain Reaction / methods
                  • Streptococcal Infections / epidemiology
                  • Streptococcal Infections / microbiology
                  • Streptococcal Infections / prevention & control
                  • Streptococcal Infections / veterinary
                  • Streptococcal Vaccines / administration & dosage
                  • Streptococcal Vaccines / genetics
                  • Streptococcus equi / classification
                  • Streptococcus equi / genetics
                  • Streptococcus equi / immunology
                  • Streptococcus equi / isolation & purification
                  • Vaccination / veterinary
                  • Vaccines, Attenuated / administration & dosage
                  • Vaccines, Attenuated / genetics

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