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

Kelly, Charlotte, Bugg, Maxine, Robinson, Carl, Mitchell, Zoe, Davis-Poynter, Nick, Newton, J. Richard, Jolley, Keith A., Maiden, Martin C. J. and Waller, Andrew S. (2006) Sequence variation of the SeM gene of Streptococcus equi allows discrimination of the source of strangles outbreaks. Journal of Clinical Microbiology, 44 2: 480-486. doi:10.1128/JCM.44.2.480-486.2006

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Author Kelly, Charlotte
Bugg, Maxine
Robinson, Carl
Mitchell, Zoe
Davis-Poynter, Nick
Newton, J. Richard
Jolley, Keith A.
Maiden, Martin C. J.
Waller, Andrew S.
Title Sequence variation of the SeM gene of Streptococcus equi allows discrimination of the source of strangles outbreaks
Journal name Journal of Clinical Microbiology   Check publisher's open access policy
ISSN 0095-1137
Publication date 2006-02
Sub-type Article (original research)
DOI 10.1128/JCM.44.2.480-486.2006
Open Access Status File (Publisher version)
Volume 44
Issue 2
Start page 480
End page 486
Total pages 7
Place of publication Washington, DC, United States
Publisher American Society for Microbiology
Language eng
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 (non synonymous-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.
Keyword Microbiology
Binding protein Fgbp
Subsp Equi
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
Clinical Medical Virology Centre Publications
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Citation counts: TR Web of Science Citation Count  Cited 47 times in Thomson Reuters Web of Science Article | Citations
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Created: Fri, 25 Jan 2008, 16:46:01 EST