Genome specialization and decay of the strangles pathogen, Streptococcus equi, is driven by persistent infection.
Abstract: Strangles, the most frequently diagnosed infectious disease of horses worldwide, is caused by Streptococcus equi. Despite its prevalence, the global diversity and mechanisms underlying the evolution of S. equi as a host-restricted pathogen remain poorly understood. Here, we define the global population structure of this important pathogen and reveal a population replacement in the late 19th or early 20th Century. Our data reveal a dynamic genome that continues to mutate and decay, but also to amplify and acquire genes despite the organism having lost its natural competence and become host-restricted. The lifestyle of S. equi within the horse is defined by short-term acute disease, strangles, followed by long-term infection. Population analysis reveals evidence of convergent evolution in isolates from post-acute disease samples as a result of niche adaptation to persistent infection within a host. Mutations that lead to metabolic streamlining and the loss of virulence determinants are more frequently found in persistent isolates, suggesting that the pathogenic potential of S. equi reduces as a consequence of long-term residency within the horse post-acute disease. An example of this is the deletion of the equibactin siderophore locus that is associated with iron acquisition, which occurs exclusively in persistent isolates, and renders S. equi significantly less able to cause acute disease in the natural host. We identify several loci that may similarly be required for the full virulence of S. equi, directing future research toward the development of new vaccines against this host-restricted pathogen.
© 2015 Harris et al.; Published by Cold Spring Harbor Laboratory Press.
Publication Date: 2015-07-09 PubMed ID: 26160165PubMed Central: PMC4561494DOI: 10.1101/gr.189803.115Google Scholar: Lookup
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Summary
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This research studies the global diversity and evolution of Streptococcus equi, the bacterium causing the most common infectious equine disease called strangles. The study reveals the bacterium continuously mutating and decaying, but still able to acquire and amplify genes. The research also highlights that as S. equi resides long-term within its horse host post-acute disease, its virulence reduces. Findings direct future study towards developing new vaccines against this pathogen.
Understanding the Global Population Structure of Streptococcus equi
- The study aims to understand the global diversity and evolution process of the bacteria Streptococcus equi, which is the main cause of strangles, a common infectious disease in horses.
- Through population analysis, researchers discerned a population shift in the late 19th or early 20th century. This pathogen has a dynamic genome that continues to mutate and decay. Despite losing its natural competence and becoming host-restricted, it still manages to acquire and amplify genes.
Niche Adaptation to Persistent Infection within a Host
- The lifestyle of S. equi within the horse host is characterized by acute strangles disease, followed by a long-term infection. The researchers found evidence of convergent evolution in isolates culled from post-acute disease samples, indicating some form of adaptation to its host over an extended period of infection.
- This adaptation often results in metabolic streamlining and a decrease in the bacterium’s virulence over time. Mutations that lead to these changes are found more frequently in persistent isolates, implying that the pathogenic potential of S. equi lessens as a result of long-term residency within the horse after the acute disease phase.
The Reduction of S. equi Virulence
- In the course of long-term residency within the horse, S. equi loses some of its ability to cause acute disease. A significant example is the deletion of the equibactin siderophore locus, which is integral for iron acquisition.
- This deletion, which exclusively occurs in persistent isolates, greatly reduces the bacterium’s ability to cause acute illness in the horse, suggesting the reduction of S. equi’s virulence over time.
Directions for Future Research
- The research identified several loci that may be required for S. equi’s full virulence. This points to directions for future research focusing on these loci, with the aim of developing new vaccines to counter the disease caused by this host-restricted pathogen.
Cite This Article
APA
Harris SR, Robinson C, Steward KF, Webb KS, Paillot R, Parkhill J, Holden MT, Waller AS.
(2015).
Genome specialization and decay of the strangles pathogen, Streptococcus equi, is driven by persistent infection.
Genome Res, 25(9), 1360-1371.
https://doi.org/10.1101/gr.189803.115 Publication
Researcher Affiliations
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, United Kingdom;
- The Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom;
- The Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom;
- The Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom;
- The Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom;
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, United Kingdom;
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, United Kingdom; School of Medicine, University of St Andrews, North Haugh, St. Andrews KY16 9TF, United Kingdom.
- The Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom;
MeSH Terms
- Animals
- Disease Outbreaks
- Gene Amplification
- Gene Deletion
- Gene Order
- Genetic Loci
- Genome, Bacterial
- Genomics / methods
- Horse Diseases / epidemiology
- Horse Diseases / microbiology
- Horses
- Host-Pathogen Interactions
- Mutagenesis, Insertional
- Phylogeny
- Polymorphism, Single Nucleotide
- Streptococcal Infections / veterinary
- Streptococcus equi / classification
- Streptococcus equi / genetics
- United Kingdom / epidemiology
Grant Funding
- Wellcome Trust
- 098051 / Wellcome Trust
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