Streptococcus equi subsp. equi

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Characteristics of the symbiont/pathogen

The pathogen involved in this symbionic relationship Streptococcus equi. The bacterium S. equi subsp. equi infects Equus caballus, the horse, and causes a disease called Strangles.

S. equi is a gram positive bacterium. Irregularly shaped cocci are typical of the species. Its incubation period is 3-14 days. The bacterium, which is in Lancefield’s group C, also causes red blood cells to lyse [Sweeney et. al.]. The bacterium can be grown on blood agar at 37°C under aerobic conditions. The bacteria form β-haemolytic colonies, which appear mucousy with no pigment. They are catalase-negative and facultative anaerobes. In a study to determine species of an unknown bacterium, certain strains and other species of the Streptococcus genus were looked at. In this study, Fernandez et. al. looked at S. equi subsp. ruminatorum subsp. nov., but they also looked at general features of the S. equi species including other strains (subsp. equi and subsp. zooepidemicus). The scientists found several characteristics in the different species that distinguish them from each other, and they also found some characteristics unique to S. equi [1]. S. equi subsp. equi is thought to have evolved from S. equi subsp. zooepidemicus, which is usually harmless. Only S. equi subsp. equi actually causes Strangles, though [2].

S. equi produces a protein called SeM, which increases its virulence. The protein binds fibrinogen and immunoglobulin G in order to inhibit the deposition of C3b. This causes phagocytes to be destroyed. The protein contains a sub-typing region (the region in which alterations of amino acid codes are present), a fibrinogen binding region, and an IgG binding region [3].

The genome of S. equi contains 2253793 base pairs and contains circular DNA. The complete genome of the species has been discovered [2].

Characteristics of the host

What host/s is/are involved? Is there host specificity? Are there secondary reservoirs?


Host-Symbiont Interaction

What kind of interaction do host and symbiont have? How is the host affected by the relationship? How does the host acquire and transmit the symbiont? Is the interaction obligate or facultative?

Molecular Insights into the Symbiosis

Describe molecular/genetic studies on the symbiosis.

Ecological and Evolutionary Aspects

What is the evolutionary history of the interaction? Do particular environmental factors play a role in regulating the symbiosis?

Recent Discoveries

Describe two findings on the symbiosis published within the last two years.

References

[1] Fernandez, E., Blume, V., Garrido, P., Collins, M.D., Mateos, A., Dominquez, L., and Fernandez-Garayzabal, J.F. 2004 Streptococcus equi subsp. ruminatorum subsp. nov., isolated from mastitis in small ruminants. International Journal of Systematic and Evolutionary Microbioogy 54:2291-2296.

[2] Holden, M.T.G., Heather, Z., Paillot, R., Steward, K.F., Webb, K., Ainslie, F., Jourdan, T., Bason, N.C., Holroyd, N.E., Mungall, Kl, Quail, M.A., Sanders, M., Simmonds, M., Willey, D., Brooks, K., Aanensen, D.M., Spratt, B.G., Jolley, K.A., Maiden, M.C.J., Kehoe, M., Chanter, N., Bentley, S.D., Robinson, C., Maskell, D.J., Parkhill, J., and Waller, A.S. 2009. Genomic evidence for the evolution of Streptococcus equi: host restriction, increased virulence, and genetic exchange with human pathogens. PLoS Pathogens 5:1-14.

[3] Kelly, C., Bugg, M., Robinson, C., Mitchell, Z., Davis-Poynter, N., Newton, R., Jolley, K.A., Maiden, M.C.J., and Waller, A.S. 2006. Sequence variation of the SeM Gene of Streptococcus equi allows discrimination of the source of strangles outbreaks. Journal of Clinical Microbiology 44:480-486.

Sweeney, C.R., Timoney, J.F., Newton, J.R., Hines, M.T. 2005. Streptococcus equi infections in horses: Guidelines for treatment, control, and prevention of strangles. J Vet Intern Med 19:123-134.

[Sample reference] [[1] Seemanapalli SV, Xu Q, McShan K, Liang FT. 2010. Outer surface protein C is a dissemination-facilitating factor of Borrelia burgdorferi during mammalian infection. PLoS One 5:e15830.]

Edited by Brooke Reamer, students of Grace Lim-Fong