Streptococcus spp. in Equines - Infection and Antimicrobial Susceptibility Profiles


  • Mariana Costa Torres Departamento de Patologia Clínica Veterinária, Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS)
  • Camila Azevedo Moni Departamento de Patologia Clínica Veterinária, Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS)
  • Luiza de Campos Menetrier Departamento de Patologia Clínica Veterinária, Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS)
  • Gabriela Merker Breyer Departamento de Patologia Clínica Veterinária, Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS)
  • Franciele Maboni Siqueira Departamento de Patologia Clínica Veterinária, Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS)



Background: Empirical antimicrobial prescribing is commonly used in equine veterinary. Therefore, professionals can obtain information about antimicrobial susceptibility profile of the bacterial strains based on veterinary literature. Considering equine infections, Streptococcus spp. are important pathogens that can cause serious damage in horses. Therefore, the aim of this study was to describe the antimicrobial susceptibility testing (AST) and infection profiles of Streptococcus spp. strains isolated from equines with infectious diseases subjected to microbiological analysis.  

Materials, Methods & Results: Veterinarians sent 13 samples and culture in Blood and MacConkey Agar were performed. After the incubation period, suspected colonies, which showed significative growth, were analyzed by Gram-staining, biochemical tests, and subjected to confirmatory identification in Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry. In vitro AST analysis were performed by disc diffusion method, in accordance with the veterinarians' request. The antimicrobials tested in this study were: ceftiofur, gentamicin, ampicillin, enrofloxacin, amikacin, penicillin, trimethoprim-sulfamethoxazole, ciprofloxacin, doxycycline, vancomycin and metronidazole. The samples included uterine exudate, hock fistula, osteosynthesis exudate, exudate from the guttural pouch, and were originated from animals located in different and distant geographical regions in the cities of Porto Alegre, Pelotas, and Bagé, Rio Grande do Sul, Brazil. Streptococcus dysgalactiae, Streptococcus equi and Streptococcus thoraltensis were the Streptococcus species identified in the samples. S. dysgalactiae was the mainly species found in the uterus samples, while S. thoraltensis, an unusual Streptococcus species, was identified as etiological agent of endometritis in 2 of the analyzed animals. On the other hand, S. equi was found in both the guttural pouch, representing the etiological agent of the strangle case, and in the osteosynthesis exudate, as infectious agent of post-osteosynthesis surgery. The majority of streptococci strains were susceptible to ceftiofur drug. Amikacin and ciprofloxacin, however, were the drugs for which the strains were mainly resistant according to the results.

Discussion: The present study provided the AST and infection profile of Streptococcus species related to equine infectious diseases. S. dysgalactiae is considered an unusual bacterium isolated from horses that can be related to endometritis, S. equi is the causative agent of strangles, and S. thoraltensis is unusual in equines. Generally, the observed susceptibility to ceftiofur of the strains analyzed was in agreement with previous results reported in the literature. However, ceftiofur is a third-generation cephalosporin and is considered a critically important antibiotic for human health and its use in veterinary medicine should be cautious. Considering the resistance profile found, Streptococcus spp. can be intrinsically resistant to low drug concentrations of aminoglycosides. Moreover, the emergence and spread of fluoroquinolones resistance may also be due to the acquisition of resistance via horizontal gene transfer. Therefore, the present study described both infection and antimicrobial susceptibility patterns of Streptococcus strains related to equine infectious diseases. Considering the findings, the results found in this study might contribute to the decision-making by veterinarians to further equine treatments.

Keywords: antimicrobial susceptibility, pattern, AST, drug, resistant bacteria, horses, veterinarians.


Download data is not yet available.


Bianchi M.V., Mello L.S., Ribeiro P.R., Wentz M.F., Stolf A.S., Lopes B.C., Andrade C.P., Snel G.G.M., Sonne L., Driemeier D. & Pavarini S.P. 2020. Causes and pathology of equine pneumonia and pleuritis in southern Brazil. Journal of Comparative Pathology. 179: 65-73. DOI: 10.1016/j.jcpa.2020.07.006

Bowen M. 2013. Antimicrobial stewardship: time for change. Equine Veterinary Journal. 45: 127-129. DOI: 10.1111/evj.12041

Brazilian Committee on Antimicrobial Susceptibility Testing (BrCAST). 2022. Tabelas de Pontos de Corte para Interpretação de CIMs e Diâmetros de Halos. v.12.0. Rio de Janeiro: BrCAST, 88p.

Cattoir V. 2016. Mechanisms of Antibiotic Resistance. In: Ferretti J.J., Stevens D.L. & Fischetti V.A. (Eds). Streptococcus pyogenes: Basic Biology to Clinical Manifestations. Oklahoma City: University of Oklahoma Health Sciences Center, pp.947-992.

Clinical and Laboratory Standards Institute (CLSI). 2015. Performance Standards for Antimicrobial Susceptibility Testing; Twenty-Fifth Informational Supplement. Wayne, PA. CLSI document M100-S25. Wayne: CLSI, 240p.

Clinical and Laboratory Standards Institute (CLSI). 2018. Performance Standards for Antimicrobial Disk and Dilution Susceptibility Tests for Bacteria Isolated from Animals. Wayne, PA. CLSI standard VET01. Wayne: CLSI, 156p.

Espíndola J.P., Machado G., Diehl G.N., Santos L.C., Vargas A.C. & Gressler L.T. 2022. Culturable microbial population from the upper respiratory tract of 1,010 clinically healthy horses in southern Brazil. Journal of Equine Veterinary Science. 114: 1-4. DOI: 10.1016/j.jevs.2022.103946

Hughes L.A., Pinchbeck G., Callaby R., Dawson S., Clegg P. & Williams N. 2013. Antimicrobial prescribing practice in UK equine veterinary practice. Equine Veterinary Journal. 45: 141-147. DOI: 10.1111/j.2042-3306.2012.00602.x

Ikhuoso O.A., Monroy J.C., Rivas-Caceres R.R., Cipriano-Salazar M. & Pliego A.B. 2020. Streptococcus equi in equine: diagnostic and healthy performance impacts. Journal of Equine Veterinary Science. 85: 1-4. DOI: 10.1016/j.jevs.2019.102870

Janda W.M. 2014. The genus Streptococcus – Part I: Emerging pathogens in the “Pyogenic Cocci” and the “Streptococcus bovis” groups. Clinical Microbiology. 36(20): 157-166. DOI: 10.1016/j.clinmicnews.2014.10.001

Jaramillo-Morales C., Gomez D.E., Renaud D. & Arroyo L.G. 2022. Streptococcus equi culture prevalence, associated risk factors and antimicrobial susceptibility in a horse population from Colombia. Journal of Equine Veterinary Science. 111: 1-6. DOI: 10.1016/j.jevs.2022.103890

Johns I.C. & Adams E.L. 2015. Trends in antimicrobial resistance in equine bacterial isolates: 1999–2012. The Veterinary Record. 176(13): 334-340. DOI: 10.1136/vr.102708

Ko W.C. & Hsueh P.R. 2009. Increasing extended-spectrum b-lactamase production and quinolone resistance among gram-negative bacilli causing intra-abdominal infections in the Asia/Pacific region: data from the smart study 2002-2006. Journal of Infection. 59: 95-103. DOI: 10.1016/j.jinf.2009.06.003

Li J., Zhao Y., Gao Y., Zhu Y., Holyoak G.R. & Zeng S. 2021. Treatments for endometritis in mares caused by Streptococcus equi subspecies zooepidemicus: a structured literature review. Journal of Equine Veterinary Science. 102: 1-10. DOI: 10.1016/j.jevs.2021.103430

Moreno L.Z., Matajira C.E.C., Gomes V.T.M., Silva A.P.S., Mesquita R.E., Christ A.P.G., Sato M.I. & Moreno A.M. 2016. Molecular and antimicrobial susceptibility profiling of atypical Streptococcus species from porcine clinical specimens. Infection, Genetics and Evolution. 44: 376-381. DOI: 10.1016/j.meegid.2016.07.045

Pinho M.D., Melo-Cristino J. & Ramirez M. 2010. Fluoroquinolone resistance in Streptococcus dysgalactiae subsp. equisimilis and evidence for a shared global gene pool with Streptococcus pyogenes. Antimicrobial Agents and Chemotherapy. 54(5): 1769-1777. DOI: 10.1128/AAC.01377-09

Proietti P.C., Bietta A., Coppola G., Felicetti M., Cook R.F., Coletti M., Marenzoni M.L. & Passamonti F. 2011. Isolation and characterization of b-haemolytic-streptococci from endometritis in mares. Veterinary Microbiology. 152: 126-130. DOI: 10.1016/j.vetmic.2011.04.009

Stewart G.C. 2013. Streptococcus and Enterococcus. In: McVey S.D., Kennedy M. & Chengappa M.M. (Eds). Veterinary Microbiology. 3rd edn. Rio de Janeiro: Guanabara Koogan, pp.194-202.

Timoney J.F. 2004. The pathogenic equine streptococci. Veterinary Research. 35(4): 397-409. DOI: 10.1051/vetres:2004025

World Health Organization. 2018. Critically Important Antimicrobials for Human Medicine. 6th edn. Geneva: World Health Organization, 52p.

Additional Files



How to Cite

Costa Torres, M., Azevedo Moni, C. ., de Campos Menetrier, L., Merker Breyer, G. ., & Maboni Siqueira, F. (2022). Streptococcus spp. in Equines - Infection and Antimicrobial Susceptibility Profiles. Acta Scientiae Veterinariae, 50.




Most read articles by the same author(s)