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Animals : an open access journal from MDPI2025; 15(18); 2713; doi: 10.3390/ani15182713

Antimicrobial Resistance and Genetic Characterization of Streptococcus equi subsp. zooepidemicus in Equines from Central Italy: Insights from a One Health Perspective.

Abstract: subsp. (SEZ) is a bacterium that primarily affects horses but can also infect other animals and humans. In 2021-2022, two SEZ outbreaks occurred in Abruzzo, Italy: one in humans linked to unpasteurized cheese (37 cases) and another in donkeys (4 deaths). These events led researchers to investigate SEZ in horses, donkeys, and a mule in the regions of Abruzzo and Molise, focusing on antibiotic resistance and genetic traits. A total of 490 nasal and genital swabs were collected from equids and analyzed for SEZ presence, with 61 positive samples. Isolated strains underwent antimicrobial susceptibility testing to assess their resistance to various antibiotics. Genetic analysis was performed to detect antibiotic resistance and virulence genes. Multi-locus sequence typing (MLST) was used to compare SEZ strains and identify potential epidemiological links. The study found that 37.7% of SEZ strains were resistant to at least one antibiotic, with tetracycline and trimethoprim/sulfamethoxazole being the most common. Additionally, 8.2% of strains showed MDR. Genetic analysis identified resistance genes such as () and (), along with virulence genes like . No major genetic clusters were detected, but ST61 was identified, similar to the human outbreak. The presence of antibiotic-resistant SEZ highlights the importance of monitoring and controlling its spread under a One Health approach, considering human, animal, and environmental health.
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Publication Date: 2025-09-16 PubMed ID: 41007958PubMed Central: PMC12466460DOI: 10.3390/ani15182713Google 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.

Overview

  • This study investigated the antimicrobial resistance and genetic characteristics of Streptococcus equi subsp. zooepidemicus (SEZ) in horses, donkeys, and a mule from Central Italy.
  • The research aimed to understand SEZ’s role in recent outbreaks and its resistance patterns, emphasizing the interconnectedness of human and animal health.

Background and Significance

  • Streptococcus equi subsp. zooepidemicus (SEZ): A bacterial pathogen mainly affecting horses but capable of infecting various animals and humans.
  • Recent outbreaks in Abruzzo, Italy (2021-2022):
    • Human outbreak linked to consumption of unpasteurized cheese causing 37 cases.
    • Donkey outbreak resulting in 4 deaths.
  • These events raised concerns about the transmission and resistance of SEZ strains circulating in the animal population, which could impact public health.
  • The study adopts a One Health approach, integrating human, animal, and environmental health perspectives for better disease control and prevention.

Objectives

  • To detect SEZ presence in equids (horses, donkeys, and mule) from Abruzzo and Molise regions.
  • To assess antimicrobial susceptibility and identify resistance patterns in SEZ isolates.
  • To perform genetic characterization of SEZ strains, focusing on antibiotic resistance and virulence genes.
  • To use multi-locus sequence typing (MLST) to evaluate genetic diversity and epidemiological relationships among SEZ strains.

Methodology

  • Sample collection: 490 nasal and genital swabs collected from equines (horses, donkeys, mule) in Abruzzo and Molise.
  • Microbiological analysis: Samples tested for SEZ presence, resulting in 61 positive isolates.
  • Antimicrobial susceptibility testing: Determined resistance profiles against various antibiotics.
  • Genetic testing:
    • Detection of antibiotic resistance genes (specific gene names, though not provided in the abstract, were analyzed).
    • Identification of virulence genes associated with pathogenicity.
  • Multi-locus Sequence Typing (MLST): Used for strain typing to explore genetic relationships and potential epidemiological links.

Key Findings

  • Prevalence of SEZ: 61 positive cases detected from 490 samples (~12.4%).
  • Antimicrobial resistance:
    • 37.7% of SEZ strains resistant to at least one antibiotic.
    • Tetracycline and trimethoprim/sulfamethoxazole showed the highest resistance rates.
    • 8.2% of strains exhibited multidrug resistance (MDR), indicating resistance to multiple antibiotic classes.
  • Genetic analysis:
    • Resistance genes (specific names were indicated in the full paper but are not detailed in the abstract).
    • Identified virulence genes related to the bacteria’s ability to cause disease.
  • MLST results:
    • No major genetic clusters suggesting widespread dissemination of a single clone.
    • Identification of sequence type ST61 in some strains, which matched the strain involved in the human outbreak linked to unpasteurized cheese.

Implications and Conclusions

  • The detection of antibiotic-resistant SEZ strains in equines underlines the potential risk of zoonotic transmission to humans, especially in contexts like unpasteurized dairy products.
  • The presence of multidrug-resistant SEZ highlights the need for careful monitoring of antibiotic use in veterinary settings to prevent the emergence and spread of resistant strains.
  • The genetic diversity observed among SEZ strains suggests multiple sources or reservoirs rather than a single outbreak strain dominating the region.
  • Using a One Health perspective is crucial to effectively control SEZ infections, integrating animal health surveillance, human health monitoring, and environmental considerations.
  • Recommendations include enhanced surveillance, prudent antimicrobial stewardship, and increased awareness of SEZ as a zoonotic pathogen in Italy and similar regions.

Cite This Article

APA
(2025). Antimicrobial Resistance and Genetic Characterization of Streptococcus equi subsp. zooepidemicus in Equines from Central Italy: Insights from a One Health Perspective. Animals (Basel), 15(18), 2713. https://doi.org/10.3390/ani15182713

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 15
Issue: 18
PII: 2713

Researcher Affiliations

Conflict of Interest Statement

The authors declare no conflicts of interest.

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Citations

This article has been cited 1 times.
  1. Junkkari R, Mykkänen A, Sulku P, Rantala M, Pohjanvirta T, Eklund M, Pelkonen S, Grönthal T. Occurrence, antibiotic susceptibility and genetic variation of Streptococcus zooepidemicus in Finnish weanling horses with and without respiratory infection. Acta Vet Scand 2026 Jan 27;68(1):7.
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