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Antimicrobial Resistance and Genetic Characterization of Streptococcus equi subsp. zooepidemicus in Equines from Central Italy: Insights from a One Health Perspective
by
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Alessandra Alessiani
1,*,
Marina Baffoni
1,*,
Daniela Averaimo
1,
Maria Chiara Cantelmi
1,
Antonio Coccaro
1,
Marco Rulli
1,
Vanessa Piersanti
1,2,
Cinzia Pompilii
1,
Francesca Cito
1,
Alexandra Chiaverini
1 and
Antonio Petrini
1 1
Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise “G. Caporale”, 64100 Teramo, Italy
2
Dipartimento di Medicina Clinica, Sanità Pubblica, Scienze della Vita e dell’Ambiente, Università degli Studi Dell’Aquila, 67100 L’Aquila, Italy
*
Authors to whom correspondence should be addressed.
Animals 2025, 15(18), 2713; https://doi.org/10.3390/ani15182713
Submission received: 4 August 2025
/
Revised: 12 September 2025
/
Accepted: 15 September 2025
/
Published: 16 September 2025
(This article belongs to the Section Veterinary Clinical Studies)
Simple Summary
Streptococcus equi subsp. zooepidemicus (SEZ) is a bacterium commonly found in horses but can also infect other animals and humans. In 2021–2022, Abruzzo experienced two SEZ outbreaks: one in humans linked to unpasteurized cheese (37 cases) and another in donkeys (4 deaths). This led researchers to study SEZ in horses, donkeys, and a mule in Abruzzo and Molise. Sixty-one nasal and genital swabs were tested for antibiotic resistance and genetic traits. Results showed that 37.7% of SEZ strains were resistant to at least one antibiotic, with tetracycline and trimethoprim/sulfamethoxazole being the most common. About 8.2% of strains were multidrug-resistant (MDR). Genetic testing identified resistance genes like tet(W) and erm(B), and virulence genes like Fbp54 (which helps SEZ attach to host tissues). This study found no major clusters of related SEZ strains but detected ST61, linked to the human outbreak. The presence of antibiotic-resistant SEZ, including strains with multiple resistance genes, underscores the importance of meticulous monitoring to prevent the spread of resistant bacteria, particularly under a One Health approach that considers human, animal, and environmental health in tandem.
Abstract
Streptococcus equi subsp. zooepidemicus (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 tet(W) and erm(B), along with virulence genes like Fbp54. 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.
