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

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.