FIRST CHARACTERIZATION OF STREPTOCOCCUS EQUI SUBSP. ZOOEPIDEMICUS SEQUENCE TYPE 525 IN DONKEYS OF ABRUZZO REGION, ITALY

Streptococcus equi subsp. zooepidemicus (SEZ) is a Lancefield group C β-haemolytic Streptococcus that is usually considered a commensal bacterium of the oral cavity, pharynx, and respiratory tract of horses (1). In the present case study series, we described the diagnostic process applied to characterize the streptococcal infection caused by a novel SEZ sequence type (ST525) in donkeys located on a farm in Abruzzi, Italy. A total of 4 donkeys died between March and April 2022 after showing respiratory signs. The diagnostic process began with history taking and with anatomopathological investigations which showed hemorrhagic pneumonia and septicemia. Then, SEZ infection was confirmed by applying an innovative diagnostic strategy that put together standard bacterial isolation techniques, analytical tools for bacteria identification (MALDI-TOF MS), and molecular techniques (qPCR). Furthermore, the application of the DNA sequencing approach helps us to characterize the bacterial strains and the virulence factors involved in animal diseases. The novel SEZ-ST525 was identified in all the cases of the disease. This new sequence type was isolated from the lung, liver, and spleen in Case 1, and from retropharyngeal lymph nodes in Case 2. Moreover, the presence of the virulence gene mf2, a virulence factor carried by prophages in Streptococcus pyogenes, was also found for the first time in an SEZ strain. Our results demonstrated the need to apply new diagnostic tools, such as genomic sequencing technologies, for the identification and tracking of pathogenic strains of SEZ, shedding new light on the revaluation of this bacteria as a causative agent of disease in animals and humans.