Molecular epidemiology of Streptococcus equi subsp. zooepidemicus isolated from horses with respiratory diseases

Streptococcus equi subsp. zooepidemicus (SEZ) is one of the most important bacteria associated with inflammatory airway disease in British young horses (1). SEZ has been isolated also from humans with different kinds of diseases, therefore it is suspected of being a zoonotic agent (2). Some subtyping techniques have been described for molecular epidemiological investigations of SEZ isolated from horses (3, 4, 5). The aim of this study was to investigate the molecular epidemiology of SEZ isolated from horses with a history of respiratory diseases in Italy. A total of 46 SEZ strains identified by multiplex PCR (6) and isolated from nasal swabs, tracheal washes, guttural pouch lavages, bronchoalveolar lavages and lungs of horses with different respiratory signs were typed by a PCR technique based on the 16S-23S rRNA gene intergenic spacer. The PCR typing method was based on four different reactions (3, 4, 5). A single expected PCR product was obtained in 26 out of 46 samples, 16 of which corresponded to type A1. Multiple products were obtained from 20 samples. In particular, two PCR products were obtained from 16 samples, 8 of which gave an unexpected PCR product of about 200 bp, three products were observed in 3 samples and 5 products were present in one sample. The unexpected PCR product was sequenced and named A2a. In all, 16 different SEZ types were isolated. Similarly as reported in British horses, type A1 was the most prevalent intergenic spacer. Furthermore, the new type A2a was found. These results show that SEZ isolated from horses in Italy represent a wide diversity of strain types and confirm that SEZ are heterogeneous bacteria. Further investigation will be carried out in asymptomatic horses. Molecular epidemiological studies of SEZ infecting horses could be useful for selecting candidate strains to be included in experimental vaccines.