Population structure, genetic diversity and pathotypes ofStreptococcus suisisolated during the last 13 years from diseased pigs in Switzerland

Streptococcus(S.)suisis a globally important swine pathogen, which comprises certain zoonotic serotypes. In this study, a detailed characterization of 88 porcineS. suisisolates was performed by analyzing capsular (cps) types, multilocus sequence typing (MLST) and investigation of the minimum core genome (MCG). In order to focus on the virulence potential of presumable invasive disease-associatedS. suisisolates, virulence-associated gene profiles were assessed followed by screening a chosen subset ofS. suisstrains with a molecular pathotyping tool. Results showed a high genetic variability within this strain collection. In total, seventeencpstypes were identified with a predominance ofcpstype 9 (15.9%) and 6 (14.8%). MLST revealed 48 sequence types (STs) including 41 novel ones. The population structure ofS. suiswas heterogenous and isolates belonged to eight different clonal complexes (CCs) including CC28 (9.1%), CC1109 (8%), CC13/149 (6.8%), CC1237 (5.7%), CC1 (3.4%), CC17 (3.4%), CC87 (2.3%), and CC1112 (1.1%), whereas a significant portion of isolates (60.2%) could not be assigned to any described CCs. Virulence-associated markers, namely extracellular protein factor (epf), muramidase-released protein (mrp), and suilysin (sly), showed a link with STs rather than withcpstypes. With this study an expanded knowledge about the population structure and the genetic diversity ofS. suiscould be achieved, which helps to contribute to an optimal public health surveillance system by promoting a focus on strains with an increased virulence and zoonotic potential.