Abstract
Streptococcus suis is one of the most important bacterial pathogens in the porcine industry and also a zoonotic agent. Serotype 9 is becoming one of the most prevalent serotypes within the S. suis population in certain European countries. In the present study, serotype 9 strains isolated from a country where infection due to this serotype is endemic (Spain), were compared to those recovered from Canada, where this serotype is rarely isolated from diseased pigs. For comparison purposes, strains from Brazil and the only strain isolated from a human case, in Thailand, were also incorporated. Firstly, sequence types (STs) were obtained followed by detection of putative virulence factors. Phylogenetic trees were constructed using the non-recombinant single nucleotide polymorphisms from core genomes of tested strains. Most Spanish strains were either ST123 or ST125, whereas Canadian strains were highly heterogeneous. However, the distribution of putative virulence factors was similar in both groups of strains. The fact that ST16 strains harbored more putative virulence genes and shared greater similarity with the genome of human serotype 2 strains suggests that they present a higher zoonotic and virulence potential than those from Canada and Spain. More than 80% of the strains included in this study carried genes associated with resistance to tetracycline, lincosamides and macrolides. Serotype 9 strains may be nearly 400 years old and have evolved in parallel into 2 lineages. The rapid population expansion of dominant lineage 1 occurred within the last 40 years probably due to the rapid development of the porcine industry.
Highlights
Streptococcus suis is one of the most important pathogens in the porcine industry causing septicemia with sudden death, meningitis, and a variety of other diseases [1]
Strains from Spain were chosen since this serotype is the one most frequently isolated from diseased pigs [6]; strains of Canada were included since this serotype is not frequently isolated from diseased pigs [12], whereas those of Brazil were included as controls of strains coming from a completely different environment
Based on multilocus sequence typing (MLST), most Spanish strains included in the present study were either ST123 or ST125, confirming previous reports [37, 45] and clearly showing that these strains are different from those isolated long ago in Spain and in other European countries, which were described to belong to the CC87/CC16 [7, 30, 46]
Summary
Streptococcus suis is one of the most important pathogens in the porcine industry causing septicemia with sudden death, meningitis, and a variety of other diseases [1]. Serotype 9 has become an important and prevalent serotype causing invasive disease in pigs in many European countries [6, 7]. This serotype has been frequently isolated from diseased animals in intensively-reared commercial pig breeds, in Spain, Germany, and the Netherlands [6]. It has been isolated from Iberian pigs reared outdoors, wild boars, and even wild rabbits in Spain [8,9,10]. A human case due to S. suis serotype 9 was recently reported in Thailand [13]
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