Reappraisal of the taxonomy of Streptococcus suis serotypes 20, 22 and 26: Streptococcus parasuis sp. nov.

Abstract

In order to clarify the taxonomic position of serotypes 20, 22 and 26 of Streptococcus suis, biochemical and molecular genetic studies were performed on isolates (SUT-7, SUT-286 T , SUT-319, SUT-328 and SUT-380) reacted with specific antisera of serotypes 20, 22 or 26 from the saliva of healthy pigs as well as reference strains of serotypes 20, 22 and 26. Comparative recN gene sequencing showed high genetic relatedness among our isolates, but marked differences from the type strain S. suis NCTC 10234 T , i.e. 74.8-75.7 % sequence similarity. The genomic relatedness between the isolates and other strains of species of the genus Streptococcus, including S. suis, was calculated using the average nucleotide identity values of whole genome sequences, which indicated that serotypes 20, 22 and 26 should be removed taxonomically from S. suis and treated as a novel genomic species. Comparative sequence analysis revealed 99.0-100 % sequence similarities for the 16S rRNA genes between the reference strains of serotypes 20, 22 and 26, and our isolates. Isolate STU-286 T had relatively high 16S rRNA gene sequence similarity with S. suis NCTC 10234 T (98.8 %). SUT-286 T could be distinguished from S. suis and other closely related species of the genus Streptococcus using biochemical tests. Due to its phylogenetic and phenotypic similarities to S. suis we propose naming the novel species Streptococcus parasuis sp. nov., with SUT-286 T (5JCM 30273 T 5DSM 29126 T ) as the type strain.Streptococcus suis is a major pathogen of swine and has also been isolated from a variety of animals such as ruminants, cats, dogs, deer and horses (Staats et al., 1997). Moreover, human S. suis infection is considered to be one of the most important emerging zoonotic diseases in Asian countries (Gottschalk et al., 2010). On the basis of their polysaccharide capsular antigens, a total of 33 serotypes (types 1-31, 33 and type 1/2) of S. suis have been described elsewhere (Gottschalk et al., 1989(Gottschalk et al., , 1991Higgins et al., 1995), in which serotype 2 was most frequently associated with disease in both pigs and humans (Gottschalk et al., 2007). Genetic relatedness among S. suis serotypes has been described previously by several investigators. However, a phylogenetic analysis based on 16S rRNA gene and chaperonin-60 gene sequences comparison (Chatellier et al., 1998; Brousseau et al., 2001) indicated a marked genetic discrepancy between serotypes 20, 22, 26 and 33 and other serotypes of S. suis. Moreover, our previous study (Tien et al. 2013) suggested that the reference strains of serotypes 20, 22, 26 and 33 should be removed taxonomically from S. suis. This was based on DNA-DNA relatedness 3Present address:

Simultaneous detection of 33 Streptococcus suis serotypes using the luminex xTAG® assay™

“…The Streptococcus orisratti strains originally classified as the reference strains for S. suis serotypes 32 (strain EA1172.91) and 34 (strain 92-2742) were not included in the present study (Hill et al, 2005). Although additional serotypes 20, 22 and 26 have recently been suggested to belong to a bacterial species different from S. suis (Nomoto et al, 2015;Tien le et al, 2013), these serotypes are still commonly isolated from diseased animals and considered as S. suis by diagnostic laboratories . For that reason, they have been included in the development of the present test.…”

Development of loop-mediated isothermal amplification to detect Streptococcus suis and its application to retail pork meat in Japan

“…However, phylogenetic analyses of the 16S rRNA and chaperonin-60 (cpn60) genes showed that the reference strains of serotypes 32 and 34 should have been Streptococcus orisratti (Hill et al, 2005). More recent sequence analyses of genes encoding manganese-dependent superoxide dismutase (sodA) and the recombination/repair protein (recN) indicated that the reference strains of serotypes 20, 22, 26, and 33 need to be taxonomically removed from S. suis (Tien le et al, 2013), and serotypes 20, 22, and 26 was reappraised and proposed to be a novel species, Streptococcus parasuis (Nomoto et al, 2015). Notomi et al (2000) developed a nucleic acid amplification method called loop-mediated isothermal amplification (LAMP), the reaction which is performed under isothermal conditions with a set of four to six specially designed primers and can be accomplished in a single step without the need for advanced instruments (Mori and Notomi, …”

Identification of six novel capsular polysaccharide loci ( NCL ) from Streptococcus suis multidrug resistant non‐typeable strains and the pathogenic characteristic of strains carrying new NCL s

“…Later, S. suis serotypes 20, 22 and 26 were proposed to be Streptococcus parasuis sp. nov. (Nomoto et al, 2015), and S. suis serotype 33 was proposed to be Streptococcus ruminantium sp. nov. (Tohya et al, 2017).…”