Streptococcus suis subsp. hashimotonensis subsp. nov.: Lancefield group A antigen–positive organisms isolated from human clinical specimens and wild boar oral cavity samples

Three Streptococcus suis-like strains positive for Lancefield antigen group A were isolated from human boar bite wounds and the oral cavities of boars in Hashimoto City, Wakayama Prefecture, Japan, and their taxonomic positions were investigated. Application of the VITEK2 system identified all three isolates as S. suis with > 94 % probability. The isolates were assigned to S. suis based on the results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis (Biotyper score of 2.382) but were differentiated according to the characteristic signal peaks (4709 m/z and 9420 m/z) that were not present for S. suis. Sequence analysis of the 16S rRNA and sodA genes determined that the isolates were similar to S. suis; however, these genes appeared on a phylogenetic sub-branch. Phylogenetic analysis of the whole chromosomal DNA showed that the isolate formed a cluster with S. suis but with clear divergence. The average nucleotide index using BLAST between the clinical isolate (PAGU 2482) and a closely related reference strain of S. suis was 94.75 %, which was not clearly conclusive; however, digital DNA-DNA hybridization showed a value of 61.2 %. Biochemical reactions, including those with acid phosphatase, α-chymotrypsin, and tagatose (acidification), distinguished our isolates from S. suis. Thus, based on phylogenetic, genomic, and phenotypic characteristics and MALDI-TOF-MS signal patterns, we propose that the isolate with Lancefield group A positive characteristics be designated as a novel subspecies, Streptococcus suis subsp. hashimotonensis subsp. nov., with the type strain PAGU 2482^T (GTC 18290^T = CCUG 77434^T).