Streptococcus azizii sp. nov., isolated from naïve weanling mice

Abstract

Three isolates of a previously reported novel catalase-negative, Gram-stain-positive, coccoid, alpha-haemolytic, Streptococcus species that were associated with meningoencephalitis in naïve weanling mice were further evaluated to confirm their taxonomic status and to determine additional phenotypic and molecular characteristics. Comparative 16S rRNA gene sequence analysis showed nearly identical intra-species sequence similarity (≥99.9 %), and revealed the closest phylogenetically related species, Streptococcus acidominimus and Streptococcuscuniculi, with 97.0 and 97.5 % sequence similarity, respectively. The rpoB, sodA and recN genes were identical for the three isolates and were 87.6, 85.7 and 82.5 % similar to S. acidominimus and 89.7, 86.2 and 80.7 % similar to S. cuniculi, respectively. In silico DNA-DNA hybridization analyses of mouse isolate 12-5202^T against S. acidominimus CCUG 27296^T and S. cuniculi CCUG 65085^T produced estimated values of 26.4 and 25.7 % relatedness, and the calculated average nucleotide identity values were 81.9 and 81.7, respectively. These data confirm the taxonomic status of 12-5202^T as a distinct Streptococcus species, and we formally propose the type strain, Streptococcusazizii 12-5202^T (=CCUG 69378^T=DSM 103678^T). The genome of Streptococcus azizii sp. nov. 12-5202^T contains 2062 total genes with a size of 2.34 Mbp, and an average G+C content of 42.76 mol%.

Keywords: Streptococcus; firmicutes; mice; taxonomy.

Fig. 1.

Maximum-likelihood phylogenetic tree inferred from 16S rRNA gene sequences from select streptococci. The phylogenetic position of strain 12-5202^T from the brain tissue of a 29-day-old male mouse is shown in bold text in relationship with other species of the Streptococcus genus. Enterococcus faecalis was used as the outgroup. GenBank accession numbers for gene and locus tags for whole genome sequences are in parentheses. Bootstrap values ≥70 % are shown. Bar, 0.05 substitutions per site.