Streptococcus atopica sp. nov., Isolated from the Feces of a Toddler with Atopic Dermatitis

A facultative anaerobic, Gram-positive, rod-shaped bacterial strain, designated AD045-1ᵀ, was isolated from the stool sample of a 25-month-old male toddler diagnosed with atopic dermatitis. Analysis of the V3 and V4 hypervariable regions of the 16S rRNA gene revealed 100% and 99.8% sequence similarity to Streptococcus anginosus subsp. anginosus DSM 20563ᵀ and Streptococcus anginosus subsp. whileyi CCUG 39159ᵀ, respectively. However, phylogenetic analysis based on full-length 16S rRNA gene sequencing (1,562 bp) showed that strain AD045-1 ^T exhibited the highest sequence similarity to S. anginosus subsp. anginosus DSM 20563 ^T (99.7%), followed by S. anginosus subsp. whileyi CCUG 39159 ^T (99.6%) and "Streptococcus vaginalis" P1L01^T (98.5%). The average nucleotide identity (ANI) values between strain AD045-1 ^T and S. anginosus subsp. anginosus and S. anginosus subsp. whileyi were 94.4-94.7% and 93.4-93.6%, respectively, and the highest in silico DNA-DNA hybridization value with respect to the closest species was 58.1%. Streptococcus hominis NSJ-17 ^T also showed a relatively high ANI value (96.1%) with strain AD045-1 ^T. However, the similarity of 16S rRNA genes was only 98.4% and the dDDH value was 67.3%, which is below the threshold of 70% for species distinction. The major cellular fatty acids of strain AD045-1 ^T were 16:0, 18:1ω7c, and 14:0. Based on phylogenetic, genotypic, and phenotypic data, we propose to classify this isolate as representative of a novel species of the genus Streptococcus, Streptococcus atopica sp. nov., in reference to its isolation from the feces of a toddler with atopic dermatitis, with strain AD045-1 ^T (= BCRC 81461 ^T = NBRC 117137 ^T) as the type strain.