Streptococcus sputorum, a Novel Member of Streptococcus with Multidrug Resistance, Exhibits Cytotoxicity

We describe the genomic and phenotypic characteristics of a novel member of Streptococcus with multidrug resistance (MDR) isolated from hospital samples. Strains SP218 and SP219 were identified as a novel Streptococcus, S. sputorum, using whole-genome sequencing and biochemical tests. Average nucleotide identity values of strains SP218 and SP219 with S. pseudopneumoniae IS7493 and S. pneumoniae ST556 were 94.3% and 93.3%, respectively. Genome-to-genome distance values of strains SP218 and SP219 with S. pseudopneumoniae IS7493 and S. pneumoniae ST556 were 56.70% (54–59.5%) and 56.40% (52.8–59.9%), respectively. The biochemical test results distinguished these strains from S. pseudopneumoniae and S. pneumoniae, particularly hydrolysis of equine urate and utilization of ribose to produce acid. These isolates were resistant to six major classes of antibiotics, which correlated with horizontal gene transfer and mutation. Notably, strain SP219 exhibited cytotoxicity against human lung epithelial cell line A549. Our results indicate the pathogenic potential of S. sputorum, and provide valuable insights into mitis group of streptococci.