β-Hemolytic subsp. causes streptolysin S-dependent cytotoxicity to human cell culture lines .

Streptococcus anginosus subsp. (SAA) is one of the opportunistic pathogens in humans that inhabits the oral cavity. The type strain of SAA, NCTC10713, showed clear β-hemolysis on blood agar plates, and the sole β-hemolytic factor revealed two streptolysin S (SLS) molecules. SLS is well known as the peptide hemolysin produced from the human pathogen and shows not only hemolytic activity on erythrocytes but also cytotoxic activity in cell culture lines and , such as in a mouse infection model. However, no cytotoxic activity of SLS produced from β-hemolytic SAA (β-SAA) has been reported so far. In this study, the SLS-dependent cytotoxicity of the β-SAA strains including the genetically modified strains was investigated . The SLS-producing β-SAA showed cytotoxicity in human cell culture lines under the co-cultivation condition and it was found that this cytotoxicity was caused by the SLS secreted into the extracellular milieu. The results from this study suggest that the SLS produced from β-SAA might indicate the cytotoxic potential similar to that of the SLS from and the SLS-producing β-SAA would be recognized as "a wolf in sheep's clothing" More attention will be paid to the pathogenicity of β-hemolytic Anginosus group streptococci.