β-Hemolytic Streptococcus anginosus subsp. anginosus causes streptolysin S-dependent cytotoxicity to human cell culture lines in vitro

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