Streptolysin S (SLS) is a small, non-immunogenic, peptide. This means that no commercial antibody against it is available and the peptide is too small for reliable mass spectrometry detection. It is heavily post-translationally modified and is the product of a complex operon. Its exact mode-of-action is still not yet fully clarified. In a previous publication, we were able to show that SLS is neutralized by phosphatidylcholine as well as sphingomyelin liposomes [1]. However, given the poor characterization of SLS, its unavailability from commercial providers and its extremely tedious purification, the mechanistic details of the SLS neutralization will require an extensive a project of its own and are beyond the scope of the current study.
In my opinion, differential inhibition of the SLS activity in GGS supernatant by the liposome preparations is interesting, and may provide new insights, if explored in more detail.