Severe soft tissue infection caused by a non-hemolytic Streptococcus pyogenes strain with a premature stop mutation in sagC gene

We recovered a non-hemolytic S. pyogenes strain from a severe soft tissue infection that required surgical intervention. In order to define the molecular mechanism of this phenotype, we searched for deletions in the slo gene and sag operon of Streptococcus pyogenes encoding the oxygen-dependent labile streptolysin O (SLO) and the oxygen-stable streptolysin S (SLS), respectively. While there was no deletion in the slo gene, we detected a point mutation in sagC gene that resulted in a premature stop codon (478C-478T). Since SagC is required for efficient posttranslational modification of the structural SLS-precursor SagA, we conclude that the point mutation in sagC results in the non-hemolytic phenotype of our isolate. This is the first report that traces the non-hemolytic phenotype back to a point mutation in the sagC gene. Furthermore, to the best of our knowledge our case demonstrates for the first time that a severe soft tissue infection can be caused by a non-hemolytic S.pyogenes strain.