A 62-year-old man with a 30-year history of rheumatic heart disease presented with episodes of fever and chills, along with worsening signs of congestive heart failure. On examination, purpuric skin rashes were observed.

He had had a tooth removed some weeks before. 

An endocarditis was suspected. Blood cultures were taken.

In this particular patient the causative organism of the endocarditis  was: