<prompt> A 28-year-old man with fever persisting for 3 weeks presented with tricuspid valve vegetation. The patient is an intravenous drug abuser. The most common cause of endocarditis in this patient isStreptococcus viridansStaphylococcus aureusEnterococcus fecalisPseudomonas  <response>: Staphylococcus aureus is the most common cause of infective endocarditis among injection drug users. Microbiology of Infective Endocarditis Community-acquired Native valve endocarditis- Viridans group streptococci VGS Healthcare-associated Native valve endocarditis -Staphylococcus aureus Endocarditis in injection drug users- Staphylococcus aureus Early prosthetic valve endocarditis 12 months after surgery- Single most common causative organism: Viridans Streptococci and Overall most common cause: Coagulase-negative staphylococci CoNS Late prosthetic valve endocarditis 12 months after surgery- Single most common causative organism: Viridans Streptococci and Overall most common cause: Coagulase-negative staphylococci CoNS Cardiovascular implantable electronic device CIED- associated endocarditis- Staphylococcus aureus and coagulase-negative Staphylococci CoNS CoNS includes Staphylococcus epidermidis and other coagulase-negative types Streptococci includes Viridans streptococci VGS, Streptococcus gallolyticus previously Streptococcus bovis biotype 1 and other nongroupable and groupable streptococci Reference: Ananthanarayan and Paniker;s Textbook of Microbiology Tenth edition 