25 year old man with 3 weeks fever presented with tricuspid valve vegetation. Most common cause is ? MC cause of Endocorditis in I.V. drug abuses

Staph aureus "Endocarditis among i.v. drug users especially when infection involves the tricuspid valve is commonly caused by S. aureus strains many of which are methicillin resistant". Left sided valve infection in addicts has a more varied etiology and involve abnormal valves often ones damaged by prior episodes of endocarditis. A number of these cases are caused by Pseudomonas aeruginosa and candida species and sporadic cases are due to unusual organisms such as Bacillus lactobacillus and corynebacterium species.