Neisseria mucosa endocarditis. A case of Neisseria mucosa tricuspid valve endocarditis in an intravenous drug abuser is described. The patient was treated initially with intravenous penicillin G followed by oral penicillin VK but relapsed. He was cured after 4 weeks of combined therapy with penicillin G and gentamicin. In vitro synergy studies performed on the patient's and two other isolates revealed synergy in all three. Thus, combination therapy is recommended for treatment of recalcitrant cases of bacterial endocarditis caused by N. mucosa. 