Penicillin-sensitive Moraxella prosthetic endocarditis. Near disaster caused by failure to treat with penicillin.

A patient with late prosthetic endocarditis resulting from Moraxella non-liquefaciens is reported. Correct laboratory indentification is of therapeutic importance as Moraxella is often highly sensitive to penicillin. Because of suspected penicillin sensitivity, antibiotics other than penicillin were used, but failed to control the endocarditis. Prompt response occurred when penicillin was given. Penicillin remains by far the most effective antibiotic for the treatment of endocarditis, particularly when affecting prosthetic valves, and caused by organisms sensitive to penicillin.