Listeria monocytogenes endocarditis on a prosthetic heart valve

Listeria monocytogenes endocarditis, an illness with a potentially high mortality developed in a patient with a porcine mitral valve heterograft. After treatment with parenteral ampicillin and streptomycin, blood cultures remained sterile and vegetations noted before treatment cleared. Delay in diagnosis and institution of appropriate antimicrobial therapy may occur because of the diverse morphologic features of L monocytogenes.