Diphtheroid prosthetic valve endocarditis. A study of clinical features and infecting organisms.

The clinical features of 19 patients with prosthetic valve endocarditis due to diphtheroids were studied. Infection was noted within 60 days of cardiac surgery in 12 (63 percent) patients. Prosthetic dysfunction and infection of the valve annulus was common (74 percent). Agar dilution minimal inhibitory concentrations for 18 diphtheroids isolated from patients with prosthetic valve endocarditis indicated that 88 percent were susceptible to gentamicin, amikacin, streptomycin, erythromycin and tetracycline; all strains were susceptible to vancomycin. In time-kill studies vancomycin was highly bactericidal as was gentamicin for susceptible strains. For gentamicin-susceptible strains, penicillin-gentamicin combinations were synergistic regardless of the susceptibility of the strains to penicillin. Bactericidal synergy of penicillin-gentamicin combinations was not seen with gentamicin-resistant strains. The biochemical and physiologic features of 20 strains were studied; with the exception of colonial morphology, 18 strains were found to be similar. Four strains were classified as belonging to the group JK by the Center for Disease Control (CDC) and 14 other strains fulfilled CDC criteria for group JK diphtheroids. A technique and criteria for single disc diffusion susceptibility testing are suggested.