Cardiobacterium hominis endocarditis: description of two patients and characterization of the organism.

Two cases of endocarditis caused by Cardiobacterium hominis are reported. In both instances infection was subacute and characterized by (i) implantation on abnormal valves, (ii) chronic course lasting weeks to months before recognition, and (iii) rapid clinical and bacteriological response to penicillin, as well as other antibiotics commonly used to treat infections caused by gram-negative bacilli. Our isolates of C. hominis are compared with strains in the National Institutes of Health culture collection. Optimal growth requires yeast extract and incubation at 37 degrees C with increased humidity and supplemental CO2. The production of indole, a positive oxidase reaction, and characteristic sugar fermentation distinguish C. hominis from other slow-growing, gram-negative bacilli.