Phenotypic differentiation of Cardiobacterium hominis, Kingella indologenes and CDC group EF-4

Eleven strains of Cardiobacterium hominis, two strains of Kingella indologenes and six strains of CDC group EF-4 were characterized. Since all three taxa are oxidase-positive, fastidious gram-negative rods with relatively few positive reactions, they may be easily confused in the microbiological laboratory. Common characteristics are acid production from glucose, aerobic growth in semi-solid agar and very slow anaerobic growth. Group EF-4 is distinguished from the other two species by its capacity to produce catalase and its lack of indole production. Cardiobacterium hominis can be distinguished from Kingella indologenes by its ability to ferment mannitol and sorbitol and by differences in enzyme production. The three taxa also differ considerably with regard to morphological and cultural characteristics.