TAXONOMY: cellular organisms -> Bacteria -> Proteobacteria -> Gammaproteobacteria -> Cardiobacteriales -> Cardiobacteriaceae -> Cardiobacterium
Straight rods 0.5–0.75 × 1.0–3.0 µm, with rounded ends. Occasional long filaments, 7.0–35.0 µm may occur. Pleomorphic. Cells are arranged singly, in pairs, in short chains, and in rosette clusters. Gram negative, but retention of crystal violet may occur in the swollen ends or central portions of cells. Nonmotile. Facultatively anaerobic. CO2 is required by some strains on isolation. Aerobic growth is scant unless humidity is elevated. Growth in candle jars or under anaerobic conditions is not dependent on an elevated humidity. Optimum temperature, 30–37°C. Colonies on blood agar are smooth, convex, and opaque. Chemoorganotrophic, having a strictly fermentative type of metabolism. Acid but not gas is produced from fructose, glucose, mannose, sorbitol, mannitol, and sucrose. Lactic acid is the major product of glucose fermentation; smaller amounts of pyruvate, formate, and propionate are formed. Oxidase positive. Catalase negative. Small amounts of indole are formed. Nitrates are not reduced. No growth occurs on MacConkey agar. Urease negative. Ornithine decarboxylase (ODC) negative. Occur in nasal flora of humans; isolated from the blood of humans with bacterial endocarditis.
The mol% G + C of the DNA is: 59–60.
Type species: Cardiobacterium hominis