Cardiobacterium valvarum

The only other identified Cardiobacterium species is Cardiobacterium hominis. Cardiobacterium species are Gram-negative, pleomorphic rod-shaped bacteria that are catalase-negative and oxidase-positive. When compared morphologically, the two Cardiobacterium species are indistinguishable in culture and Gram stain; however, the two differ in growth patterns: C. valvarum is more fastidious than C. hominis, and is non-hemolytic. C. valvarum is also differentiated by the fact that the species does not produce indole.^[1]

Isolates of C. valvarum show optimal growth by day 3 under standard 5% CO₂ incubation conditions on 5% sheep blood, but scant growth on chocolate agar.^{[citation needed]}

Members of the HACEK group are difficult to identify through conventional methods. 16S ribosomal RNA genotyping is the necessary method of identifying C. valvarum^[2]. C.valvarum bears numerous phenotypic similarities with Pasteurella multocida and is therefore commonly misidentified. The phenylphosphonate reaction and Maldi-TOF mass spectrometry can be used to distinguish the two species.

Cardiobacterium species are broadly susceptible to beta-lactam, trimethoprim-sulfamethoxazole, fluoroquinolones, and aztreonam. Current clinical guidelines recommend that C. valvarum infection be treated with a 4-week course of ceftriaxone or ciprofloxacin.^[3]