cardiobacterium cardiobacterium cardiobacterium is a gram-negative bacillus (rod-shaped) bacterium commonly grouped with other bacteria into the hacek group. species of cardiobacterium include cardiobacterium hominis and cardiobacterium valvarum. cardiobacterium cardiobacterium hominis on blood agar plate scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: cardiobacteriales family: cardiobacteriaceae genus: cardiobacteriumslotnick & dougherty, 1964 species cardiobacterium hominis cardiobacterium valvarum