a family of bacteria (order Eubacteriales) containing small, coccoid to rod-shaped, gram-negative cells which occur singly, in pairs, in short chains, or in groups. The cells may or may not show bipolar staining. Motile and nonmotile species occur; motile cells are peritrichous. V (phosphopyridine nucleotide) and/or X (hemin) factors are sometimes required for growth. Blood serum may be required or may enhance growth. Increased carbon dioxide tension may also favour growth, especially on primary isolation. These organisms are parasites and pathogens which affect warm-blooded animals, including man, rarely cold-blooded animals. It was formerly called Parvobacteriaceae. The type genus is brucella.