Brucella is a genus of Gram-negative bacteria, named after David Bruce (1855-1931). They are small (0.5 to 0.7 by 0.6 to 1.5 µm), nonencapsulated, flagellated, facultatively intracellular coccobacilli. The different species of Brucella are genetically very similar, although each has a slightly different host specificity. Hence, the NCBI taxonomy includes most Brucella species under Brucella melitensis. The many names of brucellosis include (human disease/animal disease):