Aetiology

Brucella spp. are Gram-negative, facultative intracellular bacteria. They are coccobacilli measuring 0.6 to 1.5 μm long and 0.5 to 0.7 μm wide. They are generally single, and rarely arranged in groups of two or more.

Ten species are recognized within the genus Brucella: the six ‘classical’ Brucella species, some of which include differ­ent biovars: Brucella abortus (biovars 1, 2, 3, 4, 5, 6, 7, 9), Brucella melitensis (biovars 1, 2, 3), Brucella suis (biovars 1, 2, 3, 4, 5), Brucella ovis, Brucella canis and Brucella neotomae^^x1 and the recently described Brucella ceti and Brucella pinnipediaN∖ Brucella microti(³ and Brucella inopinata⁽⁴⁾.

The classification of the classical species was mainly based on differences in phenotypic characteristics, host preference(s) and in pathogenicity. Distinction between species and biovars is currently performed by differential laboratory tests.