ABSTRACT
Six species are currently recognized within the genus Brucella: B. melitensis, B. abortus, B. suis, B. neotomae, B. ovis, and B. canis. This classification is mainly based on differences in pathogenicity and in host preferences (sheep and goats, cattle, swine, desert rat, rams, and dogs respectively). Although the six species can be differentiated by conventional phenotypic tests, these species display a high degree of DNA homology in DNA-DNA hybridization assays (> 90% identity). Therefore it has been proposed that the Brucella genus should comprise only one species i.e. B. melitensis and that the other species should be considered as biovars. However, several molecular genotyping methods has been used to show that Brucella species display significant DNA polymorphism allowing the species to be differentiated thereby justifying the current species classification. This is also true for the recent marine mammal Brucella isolates for which two new species names have been proposed, i.e. B. pinnipediae and B. cetaceae, according to the classical criteria of host preferentialism (pinnipeds and cetaceans respectively) and specific molecular markers.
