Abstract
Papers on Brucella and brucellosis often begin with ‘Brucellosis is one of the world’s most common zoonotic diseases’. However, this just refers to Brucella melitensis, B. abortus and certain B. suis biovars. These are the most commonly isolated Brucella strains because they have been spread across the world by the livestock industry over past centuries. They are also the most common causes of human brucellosis mainly because they are the species that humans are most exposed to.The Brucella genus is much larger than these three species and, in the last 25 years, has rapidly expanded from 6 to 12 recognised species with several more strains not yet assigned officially. The new strains have been isolated from humans, diverse mammals and, more recently, fish, amphibians and reptiles. It is most likely that many more new strains will be identified in the future.Whole genome sequencing has shown that the genus can be divided into two distinct clusters; the ‘classical’ Brucella, including the major zoonotic strains and the ‘atypical’ Brucella containing many of the new isolates. Many of the ‘atypical’ strains are phenotypically distinct form the ‘classical’ strains showing rapid growth, motility, a chemically and antigenically distinct O-antigen and a unique metabolic capacities. These atypical strains highlight the evolutionary path of Brucella from a soil bacterium. Very recently, the taxonomy of the genus Brucella has been complicated by the reclassification of other members of the Brucellaceae to the genus. These bacteria are soil bacteria or endophytes associated with different plants that do not cause a brucellosis like disease. This change is greatly contested by the Brucella research community.Due to their importance to the livestock industry and to human health, most studies concerning the virulence and zoonotic potential of Brucella have been with on B. melitensis, B. abortus and B. suis. In this Keynote Lecture, I will give an overview of how the Brucella genus has expanded and discuss to what extent the new strains represent a threat for animal or human health. I will also comment on the problems associated with the inclusion of non-Brucella strains in the genus.
Contact author: david.o-callaghan@umontpellier.fr
