Comparative Genomics and Infection of Field Clonal Isolates of Biovar 3 Did Not Identify Signature of Host Adaptation.

spp. are responsible for brucellosis, a widespread zoonosis causing reproductive disorders in animals. Species-classification within this monophyletic genus is based on bacteriological and biochemical phenotyping. Traditionally, species are reported to have a preferential, but not exclusive mammalian host. However, this concept can be challenged since many species infect a wide range of animal species. Adaptation to a specific host can be a driver of pathogen variation. It is generally thought that species have highly stable and conserved genomes, however the degree of genomic variation during natural infection has not been documented. Here, we investigated potential genetic diversity and virulence of biovar 3 field isolates obtained from a single outbreak but from different host species (human, bovine, small ruminants). A unique MLVA-16 pattern suggested all isolates were clonal. Comparative genomic analyses showed an almost non-existent genetic diversity among isolates (only one SNP; no architectural rearrangements) and did not highlight any signature specific to host adaptation. Similarly, the strains showed identical capacities to enter and replicate in an model of macrophage infection. In our study, the absence of genomic variability and similar virulence underline that biovar 3 is a broad-host-range pathogen without the need to adapt to different hosts.