Abstract
Brucella 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, Brucella species are reported to have a preferential, but not exclusive mammalian host. However, this concept can be challenged since many Brucella 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 Brucella 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 Brucella melitensis 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 in vitro model of macrophage infection. In our study, the absence of genomic variability and similar virulence underline that B. melitensis biovar 3 is a broad-host-range pathogen without the need to adapt to different hosts.
Highlights
Brucellosis, caused by bacteria of the Brucella genus, is a widespread zoonosis causing reproductive disorders in animals and a debilitating infection in humans
A total of 2,748 Single Nucleotide Polymorphism (SNP) were identified among all studied strains vs. 16M, but only one SNP was observed amongst the seven field strains, in an ovine isolate (Figure 1)
B. melitensis is associated with infection of small ruminants and B. abortus with cattle
Summary
Brucellosis, caused by bacteria of the Brucella genus, is a widespread zoonosis causing reproductive disorders in animals and a debilitating infection in humans. Host Adaptation of Brucella melitensis Biovar 3 wild ruminants (e.g., ibex) (Office International des Epizooties [OIE], 2016) (Garin-Bastuji et al, 2014), and is the major species responsible for human infections. Comparative genomics have allowed us to identify the key steps in the evolution of Brucella from a soil organism to a stealth pathogen. This has involved the acquisition of a battery of virulence factors followed by a toning down of virulence (Wattam et al, 2014). Ke and collaborators suggested that B. melitensis rapidly accumulates mutations during in vivo passage, this observation is not supported by the high levels of sequence conservation seen between the genome sequences available in Genbank (Ke et al, 2012)
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