The New Strains Brucella inopinata BO1 and Brucella Species 83–210 Behave Biologically Like Classic Infectious Brucella Species and Cause Death in Murine Models of Infection

Background. Recently, novel atypicalBrucellastrains isolated from humans and wild rodents havebeen reported. They are phenotypically close to Ochrobactrum species but belong to the genus Brucella, based on genetic relatedness, although genetic diversity is higher among the atypical Brucella strains than between the classic species. They were classified within orclose to the novel speciesBrucella inopinata. However, with the exception ofBrucella microti, the virulence of these novel strains has not been investigated in experimental models of infection. Methods. The type species B. inopinata strain BO1 (isolated from a human) and Brucella species strain 83–210 (isolated from a wild Australian rodent) were investigated. A classic infectious Brucella reference strain, B. suis 1330, was also used. BALB/c, C57BL/6, and CD1 mice models and C57BL/6 mouse bone-marrow-derived macrophages (BMDMs) were used as infection models. Results. Strains BO1 and 83–210 behaved similarly to reference strain 1330 in all mouse infection models: there were similar growth curves in spleens and livers of mice and similar intracellular replication rates in BMDMs. However, unlike strain 1330, strains BO1 and 83–210 showed lethality in the 3 mouse models. Conclusions. The novel atypical Brucella strains of this study behave like classic intracellular Brucella pathogens. In addition, they cause death in murine models of infection, as previously published for B. microti, another recently described environmental and wildlife species.