The new species Brucella microti replicates in macrophages and causes death in murine models of infection

Background. The recent isolation of Brucella microti from the common vole, the red fox, and the soil raises the possibility of an eventual reemergence of brucellosis in Europe. In this work, the pathogenic potential of this new Brucella species in both in vitro and in vivo models of infection was analyzed.

Methods. The ability of B. microti (as compared to that of the closely related species Brucella suis) to replicate in human macrophages and in human and murine macrophage-like cells was determined. The behavior of B. microti and B. suis was evaluated in vivo in murine models of infection with Balb/c, CD1, and C57BL/6 mice.

Results.B. microti showed an enhanced capacity for intramacrophagic replication compared with that of B. suis. Surprisingly, and in contrast to other species of Brucella, 105 colony-forming units of B. microti killed 82% of Balb/c mice within 7 days. Infection of spleen and liver with B. microti peaked at day 3, compared with B. suis infection, which peaked at day 7. Sublethal doses of B. microti induced good protection against a subsequent challenge with lethal doses.

Conclusions. In experimental cellular and murine infections, B. microti exhibited a high pathogenic potential, compared with other Brucella species.