Characterization of the fate of a rough mutant of Brucella microti in cellulo and in vivo

The new and atypical species Brucella microti shows a fast rate of replication in a macrophage model of infection and has been the first Brucella species described to kill mice in the murine model of infection at a standard dose of inoculation. A spontaneous rough (R) mutant of the species was isolated, and the mutation resulting in the R-phenotype identified by whole-genome sequencing of the strain. Using in cellulo and in vivo models of infection, the goal of the study was to characterize the behavior of this spontaneous mutant and of a defined R-mutant affected in the same gene of O-polysaccharide biosynthesis, in comparison to that of the classical pathogenic species Brucella suis 1330. Given the lethal phenotype of wild-type B. microti in mice, the importance of smooth LPS in virulence of this atypical species can be assessed in vivo, and this first-time study of a R-mutant of an atypical species will yield valuable information on possible specificities in host-pathogen interactions linked to the O-chain of LPS.