Recently, novel Brucella strains with phenotypic characteristics that were atypical for strains belonging to the genus Brucella have been reported. Phenotypically many of these strains were initially misidentified as Ochrobactrum spp. Two novel species have been described so far for these strains, i.e., B. microti and B. inopinata, and other strains genetically related to B. inopinata may constitute other novel species as well. In this study, we analyzed the
lipopolysaccharides (LPS) (smooth LPS [S-LPS] and rough LPS [R-LPS]) of these atypical strains using different methods and a panel of
monoclonal antibodies (MAbs) directed against several
epitopes of the Brucella O-
polysaccharide (O-PS) and R-LPS. Among the most striking results, Brucella sp. strain
BO2, isolated from a patient with chronic destructive
pneumonia, showed a completely distinct S-LPS profile in
silver stain gels that looked more similar to that of enterobacterial S-LPS. This strain also failed to react with MAbs against Brucella O-PS
epitopes and showed weak reactivity with anti-R-LPS MAbs. B. inopinata reference strain
BO1 displayed an M-dominant S-LPS type with some heterogeneity relative to the classical M-dominant Brucella S-LPS type. Australian wild rodent strains belonging also to the B. inopinata group showed a classical A-dominant S-LPS but lacked the O-PS common (C)
epitopes, as previously reported for B. suis biovar 2 strains. Interestingly, some strains also failed to react with anti-R-LPS MAbs, such as the B. microti reference strain and B. inopinata
BO1, suggesting modifications in the core-
lipid A moieties of these strains. These results have several implications for serological typing and serological diagnosis and underline the need for novel tools for detection and correct identification of such novel emerging Brucella spp.