Does lipopolysaccharide morphology (smooth or rough) of Brucella abortus vaccine strains influence the potency or efficacy of the vaccine?

Brucella abortus exhibits the dissociation phenomenon, in which naturally smooth samples lose the O chain of lipopolysaccharide (LPS) and become rough, associated with changes in colony shape, culture characteristics, cell morphology, immunological reactions, biochemical reactions and, possibly, virulence. However, the significance and impact of S-R dissociation in cultures (in vitro) or even in vivo is unclear, especially considering that rough samples have already been isolated from clinical samples in different hosts and, also, are successfully used as vaccine strains. Thus, the objective of this study was to review the literature on Brucella spp. LPS to better understand the impact of the LPS morphology in B. abortus in the vaccinal efficacy. The available information indicates that is undeniable that LPS is related to virulence modulation and inducing immunity in the natural hosts of Brucella spp. However, the continuous emergence of rough variants in vivo (infection) or in vitro (cultivation of the microorganism) suggests that this phenotype is part of the biology of the agent and may confer some survival advantage to the bacteria. In fact, for some samples, the permanent or temporary loss of the O chain (O-PS), whether natural or induced, did not necessarily imply a decrease in virulence, immunogenicity, or post-challenge induced protection, since results in both directions were observed in the literature, depending mainly on the parental samples used and the silenced genes. Thus, it is concluded that the emergence of variants related to the smooth/rough LPS of a sample of B. abortus does not necessarily imply changes in the virulence/immunogenicity of that sample and, consequently, in vaccine potency or efficacy, in case of vaccine strains.