Overexpression of wbkF gene in Brucella abortus RB51WboA leads to increased O-polysaccharide expression and enhanced vaccine efficacy against B. abortus 2308, B. melitensis 16M, and B. suis 1330 in a murine brucellosis model.

Neha Dabral,Ramesh Vemulapalli,Neeta Jain-Gupta,Nammalwar Sriranganathan,Grant N Burcham,Paulo Lee Ho

doi:10.1371/journal.pone.0213587

Neha Dabral, Ramesh Vemulapalli + Show 4 more

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https://doi.org/10.1371/journal.pone.0213587

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Abstract

Brucella abortus RB51 is an attenuated, stable, spontaneous rough mutant derived in the laboratory from the virulent strain B. abortus 2308. Previous studies discovered that the wboA gene, which encodes a glycosyltransferase required for synthesis of the O-polysaccharide, is disrupted in strain RB51 by an IS711 element. However, complementation of strain RB51 with a functional wboA gene (strain RB51WboA) does not confer it a smooth phenotype but results in low levels of cytoplasmic O-polysaccharide synthesis. In this study, we asked if increasing the potential availability of bactoprenol priming precursors in strain RB51WboA would increase the levels of O-polysaccharide synthesis and enhance the protective efficacy against virulent Brucella challenge. To achieve this, we overexpressed the wbkF gene, which encodes a putative undecaprenyl-glycosyltransferase involved in bactoprenol priming for O-polysaccharide polymerization, in strain RB51WboA to generate strain RB51WboAKF. In comparison to strain RB51WboA, strain RB51WboAKF expressed higher levels of O-polysaccharide, but was still attenuated and remained phenotypically rough. Mice immunized with strain RB51WboAKF developed increased levels of smooth LPS-specific serum antibodies, primarily of IgG2a and IgG3 isotype. Splenocytes from mice vaccinated with strain RB51WboAKF secreted higher levels of antigen-specific IFN-γ and TNF-α and contained more numbers of antigen-specific IFN-γ secreting CD4+ and CD8+ T lymphocytes when compared to those of the RB51 or RB51WboA vaccinated groups. Immunization with strain RB51WboAKF conferred enhanced protection against virulent B. abortus 2308, B. melitensis 16M and B. suis 1330 challenge when compared to the currently used vaccine strains. Our results suggest that strain RB51WboAKF has the potential to be a more efficacious vaccine than its parent strain in natural hosts.

Highlights

Bacteria belonging to the genus Brucella are Gram-negative, facultative intracellular coccobacilli that primarily replicate in the monocyte-macrophage lineage of host cells
The O-PS is an immunodominant component of LPS; infected animals develop antibodies to it. These antiO-PS antibodies play a role in enhancing protection against virulent B. abortus, B. melitensis and B. suis in mouse models of infection [9,10,11,12]
Mice infected with virulent B. abortus 2308, B. melitensis 16M or B. suis 1330 do not develop clinical disease or exhibit any signs of suffering for the duration of the experiments conducted in this study

Summary

Introduction

Bacteria belonging to the genus Brucella are Gram-negative, facultative intracellular coccobacilli that primarily replicate in the monocyte-macrophage lineage of host cells. Smooth LPS protects Brucella from complement-mediated lysis and the microbicidal properties of host phagocytic cells [1, 8]. Smooth Brucella strains are more virulent than their rough counterparts, which are typically attenuated [1,2,3]. The O-PS is an immunodominant component of LPS; infected animals develop antibodies to it. These antiO-PS antibodies play a role in enhancing protection against virulent B. abortus, B. melitensis and B. suis in mouse models of infection [9,10,11,12]. Similar to other intracellular pathogens, cell-mediated immunity (CMI) plays a central role in acquired resistance against brucellosis

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