AUTHOR=Sidhu-Muñoz Rebeca S. , Tejedor Carmen , Vizcaíno Nieves 

TITLE=The Three Flagellar Loci of Brucella ovis PA Are Dispensable for Virulence in Cellular Models and Mice

JOURNAL=Frontiers in Veterinary Science

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2020.00441

DOI=10.3389/fvets.2020.00441

ISSN=2297-1769

ABSTRACT=<p><italic>Brucella ovis</italic> is a facultative intracellular bacterium that causes a non-zoonotic ovine brucellosis mainly characterized by male genital lesions and is responsible for important economic losses in sheep farming areas. Studies about the virulence mechanisms of <italic>Brucella</italic> have been mostly performed with smooth (bearing O-polysaccharide in lipopolysaccharide) zoonotic species, and those performed with <italic>B. ovis</italic> have revealed similarities but also relevant differences. Except for few strains recently isolated from unconventional hosts, <italic>Brucella</italic> species are non-motile but contain the genes required to assemble a flagellum, which are organized in three main loci of about 18.5, 6.4, and 7.8 kb. Although these loci contain different pseudogenes depending on the non-motile <italic>Brucella</italic> species, smooth <italic>B. melitensis</italic> 16M builds a sheathed flagellum under particular culture conditions and requires flagellar genes for virulence. However, nothing is known in this respect regarding other <italic>Brucella</italic> strains. In this work, we have constructed a panel of <italic>B. ovis</italic> PA mutants defective in one, two or the three flagellar loci in order to assess their role in virulence of this rough (lacking O-polysaccharide) <italic>Brucella</italic> species. No relevant differences in growth, outer membrane-related properties or intracellular behavior in cellular models were observed between flagellar mutants and the parental strain, which is in accordance with previous results with <italic>B. melitensis</italic> 16M single-gene mutants. However, contrary to these <italic>B. melitensis</italic> mutants, unable to establish a chronic infection in mice, removal of the three flagellar loci in <italic>B. ovis</italic> did not affect virulence in the mouse model. These results evidence new relevant differences between <italic>B. ovis</italic> and <italic>B. melitensis</italic>, two species highly homologous at the DNA level and that cause ovine brucellosis, but that exhibit differences in the zoonotic potential, pathogenicity and tissue tropism.</p>