Abstract
R. A. Bowden, J. M. Verger, M. Grayon, J. N. Limet and G. Dubray
Laboratoire de Pathologie Infectieuse et Immunologie, Institut National de la Recherche Agronomique, Nouzilly, France.
Brucella strains exhibit either a rough (R) or a smooth (S) colonial phase identifiable by bacteriological methods. This depends on the biosynthesis and translocation to the surface in S but not in R strains, of the O-polysaccharide chain of the lipopolysaccharide (LPS) molecule. B. melitensis biovar 1 strain EP exhibited simultaneously both S and R characteristics in relation to colonial morphology, agglutination by monospecific anti-M and anti-R sera, activity of bacteriophages lytic for rough Brucella spp. (phage R/C) and for smooth B. melitensis (phage Iz). B. melitensis strain EP expressed fewer O-chains with a similar distribution of molecular weights than B. melitensis reference strain 16M by SDS-PAGE and immunoblotting, but higher amounts of R-LPS. Quantitative determination of S-LPS by a turbidimetric latex inhibition immunoassay with monoclonal antibodies confirmed the limited expression of S-LPS in strain EP. As with other gram-negative bacteria, the phenomenon could be attributed to a deficiency in one step of the biosynthetic assembly of the O-chains.