The Epitopic and Structural Characterization of Brucella suis Biovar 2 O-Polysaccharide Demonstrates the Existence of a New M-Negative C-Negative Smooth Brucella Serovar

Abstract

The brucellae are Gram-negative bacteria that cause an important zoonosis. Studies with the main Brucella species have shown that the O-antigens of the Brucella smooth lipopolysaccharide are α-(1→2) and α-(1→3)-linked N-formyl-perosamine polysaccharides that carry M, A and C (A = M, A>M and A<M) epitopes relevant in serodiagnosis and typing. We report that, in contrast to the B. suis biovar 1 O-antigen used as a reference or to all described Brucella O-antigens, B. suis biovar 2 O-antigen failed to bind monoclonal antibodies of C (A = M), C (M>A) and M specificities. However, the biovar 2 O-antigen bound monoclonal antibodies to the Brucella A epitope, and to the C/Y epitope shared by brucellae and Yersinia enterocolitica O:9, a bacterium that carries an N-formyl-perosamine O-antigen in exclusively α-(1→2)-linkages. By 13C NMR spectroscopy, B. suis biovar 1 but not B. suis biovar 2 or Y. enterocolitica O:9 polysaccharide showed the signal characteristic of α-(1→3)-linked N-formyl-perosamine, indicating that biovar 2 may altogether lack this linkage. Taken together, the NMR spectroscopy and monoclonal antibody analyses strongly suggest a role for α-(1→3)-linked N-formyl-perosamine in the C (A = M) and C (M>A) epitopes. Moreover, they indicate that B. suis biovar 2 O-antigen lacks some lipopolysaccharide epitopes previously thought to be present in all smooth brucellae, thus representing a new brucella serovar that is M-negative, C-negative. Serologically and structurally this new serovar is more similar to Y. enterocolitica O:9 than to other brucellae.

Diagnostic performance of serological tests for swine brucellosis in the presence of false positive serological reactions

“…Although the origin of the problem has not been fully investigated, Y. enterocolitica O:9 is considered the main cause of FPSR in pigs in the EU (Thibodeau et al, 2001;EFSA, 2009). This serotype carries an O-PS chemically and serologically indistinguishable from the O-PS of B. suis biovar 2 (Zaccheus et al, 2013). Thus, it is not surprising that none of the S-LPS tests evaluated here or in previous works Nielsen et al, 2006) fully differentiates brucellosis from FPSR.…”

Monoclonal Antibody-Defined Specific C Epitope of Brucella O-Polysaccharide Revisited

“…In agreement with this observation, a recent structural study on the O chain of B. suis bv. 2, which lacks this epitope (2), revealed the absence of the ␣-1,3-linkage in this particular O chain (17). The present study provides direct evidence that this Brucellaspecific O chain linkage is essential to recognition by such antibodies.…”

Improved Serodiagnosis of Bovine Brucellosis by Novel Synthetic Oligosaccharide Antigens Representing the Capping M Epitope Elements of Brucella O-Polysaccharide

“…The proportion of each linkage type in different strains of Brucella appears to vary from 0% to 20% frequency of ␣(1¡3) linkage types, with the remainder being ␣(1¡2) types. Notably, only the B. suis biovar 2 type strain has been found to be devoid of ␣(1¡3) links (10).…”