Cell Wall Components and Antigenic Structure
Brucella like any other Gram-negative bacterium contains LPSin the outer cell membrane of the cell walls. But, the LPS of Brucellais different both structurally and functionally fromthat of other Gram-negative bacteria. The LPS of Brucella shows the following unique characteristics:
· The lipid A part of the LPS contains 16-carbon long fatty acids but lacks the 14-carbon myristic acid typical of lipid A of Enterobacteriaceae.
· The polysaccharide O portion of LPS contains an unusual sugar, 4,6-dideoxy-4-formamido-alpha-D-mannopyranoside, which is expressed either as homopolymer of alpha-1,2-linkedsugars(Atype)oras3-alpha-1,2- and2-alpha-1,3-linkedsugars (M type). On the basis of these O polysaccharide linkages, somatic antigens of Brucella are classified into two major types: antigen A and antigen M.
B. abortus has the highest concentration of A antigen (about20 times as much as M antigen), while B. melitensis has the highest concentration of M antigen (about 20 times that of A antigen). B. suis has an intermediate antigenic pattern.
Brucella species show antigenic cross-reaction with Salmonella serotypes N (O: 30 antigen), Escherichia coli (O: 116, O: 157),Vibrio cholerae, Pseudomonas multocida, Yersinia enterocolitica, and Francisella tularensis.
Agglutination and other features of Brucella species are summarized in Table 40-3.