Polysaccharides of Other Gram-Negative Bacteria

Neisseria meningitidis is a pathogen that causes meningitis in humans. It has an unusual capsular homopolysaccharide that is composed of A -acetyl-D-neuraminic acid. The monosaccharide residue has nine carbons (see Fig. 6.20A). It makes up a family of sugar acids called sialic acids that are N- and 0-substituted derivatives (see Chapter 9). The sialic acids are widely distributed and are primarily found at the ends of the oligosaccharide chains attached to glycoproteins that are especially prevalent in bovine and ovine submaxillary mucins, erythrocytes, and nerve tissues. A -acetyl-D-neuraminic acid is biosynthesized by an aldol condensation of pyruvic acid with N-acetyl-D-mannosamine (see Chapter 10). 

N meningitidis (sero group B) and E, coli K1 both have capsular polysaccharides of poly(A -acetyl-D-neuraminic acid) linked 2 — 8 [193], and both cause meningitis in humans. There is evidence that the polysaccharide is responsible for the infection of tissues [194], possibly by specific cell recognition. The polysaccharide is known as colominic acid (see Fig. 6.20B for the structure). 

N-Acetyl-o-Neuraminic acid pyranose ring form 

N-Acetyl-D-Neuraminic acid open chain form 

The colominic acid from E. coli Bos-12 has an interesting variation in that it has an alternating a-2 8/a-2 9-heterolinked homopolysaccharide of N- 

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