Escherichia coli K1 and Polysialic Acid

Polysialic acid can be composed of 5-V-acetylneuraminic acid (Neu5Ac), 5-V-glycolylneuraminic acid (Neu5Gc), or deaminated neuraminic acid (KDN) residues, which are usually joined by a2,8, a2,9, or alternating a2,8/a2,9 ketosidic linkages [47-53]. 

coli Kl polysaccharide is composed of a2,8-linked Neu5Ac. Identical capsules have also been fotmd in Neisseria meningitidis serogroup B, Moraxella 

By mimicry of this host structure, polysialic acid encapsulated bacteria evade the human immune system [64]. In contrast to many other capsular polysaccharides, a2,8-linked polysialic acid is a poor immunogen and protects the bacterium from complement-mediated lysis and opsonophagocytosis, and it has been suggested that it enables the bacterium to cross the blood-brain barrier [10, 39, 41, 65-67]. 

The polysialic acid capsule of E. coli K1 is not only an essential virulence factor it also provides an attachment site for specialized K1 bacteriophages. Almost 30 lytic enterobacterial phages specific for E. coli K1 have been isolated, mainly from sewage samples. Interestingly, they have been found to exhibit different morphologies, thus belonging to the three different families of the Caudovirales (Table 1). 

Name Virus family Host strain or lysogen Phage isolation Endosialidase gene cloned Enzyme 

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