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The
polysaccharide capsule of Escherichia coli K1 rods and its
importance for pathogenicity of these microorganisms
Abstract:
Many
Escherichia coli strains are covered in a layer of
surface-associated polysaccharide called the capsule. Capsular
polysaccharides represent a major surface antigen, the K antigen,
and more than 80 distinct K serotypes results from structural
diversity in these polymers. One of the most extensively studied
bacterial capsules is the K1 serotype of E. coli. The
K1 capsular polysaccharide of E. coli is an a
2,8-linked homopolymer of sialic acid (NeuNAc). Biosynthesis of the
K1 capsule involves synthesis, activation, and polymerization of
sialic acid subunits into a large polymer that must be transported
across the inner and outer membranes and anchored to the cell
surface. The genes encoding proteins necessary for these events
have been isolated and characterized (kps gene cluster). In
this review, the current understanding of the functions of the kps
gene products is summarized. The K1 capsule is an important
virulence determinant of pathogenic E. coli and
has been shown to be associated with more than 80% of isolates
from E. coli neonatal meningitis as well as the
majority of isolates from neonatal septicaemia and childhood
pyelonephritis. Recent studies with E. coli K1 have
indicated that several microbial determinants such as the S
fimbriae, OmpA, Ibe proteins, AslA, TraJ, and CNF1 contribute
to invasion of brain microvascular endothelial cells, which is
required for successful penetration into the central nervous
system.
1. Capsule
classification of Escherichia coli rods. 2. K1
capsular polysaccharide of E. coli. 3. Biological
role of capsule. 4. Pathogenicity of E. coli K1
strains. 4.1. Meningitis and bacteremia. 4.2. Urinary
tract infection. 5. Summary
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