Review article- The structures of E. coli O-polysaccharides antigens. Check the notes in the ppt for detailed explanation

1. The structures of Escherichia
coli O-polysaccharide
antigens
R. Stenutz, A. Weintraub & G. Wildmam

2. Escherichia coli
 Gram negative bacteria
 Family Enterobacteriaceae
 Pathogenic and non pathogenic strains
 Common cause of diarrhea
 Pathotypes- EPEC, ETEC, EIEC,
EHEC, EAEC, DAEC, and UPEC

4. Lipopolysaccharide
structure
 It consists of Lipid A, core
Oligosaccharide (OS), and a
polysaccharide (O-PS)
 Lipid A part is highly conserved in E. coli
 Core OS are of 5 different types R1 to
R4 and K12
 Presently O1-O181 are described.

7. Typing of E coli
 Based on O, H and K antigen.
 Kauffman’s scheme- Serotyping
 Each O antigen defines a serogroup, a
combination of O and H antigens defines
the ‘serotype’.
 Phenotypic assays based on virulence
characteristics for EAEC, DAEC, ETEC,
EIEC.
 NMR spectrum analysis
 Genetic analysis is most reliable.

9. Biosynthesis considerations
 Wzy polymerase dependent pathway,
for heteropolysaccharides. The
repeating unit mostly have NAG residue
at its reducing end only with
modifications in some strains.
 ABC transporter dependent pathway for
homopolymers or have only 2-3
residues in the backbone of the
repeating units

11. O antigen repeating units
 The O antigen consists of 10-25 repeats
of 2-7 residues
 It can be linear, branched or double
branched
 4 residue is most common
 Each residue is found in either α or β
configuration
 Unusual residues are specific for that E.
coli serogroup.

20.  Analysis of the O-antigen structures
revealed that 3-linked N-
acetylglucosamine or N-
acetylgalactosamine residues should be
present at the reducing end.
 In some cases, 4-linked NAG is
observed.
 4 residue backbone is present in half of
the structures.
 Genetic analysis of O antigen cluster will
provide more insight to the structures.

21. Enteropathogenic E. coli
 The hallmark of infections due to EPEC is the
attaching-and-effacing histopathology, which
can be observed in intestinal biopsy
specimens from patients or infected animals.
 EPEC infection is found in infants younger
than 2 years, mostly in developing countries
 The most prevalent serogroups within this
group of E. coli are: O18ac, O20, O25, O26,
O44, O55, O86, O91, O111, O114, O119,
O125ac, O126, O127, O128, O142 and O158

22. Enterotoxigenic E. coli
 Express heat labile toxins, colonizes
surface of bowel mucosa and gives rise to
intestinal secretions, causes mild diarrhea
 Colonization is mediated by one or more
proteinaceous fimbria or fimbrillar
adhesins termed colonization factor
antigens (CFA)
 The most common ETEC serogroups are:
O6, O8, O11, O15, O20, O25, O27, O78,
O128, O148, O149, O159 and O173.

23. Enteroinvasive E. coli
 EIEC strains are biochemically, genetically
and pathogenically closely related to
Shigella spp.
 EIEC penetrates the lining of the large
intestine, to cause inflammation and
mucosal ulceration, causing bacillary
dysentery.
 The most common EIEC serogroups are:
O28ac, O29, O112ac, O124, O136, O143,
O144, O152, O159, O164 and O167.

24. Enterohaemorrhagic E.
coli
 Also called VTEC (‘verotoxigenic E. coli’)or
STEC (‘Shiga toxin-producing E. coli’), as
they express stx gene like Shigella,
causing Haemorrhagic colitis
 adherence phenotype is the intimate or
attaching and effacing adherence mediated
by the eaeA gene again like Shigella
 The most common EHEC serogroups are:
O4, O5, O16, O26, O46, O48, O55, O91,
O98, O111ab, O113, O117, O118, O119,
O125, O126, O128, O145, O157,O172,
O176, O177,O178, O179, O180 and O181

25. Enteroaggregative E. coli
 Do not secrete heat labile toxins and
adhere to HEp-2 cells in an aggregative
manner.
 Colonize intestinal mucosa, predominantly
that of the colon, followed by secretion of
enterotoxins and cytotoxins
 The serogroups that have been identified
within the EAEC group are O3, O7, O15,
O44, O77, O86, O111, O126 and O127.

26. Diffusely Adherent E. coli
 Diffuse adherence in the HEp-2 cell
assay, with the help of fimbria
 Few studies have been carried out to be
able to describe the clinical aspect of
diarrhea caused by DAEC. In one study,
the patients with DAEC had watery
diarrhea without blood and faecal
leukocytes

27. Uropathogenic E. coli
 Epidemiologically associated with
cystitis and acute Kidney infections in
the normal urinary tract.
 There is no single phenotypic profile that
causes urinary tract infections.
 O serogroups – O4, O6, O14, O22, O75
and O83 – cause 75% of these urinary
tract infections.