The structures of Escherichia coli O-polysaccharide antigens

R. Stenutz, A. Weintraub & G. Wildmam

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

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.

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.

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

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.

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.

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

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.

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.

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

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.

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

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.