Using passive agglutination, Kunin detected the O-antigen found in the lipopolysaccharide (LPS) of E. coli.
One of the sera, O14, reacted to an antigen found in a large range of E. coli strains.
[1] The polysaccharide of the enterobacterial common antigen (ECA) is composed of repeating units of a trisaccharide.
[1][5][4] Regardless of the length, the polysaccharide is attached to a diacylglycerol with a phosphodiester bond and sits on the outer membrane of the bacterium.
Like the ECAPG, the ECALPS sits on the outer membrane of the bacterium and is attached to a lipid.
The details of the synthesis are as follows:[1][7][6] Step 1: WecA takes GlcNAc from UDP-GlcNAc and attaches GlcNAc-1-phosphate to an isoprenoid carrier.
The lipid carrier is returned to the cytoplasmic side of the membrane to create another ECA trisaccharide unit.
Step 12: The growing ECA chain is stopped at the correct length by WzzE through an unknown mechanism.
The product of these 12 steps is a long chain of ECA units attached to an isoprenoid lipid carrier.
The final product, ECAPG, is an ECA polymer linked by a phosphodiester bond to a diacylglycerol.
[1] To make ECALPS, WaaL, takes the ECA polysaccharide from the isoprenoid carrier and gives it to the core oligosaccharide of LPS.
It has been previously established that ECACYC is synthesized in the periplasm and that this mechanism involves WzzE.
[1] Enterobacterales species that have been cultured for prolonged periods show a significant reduction in O-chain synthesis while maintaining ECA stability.
Several gene-knockout experiments show that upon altering genes participating in the synthesis of ECA, new sensitivities are observed.
ECA antibodies have been detected in human serum after infection by E. coli, Yersinia enterocolitica O3 strains, or Proteus mirabilis-associated arthritis patients.
[1] Several studies have sought to identify how significant a role the ECA plays in pathogenicity, even under experimental conditions, the protection offered by an antibody response was slight and temporary in both active and passive immunization.