Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Role of the protein kinase etk in AEEC virulence

Escherichia coli produces polysaccharide capsules that, based on their mechanisms of synthesis and assembly, have been classified into four groups. The group 4 capsule polysaccharide is frequently identical to that of the cognate LPS O side-chain and has, therefore, also been termed the O-antigen capsule. The genes involved in the assembly of the group 1, 2 and 3 capsules have been described, but those required for the assembly of group 4 capsule remained obscure. We found that enteropathogenic E. coli (EPEC) produces group 4 capsule and we identified an operon containing seven genes: ymcD, ymcC, ymcB, ymcA, yccZ, etp and etk, which are required for formation of the capsule.

The encoded proteins appear to constitute a polysaccharide secretion system. The group 4 capsule operon is absent from the genomes of enteroaggregative E. coli and uropathogenic E. coli. E. coli K12 contains the group 4 capsule operon, but does not express it, because of the presence of IS1 at its promoter region. In contrast, EPEC, enterohemorrhagic E. coli (EHEC), and Shigella possess an intact group 4 capsule operon. We recently found that all the tested EPEC serotypes, including O111, O119, O142, and O55, and the closely related entrohemorrhagic E. coli serotype O157, form group 4 capsule and/or express Etk. This correlation suggests that group 4 capsule play a role in the virulence of these closely related pathogens.

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