paa, originally identified in attaching and effacing Escherichia coli, is also associated with enterotoxigenic E. coli.

Previous studies on virotypes and antimicrobial resistance in a collection of porcine enterotoxigenic Escherichia coli (ETEC) O149 strains from Quebec revealed an increase in the number of multiresistant strains (in particular to tetracycline) and the appearance of new virulence factors with time. Among these factors is paa (for porcine attaching- and effacing-associated), originally identified in a porcine enteropathogenic strain, but also present in enterohemorrhagic E. coli O157:H7. In the present study, the association of paa with other ETEC virulence genes, its conservation and expression were investigated in the O149 ETEC collection. All 37 paa-positive strains possessed estB, elt, astA and faeG, and more than half also carried the estA gene, defining two main virotypes, estA(+) and estA(-). Most strains were tetA- or tetB-positive, or both. paa is carried on high molecular weight plasmids. On tetA plasmids, paa is mostly found with enterotoxin gene estA and autotransporter gene sepA. Paa, a 30 kDa protein, is highly conserved and expressed in these strains. Moreover, paaETEC and porcine EPEC/EHEC contain IS signatures, suggesting that paa could be derived from a common ancestor. All these observations suggest a broader role than previously assessed in virulence for paa.