Non-curliation of Escherichia coli O78 : K80 isolates associated with IS1 insertion in csgB and reduced persistence in poultry infection

The elaboration of curli fimbriae by Escherichia coli is associated with th e development of a lacy colony morphology when groan on colonisation factor antigen agar at 25 degrees C. Avian colisepticaemia E. coli isolates scree ned for curliation by this culture technique showed lacy and smooth colonia l morphologies and the genetic basis of the non-curliated smooth colonial p henotype was analysed. Two smooth E, coli O78:K80 isolates possessed about 40 copies of the IS1 element within their respective genomes of which one c opy insertionally inactivated the csgB gene, the nucleator gene for curli f ibril formation. One of these two isolates also possessed a defective rpoS gene which is a known regulator of curli expression. In the day-old chick m odel, both smooth isolates were as invasive as a known virulent O78:K80 iso late as determined by extent of liver and spleen colonisation post oral ino culation but were less persistent in terms of caecal colonisation. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Sc ience B.V. All rights reserved.