P or Pap fimbriae of avian pathogenic Escherichia coli (APEC) have previously been shown to be important in the pathogenesis of colibacillosis. However, no study has been done to ascertain the effects of deletion of the genes responsible for P fimbrial biogenesis on APEC's in vitro and/or in vivo characteristics. In the present study, all 11 genes of the pap gene cluster were deleted from APEC ...