Class 1 integrons and their conjugal transfer with and without virulence-associated genes in extra-intestinal and intestinal Escherichia coli of poultry

Multiple-drug resistance in enteric bacteria is frequently associated with integrons. To determine whether integrons may play a role in avian pathogenic Escherichia coli, isolates of extra-intestinal (n = 27) and intestinal (n = 40) E. coli from dead chicks and turkey poults were analysed for the presence of class 1 integrons and of the virulence-associated genes iss, tsh and colV. Eleven extra-intestinal strains possessed a 1.0 kb class 1 integron with a variable region of aadA1 and were resistant to tetracycline. These traits were indicative of the presence of the Tn21 transposon, which was confirmed by polymerase chain reaction. All extra-intestinal strains had the colV, iss and tsh genes, but none of these genes were cotransferred with the 1.0 kb integron when conjugal transferability was tested. The integron content of the intestinal strains showed considerable variability: one or two of four different class 1 integrons, which varied from 1.0 to 2.4 kb in size, were detected in the 11 strains. The aadA7 gene of the 1.0 kb integron, the dfrA1-aadA1 genes of the 1.6 kb integron and the folA-catB3-aadA5 genes of the 2.4 kb integron were identical to those described by other workers. However, the orfIN682-dhfrV-orfD gene cassette arrangement of the 1.5 kb integron of an intestinal strain of serogroup O5 had no similarity to any previously reported integrons. Conjugal transfer of the 1.6 and 2.4 kb integrons was successful, and in a serogroup O33 intestinal E. coli strain the iss gene was apparently cotransferred with a 1.6 kb integron. The 1.0 and 1.5 kb integrons were not transferable. Our data suggest that intestinal E. coli strains of poultry may be a reservoir for emerging multiresistant strains of avian pathogenic E. coli.