afa-8 Gene Cluster Is Carried by a Pathogenicity Island Inserted into the tRNA Phe of Human and Bovine Pathogenic Escherichia coli Isolates

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Abstract
We recently described a new afimbrial adhesin, AfaE-VIII, produced by animal strains associated with diarrhea and septicemia and by human isolates associated with extraintestinal infections. Here, we report that the afa-8 operon, encoding AfaE-VIII adhesin, from the human blood isolate Escherichia coli AL862 is carried by a 61-kb genomic region with characteristics typical of a pathogenicity island (PAI), including a size larger than 10 kb, the presence of an integrase-encoding gene, the insertion into a tRNA locus ( pheR ), and the presence of a small direct repeat at each extremity. Moreover, the G+C content of the afa-8 operon (46.4%) is lower than that of the E. coli K-12/MG1655 chromosome (50.8%). Within this PAI, designated PAI I AL862 , we identified open reading frames able to code for products similar to proteins involved in sugar utilization. Four probes spanning these sequences hybridized with 74.3% of pathogenic afa-8 -positive E. coli strains isolated from humans and animals, 25% of human pathogenic afa-8 -negative E. coli strains, and only 8% of fecal strains ( P = 0.05), indicating that these sequences are strongly associated with the afa-8 operon and that this genetic association may define a PAI widely distributed among human and animal afa-8 -positive strains. One of the distinctive features of this study is that E. coli AL862 also carries another afa-8 -containing PAI (PAI II AL862 ), which appeared to be similar in size and genetic organization to PAI I AL862 and was inserted into the pheV gene. We investigated the insertion sites of afa-8 -containing PAI in human and bovine pathogenic E. coli strains and found that this PAI preferentially inserted into the pheV gene.