Distribution of classical and nonclassical virulence genes in enterotoxigenic Escherichia coli isolates from Chilean children and tRNA gene screening for putative insertion sites for genomic islands.

Abstract

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea. Three adhesins (Tia, TibA, EtpA), an iron acquisition system (Irp1, Irp2, and FyuA), a GTPase (LeoA), and an autotransporter (EatA) are ETEC virulence-related proteins that, in contrast to the classical virulence factors (enterotoxins and fimbrial colonization factors) have not heretofore been targets in characterizing isolates from epidemiological studies. Here, we determined the occurrence of these nonclassical virulence genes in 103 ETEC isolates from Chilean children with diarrhea and described their association with O serogroups and classical virulence determinants. Because tia, leoA, irp2, and fyuA are harbored by pathogenicity islands inserted into the selC and asnT tRNA genes (tDNAs), we analyzed the regions flanking these loci. Ten additional tDNAs were also screened to identify hot spots for genetic insertions. Associations between the most frequent serogroups and classical colonization factor (CF)-toxin profiles included O6/LT-STh/CS1-CS3-CS21 (i.e., O6 serogroup, heat-labile [LT] and human heat-stable [STh] enterotoxins, and CFs CS1, -3 and -21), O6/LT-STh/CS2-CS3-CS21, and O104-O127/STh/CFAI-CS21. The eatA and etpA genes were detected in more than 70% of the collection, including diverse serogroups and virulence profiles. Sixteen percent of the ETEC strains were negative for classical and nonclassical adhesins, suggesting the presence of unknown determinants of adhesion. The leuX, thrW, and asnT tDNAs were disrupted in more than 65% of strains, suggesting they are hot spots for the insertion of mobile elements. Sequences similar to integrase genes were identified next to the thrW, asnT, pheV, and selC tDNAs. We propose that the eatA and etpA genes should be included in characterizations of ETEC isolates in future epidemiological studies to determine their prevalence in other geographical regions. Sequencing of tDNA-associated genetic insertions might identify new ETEC virulence determinants.