Lineage-Specific Distribution of Insertion Sequence Excision Enhancer in Enterotoxigenic Escherichia coli Isolated from Swine

Abstract

g Insertion sequences (ISs) are the simplest transposable elements and are widely distributed in bacteria; however, they also play important roles in genome evolution. We recently identified a protein called IS excision enhancer (IEE) in enterohemorrhagic Escherichia coli (EHEC) O157. IEE promotes the excision of IS elements belonging to the IS3 family, such as IS629, as well as several other families. IEE-mediated IS excision generates various genomic deletions that lead to the diversification of the bacterial genome. IEE has been found in a broad range of bacterial species; however, among sequenced E. coli strains, IEE is primarily found in EHEC isolates. In this study, we investigated non-EHEC pathogenic E. coli strains isolated from domestic animals and found that IEE is distributed in specific lineages of enterotoxigenic E. coli (ETEC) strains of serotypes O139 or O149 isolated from swine. The iee gene is located within integrative elements that are similar to SpLE1 of EHEC O157. All iee-positive ETEC lineages also contained multiple copies of IS629, a preferred substrate of IEE, and their genomic locations varied significantly between strains, as observed in O157. These data suggest that IEE may have been transferred among EHEC and ETEC in swine via SpLE1 or SpLE1-like integrative elements. In addition, IS629 is actively moving in the ETEC O139 and O149 genomes and, as in EHEC O157, is promoting the diversification of these genomes in combination with IEE.

Simultaneous Presence of Insertion Sequence Excision Enhancer and Insertion Sequence IS 629 Correlates with Increased Diversity and Virulence in Shiga Toxin-Producing Escherichia coli

“…A previous study in swine isolates reported that the presence of either element (IS629 or IEE) is serotype specific (8); results from Kusumoto et al suggest that IEEs spread to different lineages of ETEC and EHEC by horizontal gene transfer with a highly lineagespecific occurrence (8). Our results confirm those findings, as isolates from the same serogroup but different serotypes carry differences in the presence of the two elements.…”

“…Although IS629 was absent in those strains, they did appear to carry IS2, another IS3 family member (data not shown) prevalent among pathogenic E. coli and the excision of which is also enhanced by IEE (8,9).…”

“…The presence of IS629 and IEE was determined by PCR using internal IS629 primers (IS629-TF1 5=-ACT AAA AAT ACT CGT TTT TCC CCC GAA G-3= and IS629-TR1 5=-GGCTGC CAGATCATCGTTTCCGATG-3=; 1,208 bp) and IEE-specific primers (IEEF4 5=-GAT AAA CGA TTT GCC GGG ACG GAA TG-3= and IEER4 5=-GTT TAC CTC CCC CGA TAA TAC CAA TAC-3=, 280 bp) as described previously (8). The 25-l PCR mix contained 1 U of GoTaq DNA polymerase (Promega, Madison, WI), 1ϫ polymerase buffer, 3.5 mM MgCl 2 , 200 M deoxynucleoside triphosphate (dNTP), 200 nM each primer, and ϳ1 ng of template DNA.…”

“…The evolution of pathogens is also influenced by insertion sequence (IS) elements that have contributed to the diversification of enterohemorrhagic Escherichia coli (EHEC) O157 (8,9) (10,11). These IS elements move by inserting several copies of themselves randomly in the same genome, generally by a replicative mode (12).…”

Emergence of a Multidrug-Resistant Shiga Toxin-Producing Enterotoxigenic Escherichia coli Lineage in Diseased Swine in Japan

“…Of the 967 E. coli strains analyzed in the present study (see Table S1 in the supplemental material), the O serogroups of 158 strains had been determined in previous studies (23). The remaining 809 strains were newly analyzed in this study, and the previous data were combined with the new data to conduct a large-scale, nationwide analysis.…”