Evolution of EnterohemorrhagicEscherichia coliHemolysin Plasmids and the Locus for Enterocyte Effacement in Shiga Toxin-ProducingE. coli

Abstract

This study assessed the diversity of the enterohemorrhagicEscherichia coli (EHEC) hemolysin gene (ehxA) in a variety of Shiga toxin-producing E. coli (STEC) serotypes and the relationship between ehxA types and virulence markers on the locus for enterocyte effacement (LEE). Restriction fragment length polymorphism of the ehxA gene and flanking sequences and of the E. coli attaching and effacing (eae) gene was determined for 79 EHEC hemolysin-positive STEC isolates of 37 serotypes. Two main groups of EHEC hemolysin sequences and associated plasmids, which corresponded to the eae-positive and the eae-negative isolates, were delineated. Comparisons of the ehxA gene sequences of representative isolates of each group showed that this gene and the rest of the EHEC hemolysin operon are highly conserved. Digestion of anehxA PCR product with the restriction endonucleaseTaqI showed a unique restriction pattern foreae-negative isolates and another one for isolates of serotypes O157:H7 and O157:NM. A conserved fragment of 5.6 kb with four potential open reading frames was identified on the EHEC hemolysin plasmid of eae-positive STEC. Phylogenetic analysis of a subset of 27 STEC isolates, one enteropathogenic E. coliisolate, and a K-12 reference isolate showed thateae-positive STEC isolates all belong to a single evolutionary lineage and that the EHEC hemolysin plasmid and theehxA gene evolved within this lineage without recent horizontal transfer. However, the eae gene and the LEE appear to have been transferred horizontally within this STEC lineage on several occasions. The reasons for the lack of transfer or maintenance of the LEE in other STEC lineages are not clear and require further study.

Phylogenetic Analysis of Enteroaggregative and Diffusely Adherent Escherichia coli

“…Rhizobium species have been shown to display features of combined horizontal and vertical plasmid transmission (41,44). A similar model is suggested for the large plasmids of EHEC (5). Here, we show that EAEC exhibits a similar pattern of transmission, in which a virulence plasmid is acquired and then stably maintained among clonal descendants.…”

Identification of a haemolysin-like peptide with antibacterial activity using the draft genome sequence ofStaphylococcus epidermidisstrain A487

“…In the current work, we took advantage of high-throughput genome sequence determination methods, allowing the identification of the gene encoding peptide 487 in o 4 weeks. The gene was found to be chromosomally located, as reported previously for staphylococcal haemolysins (Waalwijk et al, 1984;Boerlin et al, 1998;Piccinini & Zecconi, 2001). Some haemolysin genes are plasmid located in Escherichia coli (Avgustin & Grabnar, 2007) and Enterococcus faecalis (Leclercq et al, 1988;Gilmore et al, 1994).…”

Hybrids of Shigatoxigenic and Enterotoxigenic Escherichia coli (STEC/ETEC) Among Human and Animal Isolates in Finland

“…The stx and estIa genes were present in genetically diverse STEC/ETEC strains (minimum similarity being 80%) suggesting the possibility of horizontal transfer of these elements. It is possible that STEC O2:H27 strains circulating in bovine population may obtain additional virulence factors via horizontal gene transfer (Boerlin et al., ).…”