Distribution of the Secondary Type III Secretion System Locus Found in Enterohemorrhagic Escherichia coli O157:H7 Isolates among Shiga Toxin-Producing E. coli Strains

Abstract

The ability of the complete genome sequence of enterohemorrhagic Escherichia coli O157 led to the identification of a 17-kb chromosomal region which contained a type III secretion system gene cluster at min 64.5. This locus contains open reading frames whose amino acid sequences show high degrees of similarity with those of proteins that make up the type III secretion apparatus, which is encoded by the inv-spa-prg locus on a Salmonella SPI-1 pathogenicity island. This locus was designated ETT2 (E. coli type III secretion 2) and consisted of the epr, epa, and eiv genes. ETT2 was found in enteropathogenic E. coli strains and also in some non-O157 Shiga toxin-producing E. coli (STEC) strains, but most of them contained a truncated portion of ETT2. Most O157 isolates had a complete collection of toxin-encoding genes eae and hlyA and the ETT2 locus, while most O26 strains had toxin-encoding genes eae and hlyA genes but an incomplete ETT2 locus. Thus, an intact copy of ETT2 might mark a pathogenic distinction for particular STEC strains. Therefore, the presence of the ETT2 locus can be used for identification of truly pathogenic STEC strains and for molecular fingerprinting of the epidemic strains in humans and animals.Enterohemorrhagic Escherichia coli (EHEC) and Shiga toxin-producing E. coli (STEC) are the most common causes of hemorrhagic colitis, bloody diarrhea, and hemolytic-uremic syndrome and also cause food-borne epidemics in humans (19). STEC is distributed widely in the environment (1, 2). It produces cytotoxin as the main virulence factor but can have a histopathologic effect on intestinal epithelial cells, causing attaching-and-effacing (A/E) lesions. Enteropathogenic E. coli (EPEC), which is a major cause of infant diarrhea in developing countries, has the same ability to cause A/E lesions. These lesions are characterized by localized destruction of brush border microvilli, intimate attachment of the organism to the host cell membrane, and formation of an actin-rich underlying structure in the host cells (5). All genes necessary for the formation of A/E lesions are located in a pathogenicity island termed the locus for enterocyte effacement (LEE) (18). This locus contains genes for structural components of a secretion apparatus that belongs to the type III secretion system, that is, genes for the adhesin intimin and its translocated receptor, Tir (7).The type III secretion system, which is found in many gramnegative pathogens, is responsible for secretion and injection of virulence-associated factors into the cytosol of host cells. The type III apparatus comprises approximately 20 proteins, with most of them located in the inner membrane (6, 24). Most inner membrane proteins are homologous to components of the flagellar biosynthesis apparatuses of both gram-negative and gram-positive bacteria (10). In Salmonella enterica serovar Typhimurium, two independent type III secretion systems encoded by separate chromosomal loci, SPI-1 and SPI-2, have been found (8,22). SPI-1 is required for the invasion of mamma...

The ETT2 Gene Cluster, Encoding a Second Type III Secretion System from Escherichia coli , Is Present in the Majority of Strains but Has Undergone Widespread Mutational Attrition

“…Furthermore, they imply that the essential difference between EHEC and K-12 at this locus is a deletion in K-12 rather than an insertion into the EHEC genome, as claimed by Makino et al (35), and that the originally commensal and now laboratory- …”

“…Three recent studies have shown that the ETT2 gene cluster is found in some pathogenic strains of E. coli in addition to O157:H7 (23,35,40). However, these studies failed to agree on the boundaries of the cluster, were limited in terms of the phylogenetic diversity of the strains they sampled (leading to the erroneous conclusion that ETT2 is largely absent from nonpathogenic strains), and did not describe any ETT2-associated chaperone or translocator genes.…”

“…However, previous authors have disagreed on the boundaries of the cluster: using the Sakai genome nomenclature, Makino et al (35) placed the left boundary at ECs3714, delimiting what they considered to be a 17-kb insertion, while Hartleib et al (23) place the boundary further upstream, at ECs3703 (rmbA/yqeH), making the cluster 29.9 kb in length. To resolve this issue, we used three independent methods to define the boundaries of the island, namely homologies to other TTSS genes, GϩC content, and genomic comparisons ( Several genes that are homologous to components of TTSS gene clusters were found upstream of ECs3714 in the Sakai strain ( Spi-1 [37% identity at the protein level over a 140-amino-acid stretch] [46]).…”

“…on May 9, 2018 by guest http://jb.asm.org/ (24,49), and close homologies have been noted between the proteins encoded by this O-island and those in the S. enterica Spi-1 TTSS (percent identities were recorded by Makino et al [35]). However, previous authors have disagreed on the boundaries of the cluster: using the Sakai genome nomenclature, Makino et al (35) placed the left boundary at ECs3714, delimiting what they considered to be a 17-kb insertion, while Hartleib et al (23) place the boundary further upstream, at ECs3703 (rmbA/yqeH), making the cluster 29.9 kb in length.…”

Arp2/3-independent assembly of actin by Vibrio type III effector VopL

“…New pandemic strains of this pathogen are emerging throughout the world (1). Sequencing of the V. para genome identified two pathogenicity islands encoding type III secretion systems, TTSS1 and TTSS2, the latter associated with virulent, clinical isolates of V. para (2). Iida and colleagues (3,4) have demonstrated that the TTSS on chromosome one (TTSS1) is linked to cytotoxicity in infected tissue culture cells, whereas the TTSS on chromosome two (TTSS2) is associated with enterotoxicity in the rabbit ileal loop model.…”