Shiga Toxin–producing Escherichia coli Strains Negative for Locus of Enterocyte Effacement

Hybrid isolates of Shiga toxin-producing Escherichia coli (STEC) and enterotoxigenic E. coli (ETEC) encoding heat-stable enterotoxin (ST) are being reported with increasing frequency from a variety of sources. However, information regarding the plasmids that these strains harbor is scarce. In this study, we sequence and characterize a plasmid, p7v, from the STEC/ETEC hybrid strain 7v. Whole-genome phylogenetic analyses of STEC/ETEC hybrid strains and prototype E. coli isolates of other pathotypes placed 7v in the Escherichia sp. cryptic lineage 1 (CL1) clade. The complete plasmid, p7v, was determined to be 229,275 bp and encodes putative virulence factors that are typically carried on STEC plasmids as well as those often carried on ETEC plasmids, indicating that the hybrid nature of the strain extends beyond merely encoding the two toxins. Plasmid p7v carries two copies of sta with identical sequences, which were discovered to be divergent from the sta sequences found in the prototype human ETEC strains. Using a nomenclature scheme based on a phylogeny constructed from sta and stb sequences, the sta encoded on p7v is designated STa4. In silico analysis determined that p7v also encodes the K88 fimbria, a colonization factor usually associated with porcine ETEC plasmids. The p7v sequence and the presence of plasmid-encoded virulence factors are compared to those of other STEC/ETEC CL1 hybrid genomes and reveal gene acquisition/loss at the strain level. In addition, the interrogation of 24 STEC/ETEC hybrid genomes for identification of plasmid replicons, colonization factors, Stx and ST subtypes, and other plasmid-encoded virulence genes highlights the diversity of these hybrid strains. IMPORTANCEHybrid Shiga toxin-producing Escherichia coli/enterotoxigenic Escherichia coli (STEC/ETEC) strains, which have been isolated from environmental, animal, and human clinical samples, may represent an emerging threat as food-borne pathogens. Characterization of these strains is important for assessing virulence potential, aiding in the development of pathogen detection methods, and understanding how the hybrid strains evolve to potentially have a greater impact on public health. This study represents, to our knowledge, both the first characterization of a closed plasmid sequence from a STEC/ETEC hybrid strain and the most comprehensive phylogenetic analysis of available STEC/ETEC hybrid genomes to date. The results demonstrate how the mobility of plasmid-associated virulence genes has resulted in the creation of a diverse plasmid repertoire within the STEC/ ETEC hybrid strains. Pathogenic Escherichia coli strains are categorized into pathotypes or pathovars (pathogenic variants) based on virulenceassociated genes whose expression contributes to particular disease symptoms in the human host (1). The virulence-associated genes that are unique to a pathotype have been used as molecular markers to define the pathotype of a given E. coli isolate. Two E. coli pathotypes that cause a significant burden of illness throughout ...

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Hybrid Shiga Toxin-Producing and Enterotoxigenic Escherichia sp. Cryptic Lineage 1 Strain 7v Harbors a Hybrid Plasmid

Leonard

Mammel

Rasko

et al. 2016

“…The LEE island is not present in all STEC strains. Prior studies have found that EHEC is more commonly associated with severe clinical cases (6); however, LEEnegative STEC strains have been linked to severe clinical cases as well as to outbreaks (7). STEC is often acquired by consuming contaminated food or water (8), and cattle are viewed as the most important animal reservoirs (9).…”

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confidence: 99%

Diverse Virulence Gene Content of Shiga Toxin-Producing Escherichia coli from Finishing Swine

Tseng

Fratamico

Bagi

et al. 2014

dShiga toxin-producing Escherichia coli (STEC) infections are a critical public health concern because they can cause severe clinical outcomes, such as hemolytic uremic syndrome, in humans. Determining the presence or absence of virulence genes is essential in assessing the potential pathogenicity of STEC strains. Currently, there is limited information about the virulence genes carried by swine STEC strains; therefore, this study was conducted to examine the presence and absence of 69 virulence genes in STEC strains recovered previously from finishing swine in a longitudinal study. A subset of STEC strains was analyzed by pulsed-field gel electrophoresis (PFGE) to examine their genetic relatedness. Swine STEC strains (n ‫؍‬ 150) were analyzed by the use of a high-throughput real-time PCR array system, which included 69 virulence gene targets. Three major pathotypes consisted of 16 different combinations of virulence gene profiles, and serotypes were determined in the swine STEC strains. The majority of the swine STEC strains (n ‫؍‬ 120) belonged to serotype O59:H21 and carried the same virulence gene profile, which consisted of 9 virulence genes: stx 2e , iha, ecs1763, lpfA O113 , estIa (STa), ehaA, paa, terE, and ureD. The eae, nleF, and nleH1-2 genes were detected in one swine STEC strain (O49:H21). Other genes encoding adhesins, including iha, were identified (n ‫؍‬ 149). The PFGE results demonstrated that swine STEC strains from pigs raised in the same finishing barn were closely related. Our results revealed diverse virulence gene contents among the members of the swine STEC population and enhance understanding of the dynamics of transmission of STEC strains among pigs housed in the same barn.

“…Well-known EHEC serotypes such as O157:H7, O26:H11, and O111:H8 all have eae and have caused severe disease. However, there are LEE-negative EHEC strains, such as O113:H21, that do not have eae but were first implicated in HUS in 1983 (4) and also caused a cluster of HUS cases in Australia in 1998 (5,6). Since O113:H21 strains are eae negative, they are postulated to have other binding factors and virulence genes (7).…”

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confidence: 99%

Genetic Diversity and Virulence Potential of Shiga Toxin-Producing Escherichia coli O113:H21 Strains Isolated from Clinical, Environmental, and Food Sources

Feng

Delannoy

Lacher

et al. 2014

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h Shiga toxin-producing Escherichia coli strains of serotype O113:H21 have caused severe human diseases, but they are unusual in that they do not produce adherence factors coded by the locus of enterocyte effacement. Here, a PCR microarray was used to characterize 65 O113:H21 strains isolated from the environment, food, and clinical infections from various countries. In comparison to the pathogenic strains that were implicated in hemolytic-uremic syndrome in Australia, there were no clear differences between the pathogens and the environmental strains with respect to the 41 genetic markers tested. Furthermore, all of the strains carried only Shiga toxin subtypes associated with human infections, suggesting that the environmental strains have the potential to cause disease. Most of the O113:H21 strains were closely related and belonged in the same clonal group (ST-223), but CRISPR analysis showed a great degree of genetic diversity among the O113:H21 strains.