Sequence Variations in the Flagellar Antigen Genes fliCH25 and fliCH28 of Escherichia coli and Their Use in Identification and Characterization of Enterohemorrhagic E. coli (EHEC) O145:H25 and O145:H28.

Lothar Beutin,Patrick Fach,Sabine Delannoy

doi:10.1371/journal.pone.0126749

Abstract

Enterohemorrhagic E. coli (EHEC) serogroup O145 is regarded as one of the major EHEC serogroups involved in severe infections in humans. EHEC O145 encompasses motile and non-motile strains of serotypes O145:H25 and O145:H28. Sequencing the fliC-genes associated with the flagellar antigens H25 and H28 revealed the genetic diversity of the fliC H25 and fliC H28 gene sequences in E. coli. Based on allele discrimination of these fliC-genes real-time PCR tests were designed for identification of EHEC O145:H25 and O145:H28. The fliC H25 genes present in O145:H25 were found to be very similar to those present in E. coli serogroups O2, O100, O165, O172 and O177 pointing to their common evolution but were different from fliC H25 genes of a multiple number of other E. coli serotypes. In a similar way, EHEC O145:H28 harbor a characteristic fliC H28 allele which, apart from EHEC O145:H28, was only found in enteropathogenic (EPEC) O28:H28 strains that shared some common traits with EHEC O145:H28. The real time PCR-assays targeting these fliC H25[O145] and fliC H28[O145] alleles allow better characterization of EHEC O145:H25 and EHEC O145:H28. Evaluation of these PCR assays in spiked ready-to eat salad samples resulted in specific detection of both types of EHEC O145 strains even when low spiking levels of 1–10 cfu/g were used. Furthermore these PCR assays allowed identification of non-motile E. coli strains which are serologically not typable for their H-antigens. The combined use of O-antigen genotyping (O145wzy) and detection of the respective fliC H25[O145] and fliC H28[O145] allele types contributes to improve identification and molecular serotyping of E. coli O145 isolates.

Highlights

The ability to produce Shiga (Vero) toxins (Stx) was found to be associated with more than 472 different serotypes (O:H types) of Escherichia coli [1]
enterohemorrhagic E. coli (EHEC) were defined on the basis of the severe clinical picture of the disease they cause, their frequency in outbreaks of disease and the presence of the eae gene encoded by the LEE, and of non-LEE effector genes located on different genomic islands in the strains [3,4,5]
In this work we describe real-time PCR methods for identification of the fliC-genes encoded by EHEC O145:H25 and O145:H28 strains

Summary

Introduction

The ability to produce Shiga (Vero) toxins (Stx) was found to be associated with more than 472 different serotypes (O:H types) of Escherichia coli [1] Many of these Shiga toxin-producing E. coli (STEC) strains are part of the intestinal flora of domestic and wildlife animals and can be found in the environment and as contaminants of food. STEC infections in humans can cause diarrheal disease but only a few number of STEC types may cause more severe illness such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). These latter types of STEC are designated as enterohemorrhagic E. coli (EHEC) [3]. Two other EHEC serotypes, (O45:H2 and O121:H19) were associated with severe disease in humans and included in the panel of EHEC strains (“top-seven”) searched routinely in meat products in the United States [2]

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Conclusion