Proteins other than the locus of enterocyte effacement-encoded proteins contribute to Escherichia coli O157:H7 adherence to bovine rectoanal junction stratified squamous epithelial cells.

Indira T Kudva,Bryan Krastins,Robert W Griffin,Stephen B Calderwood,Manohar John,David A Sarracino

doi:10.1186/1471-2180-12-103

Abstract

BackgroundIn this study, we present evidence that proteins encoded by the Locus of Enterocyte Effacement (LEE), considered critical for Escherichia coli O157 (O157) adherence to follicle-associated epithelial (FAE) cells at the bovine recto-anal junction (RAJ), do not appear to contribute to O157 adherence to squamous epithelial (RSE) cells also constituting this primary site of O157 colonization in cattle.ResultsAntisera targeting intimin-γ, the primary O157 adhesin, and other essential LEE proteins failed to block O157 adherence to RSE cells, when this pathogen was grown in DMEM, a culture medium that enhances expression of LEE proteins. In addition, RSE adherence of a DMEM-grown-O157 mutant lacking the intimin protein was comparable to that seen with its wild-type parent O157 strain grown in the same media. These adherence patterns were in complete contrast to that observed with HEp-2 cells (the adherence to which is mediated by intimin-γ), assayed under same conditions. This suggested that proteins other than intimin-γ that contribute to adherence to RSE cells are expressed by this pathogen during growth in DMEM. To identify such proteins, we defined the proteome of DMEM-grown-O157 (DMEM-proteome). GeLC-MS/MS revealed that the O157 DMEM-proteome comprised 684 proteins including several components of the cattle and human O157 immunome, orthologs of adhesins, hypothetical secreted and outer membrane proteins, in addition to the known virulence and LEE proteins. Bioinformatics-based analysis of the components of the O157 DMEM proteome revealed several new O157-specific proteins with adhesin potential.ConclusionProteins other than LEE and intimin-γ proteins are involved in O157 adherence to RSE cells at the bovine RAJ. Such proteins, with adhesin potential, are expressed by this human pathogen during growth in DMEM. Ongoing experiments to evaluate their role in RSE adherence should provide both valuable insights into the O157-RSE interactions and new targets for more efficacious anti-adhesion O157 vaccines.

Highlights

In this study, we present evidence that proteins encoded by the Locus of Enterocyte Effacement (LEE), considered critical for Escherichia coli O157 (O157) adherence to follicle-associated epithelial (FAE) cells at the bovine recto-anal junction (RAJ), do not appear to contribute to O157 adherence to squamous epithelial (RSE) cells constituting this primary site of O157 colonization in cattle
LEE- encoded proteins considered critical for O157 adherence to FAE cells at the RAJ did not appear to have a role in O157 adherence to RSE cells at this same site
Both O157 strains grown in Dulbecco Modified Eagle Medium-Low Glucose (DMEM) and pre-incubated with pooled, polyclonal antisera generated against the LEE (Tir, EspA, EspB, and Intimin) and flagellar H7 proteins, or the anti-Intimin antisera alone, at 1:5 and 1:10 dilution, continued to adhere to the RSE cells, irrespective of the presence/absence of D + Mannose

Summary

Introduction

We present evidence that proteins encoded by the Locus of Enterocyte Effacement (LEE), considered critical for Escherichia coli O157 (O157) adherence to follicle-associated epithelial (FAE) cells at the bovine recto-anal junction (RAJ), do not appear to contribute to O157 adherence to squamous epithelial (RSE) cells constituting this primary site of O157 colonization in cattle. Similar results were observed with another vaccine that targets the O157 siderophore receptor and porin (SRP) proteins [17,18]; https://animalhealth.pfizer.com This clearly suggests that unidentified proteins other than those constituting the TTSS or SRP may play a crucial role in bovine colonization, and that the identification and inclusion of such proteins is likely to increase the efficacy of vaccines for elimination of O157 from the gastrointestinal tracts of cattle. Further supporting this inference are reported observations that the TTSS proteins do not significantly contribute to the persistence of O157 in feedlot cattle [19], or to O157 invasion of crypt cells at the RAJ [20]

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