Directed Evaluation of Enterotoxigenic Escherichia coli Autotransporter Proteins as Putative Vaccine Candidates

Jessica A Harris,Rita Kansal,Koushik Roy,James M Fleckenstein,David J Hamilton,Virginia Woo-Rasberry,Firdausi Qadri,Elizabeth Angelica Leme Martins

doi:10.1371/journal.pntd.0001428

Abstract

BackgroundEnterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in developing countries, where it accounts for millions of infections and hundreds of thousands of deaths annually. While vaccine development to prevent diarrheal illness due to ETEC is feasible, extensive effort is needed to identify conserved antigenic targets. Pathogenic Escherichia coli, including ETEC, use the autotransporter (AT) secretion mechanism to export virulence factors. AT proteins are comprised of a highly conserved carboxy terminal outer membrane beta barrel and a surface-exposed amino terminal passenger domain. Recent immunoproteomic studies suggesting that multiple autotransporter passenger domains are recognized during ETEC infection prompted the present studies.MethodologyAvailable ETEC genomes were examined to identify AT coding sequences present in pathogenic isolates, but not in the commensal E. coli HS strain. Passenger domains of the corresponding autotransporters were cloned and expressed as recombinant antigens, and the immune response to these proteins was then examined using convalescent sera from patients and experimentally infected mice.Principal FindingsPotential AT genes shared by ETEC strains, but absent in the E. coli commensal HS strain were identified. Recombinant passenger domains derived from autotransporters, including Ag43 and an AT designated pAT, were recognized by antibodies from mice following intestinal challenge with H10407, and both Ag43 and pAT were identified on the surface of ETEC by flow cytometry. Likewise, convalescent sera from patients with ETEC diarrhea recognized Ag43 and pAT, suggesting that these proteins are expressed during both experimental and naturally occurring ETEC infections and that they are immunogenic. Vaccination of mice with recombinant passenger domains from either pAT or Ag43 afforded protection against intestinal colonization with ETEC.ConclusionsPassenger domains of conserved autotransporter proteins could contribute to protective immune responses that develop following infection with ETEC, and these antigens consequently represent potential targets to explore in vaccine development.

Highlights

Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal illness in developing countries where these organisms cause hundreds of millions of infections and an estimated 300,000– 500,000 deaths in young children each year [1]
Passenger domains of conserved autotransporter proteins could contribute to protective immune responses that develop following infection with ETEC, and these antigens represent potential targets to explore in vaccine development
The resulting sequences containing these domains were used to identify additional autotransporters in the genome of ETEC strain H10407 available in un-annotated form via the Sanger Institute, which was facilitated by interrogating the available sequence using the National Microbial Pathogen Database Resource (NMPDR) [30] on the Rapid Annotation Subsystem Technology (RAST) server [31]

Summary

Introduction

Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal illness in developing countries where these organisms cause hundreds of millions of infections and an estimated 300,000– 500,000 deaths in young children each year [1]. A variety of more than 25 antigenically distinct fimbrial, or fibrillar CFs have been described to date [5,6] These antigens, along with LT, remain central to ETEC vaccine development [7]. CF antigens are not appreciably cross-protective, and Conserved ETEC Autotransporter Passenger Vaccines. Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in developing countries, where it accounts for millions of infections and hundreds of thousands of deaths annually. While vaccine development to prevent diarrheal illness due to ETEC is feasible, extensive effort is needed to identify conserved antigenic targets. Recent immunoproteomic studies suggesting that multiple autotransporter passenger domains are recognized during ETEC infection prompted the present studies

Methods

Results

Discussion

Conclusion