Abstract

Background Enterotoxigenic Escherichia coli (ETEC) cause significant diarrheal morbidity and mortality in children of resource-limited regions, warranting development of effective vaccine strategies. Genetic diversity of the ETEC pathovar has impeded development of broadly protective vaccines centered on the classical canonical antigens, the colonization factors and heat-labile toxin. Two non-canonical ETEC antigens, the EtpA adhesin, and the EatA mucinase are immunogenic in humans and protective in animal models. To foster rational vaccine design that complements existing strategies, we examined the distribution and molecular conservation of these antigens in a diverse population of ETEC isolates. Methods Geographically diverse ETEC isolates (n = 1159) were interrogated by PCR, immunoblotting, and/or whole genome sequencing (n = 46) to examine antigen conservation. The most divergent proteins were purified and their core functions assessed in vitro. Results EatA and EtpA or their coding sequences were present in 57.0% and 51.5% of the ETEC isolates overall, respectively; and were globally dispersed without significant regional differences in antigen distribution. These antigens also exhibited >93% amino acid sequence identity with even the most divergent proteins retaining the core adhesin and mucinase activity assigned to the prototype molecules. Conclusions EtpA and EatA are well-conserved molecules in the ETEC pathovar, suggesting that they serve important roles in virulence and that they could be exploited for rational vaccine design. Author summary Enterotoxigenic Escherichia coli (ETEC) are a significant cause of childhood diarrhea in low-middle income countries for which there is currently no vaccine. ETEC vaccine approaches to date have focused on antigens known as colonization factors (CFs) and the pathovar-defining toxins. However, both antigenic diversity of CFs and the lack of characterized CF antigens in many strains has hindered deployment of broadly protective ETEC vaccines. Nevertheless, more recent studies have identified additional ETEC virulence molecules that could compliment canonical vaccine strategies. Here, we demonstrate that two proteins, the EtpA adhesin and EatA mucinase, are present in a diverse, global collection of isolates, and are among the most highly conserved ETEC pathovar-specific antigens to be identified, providing additional incentive to explore their utility in the rational design of broadly protective ETEC vaccines.