# Prevalence of selected Shiga toxin-producing Escherichia coli vaccine antigen genes among two geographically distinct ruminant populations

## TL;DR

This study examines how common certain STEC vaccine antigens are in ruminant populations in California and Ireland to assess their potential for a human vaccine.

## Contribution

The study identifies three STEC antigen genes that are highly prevalent in geographically distinct ruminant populations, supporting their potential as vaccine candidates.

## Key findings

- Four antigen genes were highly prevalent in STEC isolates from a Californian dairy herd.
- Three of these genes were also highly prevalent in Irish cattle fecal samples.
- Discrepancies in terD gene prevalence were likely due to differences in isolation media.

## Abstract

Introduction. Shiga toxin-producing Escherichia coli (STEC) are a group of bacteria that cause severe bloody diarrhoea and haemolytic uraemic syndrome and are associated with neurological complications and potentially life-threatening infections. Children under five and elderly individuals are particularly vulnerable to STEC infections. The majority of STEC infections have been traced back directly or indirectly to ruminants, and there is an unmet need for a vaccine to protect these vulnerable cohorts.

Gap Statement. We previously identified a series of STEC proteins that are involved in attachment to human gastrointestinal epithelial cells, some of which are protective in a murine challenge model. However, the prevalence of the genes in dairy herds was unknown.

Aim. Due to zoonotic transmission, the development of a successful human vaccine relies on any protective vaccine antigens being prevalent in ruminant herds in different geographical locations. We aimed to examine the potential geographical differences in antigen gene prevalence.

Methodology. Faecal isolates collected from a dairy herd in CA, USA, and isolated from dairy cows in Ireland were analysed by quantitative PCR. Bioinformatic analysis of previously sequenced isolates was also performed.

Results. Four antigen genes were highly prevalent among STEC shed from cattle in a Californian dairy herd (>95.7%). Genes encoding FkpA, YiaF and GlnH were also highly prevalent in faecal samples from cows sampled in Ireland (93%). The point prevalence of terD among cattle in the Irish cohort appeared low relative to Californian isolates, but this is most likely due to the absence of tellurite in isolation media used in the former. Expansion of the study to examine Irish bovine and ovine Whole genome sequencing datasets increased the detection of terD in Irish isolates.

Conclusion. Overall, three antigen genes are prevalent in both geographically distinct cohorts. Discrepancies in terD gene prevalence are likely due to the use of selective agars in isolation protocols.