Edinburgh Napier University

  Shiga-toxin producing E. coli (STEC) are zoonotic pathogens, which release phage-encoded Shiga toxins (Stx). Stx subtypes stx2a and stx2d are associated with severe human disease. STEC O157 is the most common serotype in human disease although other pathogenic serotypes exist. Cattle, sheep and deer can carry STEC. A recent study found STEC O157 prevalence of 0.34 % (95 % CI = 0.02 – 6.30) in Scottish wild deer; however 69.5 % of faecal samples were stx positive suggesting presence of pathogenic non-O157 STEC serotypes.

The aims of this project were: (i) to investigate prevalence and factors associated with carriage of stx2a genes in Scottish wild deer; (ii) to determine pathogenic potential of non-O157 STEC strains isolated from Scottish wild deer using whole genome sequencing (WGS).

PCR testing of faecal samples found 12 % of stx positive samples were subtype stx2a. In an ‘all deer species’ model, roe deer and sheep density had significant positive associations with stx2a. In a ‘roe deer only’ model, South of Scotland, % semi-natural grassland and rain-days in month had significant positive association with stx2a. WGS of 56 non-O157 STEC strains isolated from deer faeces identified five strains genetically similar to individual Scottish human clinical non-O157 STEC isolates. Of these, two deer isolates had identical stx and virulence gene profiles to the closest human isolates, and three strains differed only by one or two virulence genes, including a stx2d positive strain. The majority of isolates (47/56) had low pathogenic subtypes stx2b or stx2b:stx1c. Although stx2a was found in three isolates, none were genetically similar to human clinical strains.

In conclusion, this study found roe deer were more likely to carry pathogenic stx2a and presence of sheep and environmental factors may influence this. Non-O157 STEC strains from deer are likely to cause diarrhoea but not severe human disease.