Prevalence of shigatoxigenic Escherichia coli in bovine cattle: a survey in the north region of portugal

Shiga toxin-producing Escherichia coli (STEC) strains are food-borne pathogens that can be transmitted to humans through many different routes, but mainly through consumption of contaminated foods. STEC strains are characterized by the production of Shiga toxins (Stx) that are encoded by two genes stx1 and/or stx2. Each toxin can be subdivided into subtypes and, currently, there are three known subtypes for stx1 (stx1a, stx1c, and stx1d) and seven for stx2 (stx2a, stx2b, stx2c, stx2d, stx2e, stx2f, and stx2g). Others virulence factors, such the production of intimin protein, encoded by eae gene, are associated with severe outcomes of STEC-associated diseases. The most common STEC serotype implicated worldwide is E. coli O157:H7, but many other STEC strains are associated with severe human diseases. Ruminants, especially cattle, are a major reservoir for O157 and non-O157 STEC. Information on STEC prevalence in Portuguese dairy cattle is limited, so we analysed for the presence of STEC 329 faecal specimens collected from the rectum of healthy dairy cattle. The samples were collected from adults lactating cows (n=194) and from heifers (n=135) with ages among 6 to 18 months, between March and June 2019, at milk farms (n=17) in the North region of Portugal. After enrichment, in modified TSB with novobiocin, samples were analysed by real time PCR to detect the presence of stx1, stx2 and eae in accordance to ISO/TS 13136:2012(E). In addition, conventional PCR for the detection of sxt1 and stx2 gene subtypes was performed according to the guidelines of the VTEC European Union Reference Laboratory. A total of 139 isolates were recovered from 108 positive animals (dairy cows and heifers). The STEC prevalence was significantly higher in heifers (68/135; 50.4%) than in adult cows (40/194; 20.6%) (p < 0.05, Fisher exact test statistic value is