Shiga toxin-producing Escherichia coli in food and their pathogenic potential for humans

Abstract Background Shiga toxin-producing Escherichia coli (STEC) can cause diseases in humans ranging from mild diarrhoea to haemolytic uremic syndrome (HUS), due to Shiga-toxin production. The ingestion of contaminated food is the main route of transmission of STEC to humans. According to EFSA, STEC is the fourth cause of foodborne illness in the EU, with serious consequences in terms of human lives and healthcare costs. This study aimed to characterize STEC strains isolated from food, to inspect their virulence and antimicrobial resistance (AMR), providing an overview of the distribution and characteristics of STEC in food. Methods STEC detection was performed in different food matrices collected in Northern Italy (2018-2024), according to ISO/TS 13136:2012. Positive samples were identified using a Real-time PCR targeting stx1, stx2, and eae genes, encoding Shiga toxins and intimin, respectively. The whole genome of the STEC strains isolated from the positive samples was sequenced on an Illumina platform; serogroups, virulence genes, and AMR genes were then identified. Results A total of 82 STEC strains were isolated from cheese, milk, and meat; among them, 40% carried the stx2 gene and 15% also harboured the eae gene, associated with severe symptoms and HUS. Interestingly, 28 different serogroups were identified; 14% of the strains belonged to serogroups often involved in paediatric HUS and outbreaks (O26 and O103), whereas 15% of the isolates belonged to serogroups globally recognized as emerging (O80, O113, O128). Overall, 51.2% of the strains carried AMR genes, conferring resistance to β-lactams (n = 29, 35.4%), streptomycin and kanamycin (n = 21, 25.6%), and tetracycline (n = 17, 20.7%). Conclusions Our data suggested the circulation of genetically diverse STEC strains in food production environment, highlighting the importance of assessing STEC pathogenic potential for humans to support Competent Authorities in developing effective control, monitoring and prevention strategies. Key messages • The genetic diversity observed in STEC isolated from food highlights the importance of continuous monitoring to better assess the potential impact of the emerging strains on human public health. • From a One Health perspective, STEC surveillance is essential for preventing STEC infections and ensuring food safety.