Molecular Characterization of Shiga Toxin Genes (stx1 and stx2) in Escherichia coli O157:H7 Isolated from Beef in Lafia and Akwanga Metropolis, Nasarawa State, Nigeria

Background: Shiga toxin-producing Escherichia coli (STEC) O157:H7 is a major foodborne pathogen responsible for severe human illnesses, including haemorrhagic colitis and haemolytic uraemic syndrome (HUS). The primary virulence determinants are stx1 and stx2 genes. This study aimed to detect these virulence genes in E. coli O157:H7 isolated from beef sold in Lafia and Akwanga, Nasarawa State, Nigeria. Methods: Fifteen previously confirmed E. coli O157:H7 isolates (from 29 originally recovered from 300 beef samples) were selected from six locations (abattoirs and markets) in Lafia and Akwanga. Genomic DNA was extracted using the cetyltrimethylammonium bromide (CTAB) method. A multiplex PCR assay targeting stx1 (349 bp) and stx2 (110 bp) was performed using standard primers. Positive controls (stx1⁺stx2⁺ ATCC 43888) and negative controls (ATCC 25922) were included. Results: Of 15 isolates tested, 3 (20.0%) carried Shiga toxin genes. Specifically, one isolate (6.7%) harboured both stx1 and stx2; two isolates (13.3%) carried stx2 alone; and none carried stx1 alone. The stx1⁺stx2⁺ isolate originated from Lafia Old Market, while stx2-only isolates came from Lafia Abattoir and Akwanga New Market. The dual-carriage strain poses the highest risk of HUS (>25% in infected children). Conclusion: Virulent STEC O157:H7 strains, including a high-risk stx1⁺stx2⁺ isolate, are present in retail beef in Nasarawa State. These findings highlight an urgent need for enhanced molecular surveillance, improved abattoir hygiene, and public health interventions to reduce foodborne transmission risks.