Distribution of Shiga Toxin Genes in Shiga Toxin–Producing Escherichia coli from Healthy Livestock and Poultry in Tunisia: Zoonotic Risk and Association with Integrons

Shiga toxin–producing Escherichia coli produce Shiga toxins, the primary virulence factors responsible for severe gastroenteritis and, in some cases, hemolytic uremic syndrome. The objective of this study was to investigate host- and strain-associated factors influencing the distribution of stx genes by analyzing data from Shiga toxin–producing Escherichia coli strains isolated from fecal samples of healthy livestock and poultry in Tunisia. A total of 116 Shiga toxin–producing Escherichia coli isolates from cattle, camels, and chickens in Tunisia were analyzed for the distribution of stx genes in relation to serogroups, host species, phylogroups, and integron carriage. This analysis was carried out to identify the factors influencing stx gene frequency and to explore potential mechanisms involved in their dissemination among diverse Shiga toxin–producing Escherichia coli serotypes. Shiga toxin genes were detected in all 116 isolates, with stx1 and stx2 identified in 75% (87/116) and 32.8% (38/116) of isolates, respectively. Across the seven tested serogroups (O26, O45, O91, O103, O121, O145, and O157), stx1 was detected in all groups, whereas stx2 was most frequent in serogroup O145 and absent in O121 and O91. The prevalence of stx1 varied significantly by host (p = .002), with the highest proportion in chickens, followed by cattle, while stx2 was most prevalent in camels and secondarily in cattle (p = .001). A significantly higher prevalence of stx2 was observed in phylogroups E and Clade I compared to other phylogroups (p = .005). Furthermore, stx1 was significantly more common in integron-positive isolates than in integron-negative isolates (p = .003). Shiga toxin genes were frequently detected in high-risk serogroups (O103, O145, and O157), predominantly within pathogenic phylogroups B2 and E, indicating an increased zoonotic risk. The significant association between integrons and stx genes (p = .003) suggests the co-selection of virulence and antimicrobial resistance traits, which represents a potential public health risk in Tunisian food animals.

Cite this article as: Tayh, G., & Messadi, L. (2026). Distribution of shiga toxin genes in shiga toxin–producing Escherichia coli from healthy livestock and poultry in Tunisia: zoonotic risk and association with integrons. Acta Veterinaria Eurasia, 52, 0260, doi:10.5152/actavet.2026.25260.