Abstract
BackgroundIn the less-sensitive mouse model, Shiga toxin-producing Escherichia coli (STEC) challenges result in shedding that reflect the amount of infection and the expression of virulence factors such as Shiga toxins (Stx). The purpose of this study was to characterize the contribution of STEC diversity and Stx expression to shedding in beef feeder calves and to evaluate the effectiveness of a prebiotic, Celmanax®, to alleviate STEC shedding. Fecal samples were collected from calves at entry and after 35 days in the feedlot in spring and summer. STECs were evaluated using selective media, biochemical profile, serotyping and Stx detection. Statistical analysis was performed using repeated measures ANOVA and logistic regression.ResultsAt entry, non-O157 STEC were dominant in shedding calves. In spring, 21%, 14% and 14% of calves acquired O157, non-O157 and mixed STEC infections, respectively. In contrast, 45%, 48% and 46% of calves in summer acquired O157, non-O157 and mixed STEC infections, respectively. Treatment with a prebiotic, Celmanax®, in spring significantly reduced 50% of the O157 STEC infections, 50% of the non-O157 STEC infections and 36% of the STEC co-infections (P = 0.037). In summer, there was no significant effect of the prebiotic on STEC infections. The amount of shedding at entry was significantly related to the number and type of STECs present and Stx expression (r2 = 0.82). The same relationship was found for shedding at day 35 (r2 = 0.85), but it was also related to the number and type of STECs present at entry. Stx - producing STEC infections resulted in 100 to 1000 × higher shedding in calves compared with Stx-negative STECs.ConclusionsSTEC infections in beef feeder calves reflect the number and type of STECs involved in the infection and STEC expression of Stx. Application of Celmanax® reduced O157 and non-O157 STEC shedding by calves but further research is required to determine appropriate dosages to manage STEC infections.
Highlights
In the less-sensitive mouse model, Shiga toxin-producing Escherichia coli (STEC) challenges result in shedding that reflect the amount of infection and the expression of virulence factors such as Shiga toxins (Stx)
Stx is associated with STEC infection in challenge studies with immature calves [13,14,15] and Stx2 increases STEC colonization of enterocytes isolated from mature cattle in vitro [16] while, Stx1 is toxic to particular classes of lymphocytes in immature calves [15]
If we are to improve on current methods to reduce food safety concerns associated with STEC transmission to foods, it is essential that we examine STEC pathogenesis in older calves and mature cattle
Summary
In the less-sensitive mouse model, Shiga toxin-producing Escherichia coli (STEC) challenges result in shedding that reflect the amount of infection and the expression of virulence factors such as Shiga toxins (Stx). The purpose of this study was to characterize the contribution of STEC diversity and Stx expression to shedding in beef feeder calves and to evaluate the effectiveness of a prebiotic, CelmanaxW, to alleviate STEC shedding. The clinical symptoms described for STEC infections in beef feeder calves and mature cattle resemble those described in another less sensitive STEC disease model, the mouse, and include discolored feces, hind-limb paralysis, tremors, ataxia and death [8,9,10]. As antibiotics are contraindicated for STEC infections in humans [20] and prebiotic/probiotic applications alleviate the clinical symptoms and the development of acute STEC-associated disease in cattle [6,7], a similar approach could address food safety concerns. The second objective was to determine the impact of a prebiotic, CelmanaxW, application on STEC infections and shedding in beef feeder calves
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