|Nisbet, David - Dave|
Submitted to: Microbial Ecology
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/2007
Publication Date: 11/28/2007
Citation: Edrington, T.S., Callaway, T.R., Nisbet, D.J. 2007. Research investigating the seasonal prevalence of E. coli O157:H7 in cattle [abstract]. In: Proceedings of II International Conference on Environmental, Industrial and Applied Microbiology, November 28-December 1, 2007, Seville, Spain. p. 53. Interpretive Summary:
Technical Abstract: In the United States, seasonal shedding of E. coli O157:H7 (EHEC) in ruminants is well documented and characterized by higher prevalence in the summer months decreasing to very low or undetectable levels in the winter. Reasons for this phenomenon are unknown and we hypothesize that seasonal shedding of EHEC is a result of physiological responses by the animal to changing day-length. Results from a series of experiments conducted to test this hypothesis are presented below. In the first experiment, we examined the influence of exogenous melatonin (MEL) on fecal shedding of EHEC in feedlot cattle. Animals were maintained on a feedlot ration and received via oral bolus one of two treatments: Control (empty capsule) or a capsule containing MEL (0.5 mg/kg BW; 1X) daily for 7 d. Following a 5-d period of no treatment, a second MEL dose (5.0 mg/kg BW; 10X) was administered daily for 4 d and cattle monitored an additional 9 d. No differences (P > 0.10) were observed in daily fecal shedding of EHEC in animals treated with the 1X dose for 9 d or during the subsequent 5 d. However, the 10X dose decreased (P = 0.05) the number of cattle shedding EHEC compared to control steers. Following cessation of treatments, shedding patterns were similar (P > 0.10). A second series of experiments evaluated the role of the thyroid hormones on fecal shedding of EHEC. Chemical inhibition of the thyroid via administration of propyl-thiouracil (PTU) had no effect on fecal shedding, although following termination of the PTU treatment, a greater percentage of PTU-treated animals shed EHEC compared to control steers. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of EHEC during the winter or exacerbate shedding in the summer. Treatment with exogenous T3 (1.5 mg T3 suspended in corn oil injected s.c daily) produced a significant change in serum thyroid hormone concentrations indicative of a hyperthyroid status in both experiments. No differences (P > 0.10) were observed in fecal shedding of EHEC in the winter experiment but in the summer experiment, fecal shedding was decreased (P = 0.05) by administration of T3. To examine the effect of artificial lighting on EHEC prevalence, four pens of feedlot cattle received approximately 5 h of artificial lighting, commencing prior to sunset, daily for 60 days and four pens served as unlighted controls. The experiment was conducted in the early fall when day-length and fecal prevalence of EHEC was decreasing. Fecal samples were collected after 25 and 53 days of artificial lighting and 28 and 43 days following cessation of the lighting treatment. Fecal prevalence of EHEC remained constant in the lighted pens whereas a decrease (P < 0.01) was observed in the control treatment after 53 days of lighting. Forty-three days following cessation of the lighting treatment, prevalence decreased in the lighted treatment to levels comparable (P > 0.20) to control levels. Results indicate that hormones known to respond to changing day-length may play a role in the seasonal shedding of EHEC in ruminants. Understanding the mechanisms underlying the seasonality of this pathogen will enable the implementation of effective control strategies when it is most prevalent.