Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 8, 2006
Publication Date: March 30, 2007
Citation: Edrington, T.S., Callaway, T.R., Hallford, D.M., Anderson, R.C., Nisbet, D.J. 2007. Influence of exogenous triiodothyronine (T3) on fecal shedding of Escherichia coli O157 in cattle. Microbial Ecology. 53:664-669. Interpretive Summary: Some cattle and sheep are naturally infected with E. coli O157:H7, a bacteria that causes food sickness in humans. This bacteria is more common in cattle in the summer months than in the winter but nobody knows the reason for this seasonality. We believe that changing day-length and the animal’s response to this change are the reasons for seasonal prevalence of E. coli O157:H7. The thyroid is one gland that responds to changing day-length. We administered a hormone produced by the thyroid to cattle to determine it’s role in fecal shedding of E. coli O157:H7 in the winter and summer. The thyroid hormone treatment had no affect on fecal shedding of E. coli O157:H7 in the winter, but did decrease the incidence in the summer compared to untreated controls. Understanding the biology of E. coli O157:H7 will enable the design of effective strategies to control this bacteria when it is most common.
Technical Abstract: Fecal prevalence of E. coli O157 in ruminants is highest in the summer months and decreases to low or undetectable levels in the winter. We hypothesize that the seasonal variation of this pathogen is a result of physiological responses within the host animal to changing day-length. The thyroid is one gland known to respond to changing day-length. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of E. coli O157 in cattle during the winter when shedding is virtually non-existent (Winter experiment) or influence cattle actively shedding E. coli O157 (Summer experiment). Yearling cattle were group-penned under dry-lot conditions, adjusted to a high concentrate ration, and randomly assigned to treatment: Control (1 ml corn oil injected s.c. daily) or T3 (1.5 mg T3 suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T3 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 E. coli O157 in the winter experiment. In the summer experiment, fecal shedding of E. coli O157 was decreased (P = 0.05) by administration of T3 during the treatment period (d 1 to 10), tended to be lower (P = 0.08) during the following 7-d period of no treatment and was lower (P = 0.01) when examined across the entire experimental period. Results of this research indicate that the thyroid or its hormones may be involved in the seasonal shedding patterns of E. coli O157 in cattle.