Effect of the thyroid on faecal shedding of E. coli O157:H7 and Escherichia coli in naturally infected yearling beef cattle

Role of postnatal acquisition of the intestinal microbiome in the early development of immune function

OBJECTIVES

Therapy with broad-spectrum antibiotics is a common practice for premature infants. This treatment can reduce the biodiversity of the fecal microbiota and may be a factor in the cause of necrotizing enterocolitis. In contrast, probiotic treatment of premature infants reduces the incidence of necrotizing enterocolitis. We hypothesized that 1 mechanism for these observations is the influence of bacteria on postnatal development of the mucosal immune system.

MATERIALS AND METHODS

Expression of immune molecules and microbial sensors was investigated in the postnatal mouse gastrointestinal tract by real-time polymerase chain reaction. Subsequently, 2-week-old specific pathogen-free and microbial-reduced (MR; antibiotic treated) mice were compared for immune molecule and microbial sensor expression, mesenteric lymph node T-cell numbers and activation, intestinal barrier function/permeability, systemic lymphocyte numbers, and T-cell phenotype commitment.

RESULTS

Toll-like receptor 2, 4, and 5 expression was highest in 2-week-old specific pathogen-free mice, and this expression was decreased in MR mice. There was no difference in intestinal tight-junctional function, as evaluated by fluorescein isothiocyanate-dextran uptake, but MR mice had increased bacterial translocation across the intestinal epithelial barrier. MR mice had significantly fewer splenic B cells and mesenteric lymph node CD4+ T cells, but there were normal numbers of splenic T cells. These systemic T cells from MR mice produced more interleukin-4 and less interferon-gamma and IL-17, indicative of maintenance of the fetal, T-helper cell type 2 phenotype.

CONCLUSIONS

The present study shows that intestinal commensal microbiota have an influence on early postnatal immune development. Determining specific bacteria and/or bacterial ligands critical for this development could provide insight into the mechanisms by which broad-spectrum antibiotics and/or probiotic therapy influence the development of the mucosal immune system and mucosal-related diseases.

Escherichia coli O157:H7: recent advances in research on occurrence, transmission, and control in cattle and the production environment

Escherichia coli O157:H7 is a zoonotic pathogen that is an important cause of human foodborne and waterborne disease, with a spectrum of illnesses ranging from asymptomatic carriage and diarrhea to the sometimes fatal hemolytic uremic syndrome. Outbreaks of E. coli O157:H7 disease are often associated with undercooked beef, but there are other sources of transmission, including water, produce, and animal contact, which can often be linked directly or indirectly to cattle. Thus, preharvest control of this pathogen in cattle production should have a large impact on reducing the risk of human foodborne illness. In this review, we will summarize preharvest research on E. coli O157:H7 in cattle and the production environment, focusing on factors that may influence the transmission, prevalence, and levels of this pathogen, such as season, diet, high-level shedders, and animal stress. In addition, we will discuss recent research on the reduction of this pathogen in cattle production, including vaccination, probiotics, bacteriophage, and manure treatments.

Influence of exogenous triiodothyronine (T3) on fecal shedding of Escherichia coli O157 in cattle

Fecal prevalence of Escherichia 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 an endocrine 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 nonexistent (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 triiodothyronine (T(3); 1.5 mg suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T(3) 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 T(3) during the treatment period (days 1-10), tended to be lower (P=0.08) during the following 7-day 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.