The neuroendocrine stress hormone norepinephrine augments Escherichia coli O157:H7-induced enteritis and adherence in a bovine ligated ileal loop model of infection

Abstract

The role of the neuroendocrine environment in the pathogenesis of enteric bacterial infections is increasingly being recognized. Here we report that norepinephrine augments Escherichia coli O157:H7-induced intestinal inflammatory and secretory responses as well as bacterial adherence to intestinal mucosa in a bovine ligated ileal loop model of infection. Norepinephrine modulation of enteritis and adherence was dependent on the ability of E. coli O157:H7 to form attaching and effacing lesions.

FIG. 1.

Effect of NE on intestinal secretory and inflammatory responses induced by E. coli strains 85-170 Nal^r and 85-170 Nal^r Δeae Δtir in the mid-ileum of 35- to 38-day-old calves. (A) Fluid accumulation. The ratio of the volume of fluid accumulated to loop length (V/L) for each treatment was determined from triplicate determinations in each calf. The values shown represent the means (± standard errors of the means) of the results for each treatment from four independent experiments. (B) Neutrophil infiltration. Total ¹¹¹In activity in the contents and mucosa was corrected for loop length and expressed as a ratio of the total activity in loops containing 85-170 Nal^r plus diluent. The mean value for each treatment in a single animal was determined, and then the mean neutrophil influx (± standard error of the mean) of the results from the four independent experiments was calculated.

FIG. 2.

Light micrographs of hematoxylin and eosin-stained bovine mid-ileal mucosa from ligated loops inoculated with E. coli O157:H7 strain 85-170 Nal^r in the presence of diluent (A) or 5 mM NE (B). Magnification, ×250.

FIG. 3.

Confocal laser scanning micrographs of bovine mid-ileal mucosa from ligated loops inoculated with E. coli O157:H7 strain 85-170 Nal^r in the presence of diluent (A) or 5 mM NE (B). F-actin was stained with fluorescein isothiocyanate-conjugated phalloidin (green), and bacteria were detected with rabbit anti-O157 typing serum and anti-rabbit immunoglobulin Alexa 568 (red) as described previously (40). Dense MC of intimately attached bacteria were seen only in the presence of NE. Magnification, ×630. (C) Semiquantitative analysis of bacterial adherence. The percentage of intact villi exhibiting MC of >5 adherent bacteria was calculated from four nonconsecutive sections from a single loop in each animal, and the means (± standard errors of the means) were then determined for the four animals used. At least 50 villi were examined in each nonconsecutive section.

FIG. 4.

Transmission electron micrographs of bovine mid-ileal mucosa showing A/E lesions induced by E. coli O157:H7 in the presence of 5 mM NE. Fixation, staining, and image capture were performed as described previously (41). Scale bars, 10 μm (A) and 5 μm (B).