Heat stress, Eimeria spp. and C. perfringens infections alone or in combination modify gut Th1/Th2 cytokine balance and avian necrotic enteritis pathogenesis.

Information on the dynamics of the chicken immune system during bacterial or parasite challenge in the presence or absence of stressful situations may provide a better understanding of the complex mechanisms behind these diseases. Necrotic enteritis (NE) had been controlled previously by the proper use of antimicrobial agents; however, more recently, NE has reemerged in many countries. The imposed restrictions on antimicrobial use and/or the intensive productive programs implemented by producers are challenges the birds, leading to large host adaptive responses that in many instances are like those elicited by stressors. This study analyses the effects of heat stress on Th1/Th2 cytokine balance, pathological features, and Toll-like receptor expression in the small intestine of broiler chickens infected with Clostridium perfringens type A in the presence or absence of Eimeria spp. co-infection. This co-infection model was experimentally used because it reproduces the findings commonly observed in the field during avian NE. For this purpose, broiler chickens infected with C. perfringens and/or Eimeria spp. were reared in isolator chambers subjected or not to heat stress intermittently. It was observed that heat stress directs the expression of Th2-type cytokines, increases Toll-like receptor 4 expression in the intestine and reduces the disease severity induced by Eimeria spp. and C. perfringens infections alone or in combination, most likely as a consequence of stress-induced changes in brain-gut axis activity.

Effects of long-term heat stress in an experimental model of avian necrotic enteritis.

Stressful conditions are predisposing factors for disease development. Heat stress is one of the most important stressors in poultry production. The reemergence of some previously controlled diseases [e.g., avian necrotic enteritis (NE)] has been extensively reported. The combination of bacterial infection and certain environmental factors have been reported to trigger the disease. The aim of this study was to analyze the effects of long-term heat stress (35 ± 1°C) on the development of NE in broiler chickens. For this purpose, 60 male broiler chickens were divided into the following 6 groups: control group (C), heat stressed control group (C/HS35), thioglycolate group (T), thioglycolate heat-stressed group (T/HS35), infected group (I), and infected heat-stressed group (I/HS35). The poultry of groups I and I/HS35 were experimentally infected with Clostridium perfringens via their feed from 15 to 21 d of life. Heat stress (35 ± 1°C) was constantly applied to the birds of the stressed groups from 14 to 21 d of life. The infected and heat-stressed broiler chickens presented a trend toward a decrease in gross lesion scores and significantly lower microscopic scores of necrosis in the duodenum and jejunum (P < 0.05), lower fusion of villi in the duodenum (P < 0.05), and lower congestion scores in the jejunum and ileum (P < 0.05) in relation to infected and non-heat-stressed chickens. Broilers of I/HS35 group also exhibited small number of heterophils in the duodenum and jejunum compared with those of the I group (P < 0.05). Furthermore, the duodenum and jejunum of infected and heat-stressed broilers showed lower number of clostridia on the intestinal mucosa (P < 0.05). Data were discussed in light of a heat stress induced reduction on intestinal inflammation via a decrease in heterophil migration to the intestinal mucosa, which in turn might have reduced tissue damage during inflammation, hence preventing the development of a more severe form of NE.

Production and release of heat-labile toxin by wild-type human-derived enterotoxigenic Escherichia coli.

Production and release of heat-labile toxin (LT) by wild-type enterotoxigenic Escherichia coli (ETEC) strains, isolated from diarrheic and asymptomatic Brazilian children, was studied under in vitro and in vivo conditions. Based on a set of 26 genetically diverse LT(+) enterotoxigenic E. coli strains, cell-bound LT concentrations varied from 49.8 to 2415 ng mL(-1). The amounts of toxin released in culture supernatants ranged from 0% to 50% of the total synthesized toxin. The amount of LT associated with secreted membrane vesicles represented <5% of the total toxin detected in culture supernatants. ETEC strains secreting higher amounts of LT, but not those producing high intracellular levels of cell-bound toxin, elicited enhanced fluid accumulation in tied rabbit ileal loops, suggesting that the strain-specific differences in production and secretion of LT correlates with symptoms induced in vivo. However, no clear correlation was established between the ability to produce and secrete LT and the clinical symptoms of the infected individuals. The present results indicate that production and release of LT by wild-type human-derived ETEC strains are heterogeneous traits under both in vitro and in vivo growth conditions and may impact the clinical outcomes of infected individuals.

Cell-detaching Escherichia coli (CDEC) strains from children with diarrhea: Identification of a protein with toxigenic activity.

Twenty-four strains of cell-detaching Escherichia coli (CDEC) isolated from stool specimens in different cities in Brazil were examined for virulence properties. Aerobactin production and multiple antibiotic resistance were observed in most of the isolates. In hybridization studies, the alphahly, pap, and cnf sequences, common properties of this category of E. coli, were found in a minority of isolates. Half of the CDEC isolates had enteroaggregative DNA sequences (pet, astA, aggA), six strains carried the shet1 gene, nine strains carried the daaC sequence, and one strain carried the stp gene. Thirteen strains induced fluid accumulation in the rabbit intestinal loop assay. Supernatant filtrate of one of those strains, which did not hybridize with any of the toxin probes tested, induced destructive lesions in the rabbit ileal loop and enterotoxic activity in the Ussing chamber. A 12-kDa protein purified by 60% ammonium sulfate precipitation of the supernatant filtrate demonstrated a toxigenic effect that was inhibited by the anti-12-kDa protein antiserum.