Effect of dexamethasone on bactericidal activity of turkey monocytes and implications for food safety

Authors: Huff, Geraldine; Huff, William; Rath, Narayan

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2015
Publication Date: 8/1/2015
Citation: Huff, G.R., Huff, W.E., Rath, N.C. 2015. Effect of dexamethasone on bactericidal activity of turkey monocytes and implications for food safety. Veterinary Immunology and Immunopathology. 166:151-158.

Interpretive Summary: Stress has been shown to affect the immune system of turkeys making them more susceptible to bacterial infections that may compromise food safety. Female turkeys are more resistant to stress-induced bacterial infections than are male turkeys. In order to determine the mechanism of this resistance, 5-week-old male and female turkeys were treated with a compound that mimics exposure to severe stress. Blood samples were taken to determine effects on the numbers of different types of white blood cells after stress. Samples of blood were also prepared and placed on glass slides. The blood cells that attached to the slides were challenged with bacteria to see if stress affected their ability to kill the bacteria. Treatment with the compound resulted in decreased ability to kill bacteria in all birds. The uptake of bacteria was increased in males and the cells from females were better at killing the internalized bacteria. Females had higher numbers of white blood cells that kill bacteria but there was no difference in the isolation of bacteria from the blood and tissues of challenged male and female turkeys. These results suggest that stress can decrease the ability of turkey blood cells to kill bacteria and can increase bacterial presence in blood and tissues, potentially affecting food safety.

Technical Abstract: Stress has been shown to affect the immune system of turkeys making them more susceptible to bacterial infections that may compromise food safety. Female turkeys are more resistant to stress-induced opportunistic bacterial infections than are male turkeys. In order to determine the mechanism of this resistance, 5-week-old male and female turkeys were treated with 3 intra-muscular injections of Dexamethasone (Dex) at 0, 0.5 and 2.0 mg/kg body weight on alternate days. Twenty-four hours after the third injection birds were bled and white blood cell (WBC) differentials of individual birds were determined. Pooled samples of glass-adherent mononuclear cells were cultured, challenged with Escherichia coli, and stained. The anti-bacterial activity of monocytes was measured by monitoring the percentage of infected cells over time. Dexamethasone at both 0.5 and 2.0 mg/kg significantly (P ' 0.05) decreased phagocytic activity in females only. Bacterial killing was significantly decreased at both concentrations of Dex at 8 and 16 hours post-infection in both sexes and was significantly lower in males as compared to females. Total WBC counts were significantly increased in females at both concentrations of Dex whereas male total WBC counts were unaffected. Both males and females had a significant increase in the heterophil to lymphocyte ratio. Within the same study, replicate pens of turkeys were challenged with intra-air sac inoculation of 100 cfu of E. coli. Isolation of the challenge strain of E. coli was significantly increased by both Dex and E. coli challenge, but there were no differences between sexes. These results suggest that stress can compromise bactericidal activity of turkey monocytes and increase bacterial colonization of blood and tissues, potentially affecting food safety. There were sex-related differences in the stress response of turkeys that may affect adherent monocyte bactericidal function, however at 5 weeks of age there was no evidence of gender effect on E. coli colonization.