Protection of chickens against Escherichia coli infections by DNA containing CpG motifs

Synthetic oligodeoxynucleotides (ODN) containing CpG motifs (CpG-ODN) have been shown to be effective immunoprotective agents in murine models for a variety of viral, intracellular bacterial, and protozoan infections. Until now, the use of CpG-ODN to protect against extracellular bacterial infections has not been reported. The objective of this study was to investigate the effect of CpG-ODN against cellulitis and colibacillosis in broiler chickens, using a well-established model. At 22 days of age, birds received CpG-ODN by either the subcutaneous or intramuscular route. Three days later, a virulent isolate of Escherichia coli was applied to a scratch site on the caudal abdominal skin. Birds were examined for 10 days after the E. coli challenge, and pathological and bacteriological assessments were conducted on all birds. The control group of birds receiving no CpG-ODN(2007) had a survival rate of 15%. In contrast, groups that received CpG-ODN(2007) by either subcutaneous or intramuscular injection, had significantly higher survival rates (P < 0.0001). Furthermore, the size of the cellulitis lesion was significantly smaller in groups that received CpG-ODN(2007) by the subcutaneous route (P < 0.01). A dose of as little as 3.16 mug of CpG-ODN(2007), delivered 3 days prior to challenge by either the subcutaneous or intramuscular route, significantly protected birds against E. coli infection (P < 0.01). This study demonstrates that CpG-ODN(2007) has both local and systemic protective effects in broiler chickens. This is the first time that CpG-ODN(2007) has been demonstrated to have an immunoprotective effect against an extracellular bacterial infection in any food animal species.