Live attenuated vaccine-based control of necrotic enteritis of broiler chickens》.pdfVIP

Veterinary Microbiology 113 (2006) 25–34 /locate/vetmic Live attenuated vaccine-based control of necrotic enteritis of broiler chickens D.R. Thompson, V.R. Parreira, R.R. Kulkarni, J.F. Prescott * Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ont., Canada N1G 2W1 Received 19 May 2005; received in revised form 21 September 2005; accepted 3 October 2005 Abstract A vaccine for necrotic enteritis (NE) of chickens would reduce the current need to prevent or treat the disease in broiler chickens with antimicrobial drugs. The objective of this study was to understand aspects of immunity to the disease. The first experiment examined the virulence of six strains of Clostridium perfringens isolated from cases of NE in broiler chickens. Using a 5-day experimental oral infection of 2-week-old broiler chickens, four of the six strains were found to be virulent. Pulsed-field gel electrophoresis and PCR showed that virulence was not associated with a plasmid encoding the beta2 toxin gene, cpb2, since this was present in virulent and one of the two avirulent strains. In the second experiment, two virulent and one avirulent strains were tested for their ability to immunize (‘‘infection- immunization’’) chickens through the oral route. The procedure used experimental infection for 5 days followed by bacitracin treatment for 9 days, and then re-challenge 2 days later with a virulent strain, CP4. Infection-immunization with the virulent isolates protected chickens from subsequent virulent challenge, whereas the infection-immunization with the avirulent isolate did not. In a third experiment, two of four alpha-toxin-negative mutants of CP4 protected