Comparison of Challenge Models for Determining the Colonization Dose of Campylobacter jejuni in Broiler Chicks

Authors: Line, John; Hiett, Kelli

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2008
Publication Date: 9/1/2008
Citation: Line, J.E., Hiett, K.L. 2008. Comparison of Challenge Models for Determining the Colonization Dose of Campylobacter jejuni in Broiler Chicks. Poultry Science. 87:1700-1706.

Interpretive Summary: Coprophagia (the oral ingestion of fecal matter) is a normal activity of broiler chickens. The spread of poultry disease-causing and human food-borne pathogens through the fecal-oral route is well documented. Campylobacter jejuni is a human food-borne pathogen of primary importance. Poultry are frequently contaminated with C. jejuni during production with the majority of commercial U.S. flocks positive for the organism by the time the birds reach market age at about 6 weeks. A number of investigations have been conducted in an effort to reduce populations of foodborne pathogens in poultry on the farm so that lesser populations of pathogens enter the processing facility and subsequent consumer exposure is diminished. Studies to determine the population of a specific pathogen necessary to colonize 50% of experimental animals inoculated (colonization dose 50% or CD50) can be misled by subsequent coprophagous activity among animals. The purpose of these experiments was to determine the effect of coprophagia on estimates of the CD50 for C. jejuni RM1221 in broiler chicks. C. jejuni RM1221 was orally administered in measured doses to newly hatched chicks. The chicks were housed either individually in cages not allowing coprophagic activity, or in isolation units containing groups of birds where coprophagia was allowed. The birds were sacrificed and analyzed for Campylobacter in the ceca on day 7 post-inoculation. The CD50 was calculated and results from the two models were compared. Elimination of coprophagia as an uncontrolled variable led to a more clear determination of the estimated CD50 of about 316 CFU C. jejuni RM1221 as demonstrated in the individually-housed chick model. Coprophagous activity obscured results in the chicken experimental model where it is not prevented. The individual bird challenge model is superior to the group challenge model for trials designed to determine colonization dose and would be recommended to researchers in industry, academia and government who conduct such studies.

Technical Abstract: Coprophagous activity is normal among broiler chickens. The purpose of these experiments was to determine the effect of coprophagia on estimates of the population of Campylobacter jejuni RM1221 necessary to colonize 50% of broiler chicks inoculated (colonization dose 50% or CD50). Campylobacter jejuni RM1221 was sequentially passaged in the laboratory 128 times and was then orally administered in measured doses to newly hatched chicks. The chicks were housed either individually in cages not allowing coprophagous activity, or in isolation units containing groups of birds where coprophagia was allowed. The birds were sacrificed and analyzed for Campylobacter in the ceca on day 7 post-inoculation. The CD50 was calculated and results from the two models were compared. Elimination of coprophagia as an uncontrolled variable led to a more clear determination of the estimated CD50 of about 316 CFU C. jejuni RM1221 as demonstrated in the individually-housed chick model. This study demonstrated that estimates of the CD50 can be misled by coprophagous activity among chickens which may obscure results in any experimental model where it is not prevented. The individual bird challenge model is superior to the group challenge model for trials designed to determine colonization dose.