Campylobacter colonization in broilers

Abstract

Poultry is generally considered the most important source of foodborne campylobacteriosis. Field studies have provided knowledge on risk factors for colonization of commercial broilers, but the exact routes of transmission remain largely unknown. To identify these routes and develop specific interventions, information on the moment of introduction would be useful. Therefore, in this thesis transmission of Campylobacter among broilers was studied in experimentally exposed groups of broilers and in commercial broiler flocks. In the commercial flocks the moment that the first bird in a flock was colonized was estimated with a accuracy of three days. Because reduction of the susceptibility of broilers could help to reduce the incidence of positive broiler flocks, the effect of feed supplementation with Medium Chain Fatty Acids on susceptibility was studied in broilers. The dose response curve of broilers that were provided MCFA supplemented feed was shifted to the right, indicating that they required higher inoculation doses to become colonized than non-supplemented broilers. MCFA feed supplementation might therefore be a helpful tool for the reduction of susceptibility in broilers. If eventually flock colonization cannot be prevented, interventions that reduce colonization levels in the digestive tract at slaughtering might reduce carcass contamination levels and subsequently human exposure. Both the upper part of the digestive tract, in particular the crop, and the intestines might cause cross-contamination of the carcass at evisceration. Therefore, the effect of drinking water supplementation with volatile fatty acids (VFA) on Campylobacter levels was assessed in crop and ceca of Campylobacter-colonized broilers. VFA supplementation did not reduce colonization levels neither in the crop nor in the ceca, and no correlation between crop and cecal Campylobacter levels was detected. Colonization properties of Campylobacter are usually studied in chickens. Alternatively, a colonization model in chicken embryos might resemble the micro-environmental conditions in young chickens, and might allow for the evaluation of Campylobacter colonization potential and bacterium-host interaction in absence of gut flora. Therefore, intestinal colonization characteristics of embryonated chicken eggs at 16 days of incubation were studied. The observed colonization levels suggested that the embryo model provides conditions favoring a steady growth of Campylobacter and the estimated analytical sensitivity indicated that the embryo model is a sensitive tool for the detection of Campylobacter. Various methods and models have been used, evaluated and improved in this thesis. Depending on the aim of future studies on pathogenesis or the aim of control measures that are developed, these methods and models could prove useful.