Longitudinal molecular epidemiological study of thermophilic campylobacters on one conventional broiler chicken farm

Abstract

Improved understanding of the ecology and epidemiology of Campylobacter in the poultry farm environment is key to developing appropriate farm-based strategies for preventing flock colonization. The sources of Campylobacter causing broiler flock colonization were investigated on one poultry farm and its environment, from which samples were obtained on three occasions during each of 15 crop cycles. The farm was adjacent to a dairy farm, with which there was a shared concreted area and secondary entrance. There was considerable variation in the Campylobacter status of flocks at the various sampling times, at median ages of 20, 26, and 35 days, with 3 of the 15 flocks remaining negative at slaughter. Campylobacters were recoverable from various locations around the farm, even while the flock was Campylobacter negative, but the degree of environmental contamination increased substantially once the flock was positive. Molecular typing showed that strains from house surroundings and the dairy farm were similar to those subsequently detected in the flock and that several strains intermittently persisted through multiple crop cycles. The longitudinal nature of the study suggested that bovine fecal Campylobacter strains, initially recovered from the dairy yard, may subsequently colonize poultry. One such strain, despite being repeatedly recovered from the dairy areas, failed to colonize the concomitant flock during later crop cycles. The possibility of host adaptation of this strain was investigated with 16-day-old chickens experimentally exposed to this strain naturally present in, or spiked into, bovine feces. Although the birds became colonized by this infection model, the strain may preferentially infect cattle. The presence of Campylobacter genotypes in the external environment of the poultry farm, prior to their detection in broiler chickens, confirms the horizontal transmission of these bacteria into the flock and highlights the risk from multispecies farms.

FIG. 1.

Relationship between season and Campylobacter prevalence in different sample categories at the visit level.

FIG. 2.

Dendrogram derived from SmaI PFGE patterns showing matches to flock genotypes detected in environmental samples from crops 2 and 6 prior to detectable colonization. The band position tolerance was set at 1.4%, and clustering was performed using UPGMA. The scale indicates the percentage of similarity as determined with the Pearson coefficient. Isolate references comprise crop number, day of sampling, and standardized sample number.

FIG. 3.

Dendrogram derived from SmaI PFGE patterns of C. jejuni strains recovered from cattle feces samples and from the ceca of experimentally exposed broiler chickens.

FIG. 4.

Colonization of two independently housed groups of broiler chickens at 5 and 7 days following exposure to naturally occurring C. jejuni-contaminated calf feces samples at 16 days of age.