Submitted to: International Union of Microbiological Societies Proceedings/Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2004
Publication Date: 7/12/2005
Citation: Callicott, K., Hiett, K.L., Stern, N.J. 2005. Temporal population structure of campylobacter in broiler breeder chicken flocks in iceland [abstract]. International Union of Microbiological Society. p. 47-48. Interpretive Summary: The work presented discusses the dynamics of Campylobacter isolates within breeder flocks. In particular, it examines whether isolates collected from a particular flock at a particular time are less related to samples taken from the same flock at later points in time. In the absence of migration or strong selection, one expects the isolates from a flock to be closely related to other isolates from the same flock no matter when those other isolates were collected. There was an observed positive correlation between genetic distance between isolates and the length of time between when they were sampled, showing turnover in strains within flocks. This has implications for the control of Campylobacter in poultry production.
Technical Abstract: Campylobacter jejuni is a major cause of bacterial food-borne infection in the industrialized world, and the consumption of chicken is one of the most common sources of infection. Because it is a commensal of chickens, it might be thought that allele frequency would be relatively stable within a flock, but very little is known about allele dynamics within flocks. There are publications describing increasing genotypic diversity as broiler flocks mature, but how this process might play out over the much longer life of a breeder flock is unknown. High migration rates of Campylobacter between flocks or strong selection within flocks might cause a flock to be more closely related to its neighbors than to itself at an earlier or later point in time. Methods: The sequence of the flaA short variable region was determined for 289 Campylobacter isolated from 34 Icelandic breeder flocks at 18, 24, 40, and 60 weeks of age, although not all flocks have isolates at each time point. Genetic distance was calculated between population samples using pairwise FST values between sampling times within particular flocks and between sister flocks (arising from the same parent rearing flock) when these were sampled at the same point in time. A linear regression was performed between these FST values and the time between sample collection. Results: A significant positive regression was found between genetic distance and temporal distance (R2 = 0.0542, df=100, P < 0.05). Conclusions: Even though temporal distance explains only a small part of the variation in pairwise genetic distances, it indicates a significant turnover in alleles. Given the very large population size of Campylobacter within a breeder flock, one would expect limited genetic drift. This turnover in alleles may be the result of strong migration or of strong selection in the presence of high migration or mutation rates. Either cause--selection or migration--has ramifications for the control of Campylobacter in broiler production.