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Applied and Environmental Microbiology, June 2008, p. 3857-3867, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02835-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Competing Isogenic Campylobacter Strains Exhibit Variable Population Structures In Vivo ^,

Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom,¹ Institute for Animal Health, Division of Microbiology, Compton Laboratory, Compton, Newbury, Berkshire, United Kingdom,² Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom,³ School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, Nottingham, United Kingdom⁴

Received 16 December 2007/ Accepted 11 April 2008

Consumption of poultry contaminated with Campylobacter jejuni is a risk factor for human gastrointestinal disease. The rational development of control strategies for Campylobacter within chickens requires an understanding of the colonization process at the molecular and population levels, both within and between hosts. Experiments employing competing strains of Campylobacter have been used to investigate colonization. Implicit in these studies is the assumption that the behavior of competing strains is reproducible between experiments. Variability in the recovery of mutants from the chicken gastrointestinal tract during signature-tagged mutagenesis studies demonstrated that this is not always the case. To further investigate this phenomenon in the absence of confounding factors due to phenotypic differences between mutants, we constructed individually identifiable wild-type isogenic tagged strains (WITS) that have indistinguishable phenotypes in pure culture. By using mixtures of WITS, it is possible to monitor the relative amounts of subpopulations of essentially wild-type bacteria. Using a 2-week-old chicken model of colonization, we observed unpredictable variations in population structure both within and between experiments, even in the simplest case of two competing strains. This variation occurred both when birds were simultaneously infected with two WITS and when birds inoculated with different WITS were cohoused. We present evidence for founder effects during initial colonization with subsequent bird-to-bird transmission. We suggest that these and phenotypic variation contribute to the observed variability. These factors render simple models of colonization which do not take them into account inappropriate for Campylobacter and impact the planning and interpretation of competition experiments using this organism.

Published ahead of print on 18 April 2008.

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