Competing isogenic Campylobacter strains show variable population structures in vivo

University of Cambridge, Department of Veterinary Medicine; Institute for Animal Health, Compton; University of Cambridge, Department of Applied Mathematics and Theoretical Physics; University of Nottingham, School of Veterinary Medicine and Science

^* To whom correspondence should be addressed. Email: cc122{at}cam.ac.uk.

	Abstract

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 colonisation process at the molecular and population levels, both within and between hosts. Experiments employing competing strains of Campylobacter have been used to investigate colonisation. Implicit in these studies is the assumption that the behaviour 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), which have indistinguishable phenotypes in pure culture. Using mixtures of WITS it is possible to monitor the relative amounts of sub-populations of essentially wild-type bacteria. Using a two-week-old chicken model of colonisation 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 where birds inoculated with different WITS were co-housed. We present evidence for founder effects during initial colonisation with subsequent bird-to-bird transmission. We suggest that these and phenotypic variation contribute to the observed variability. These factors render simple models of colonisation which do not take them into account inappropriate for Campylobacter and impact the planning and interpretation of competition experiments using this organism.