Short-term evolution in Campylobacter jejuni is concentrated in genes associated with movement

Campylobacter cause acute gastroenteritis in humans with the infection frequently beingtransmitted by poultry meat. Although many studies have examined the epidemiologyof this bacterium, and others have studied long-term evolution, few have considered theshort-term evolutionary dynamics following inoculation with fully characterised strains.The present study involved a randomised trial of the effect of an in-feed additive onCampylobacter colonisation of chickens. In total 176 chickens were challenged with twoC. jejuni genotypes and the evolution of the Campylobacter population over 43 dayswas explored using multilocus sequence typing and full genome sequencing. The birdswere inoculated with an equal mixture of an isolate from each of two sequence types,ST-474 and ST-45. One hundred and sixty-eight isolates collected at the different killdays were multilocus sequence typed, but only isolates with the sequence type ST-474were recovered.Twenty-seven of the 168 isolates cultured from the caeca of 12 birds plus the twoinoculum strains were whole genome sequenced and analysed. No evidence ofrecombination between the ST-45 and ST-474 strains was detected. We observed 15core single nucleotide polymorphisms (SNPs) and three non-core SNPs across theST-474 isolates (compared to the inoculum ST-474 isolate). Fourteen of the core SNPswere non-synonymous point mutations confined to only nine genes which were allassociated with cell shape, chemotaxis or motility of the bacteria. We identified sixindependent SNPs in a single gene, mreB, a homologue of actin, two of which have alsobeen identified in isolates from Oxford, UK, suggesting parallel evolution. We identifiedalterations in the motility of the bacteria which could be associated with the detectedSNPs.