Abstract Infection by Campylobacter is recognised as the most common cause of foodborne bacterial illness worldwide. Faecal contamination of meat, especially chicken, during processing represents a key route of transmission to humans. There is currently no licenced vaccine and no Campylobacter -resistant chickens. In addition, preventative measures aimed at reducing environmental contamination and exposure of chickens to Campylobacter jejuni (biosecurity) have been ineffective. There is much interest in the factors/mechanisms that drive C. jejuni colonisation and infection of animals, and survival in the environment. It is anticipated that understanding these mechanisms will guide the development of effective intervention strategies to reduce the burden of C. jejuni infection. Here we present a comprehensive analysis of C. jejuni fitness during growth and survival within and outside hosts. A comparative analysis of transposon (Tn) gene inactivation libraries in three C. jejuni strains by Tn-seq demonstrated that a large proportion, 331 genes, of the C. jejuni genome is dedicated to ( in vitro ) growth. An extensive Tn library in C. jejuni M1cam (~10,000 mutants) was screened for the colonisation of commercial broiler chickens, survival in houseflies and under nutrient-rich and–poor conditions at low temperature, and infection of human gut epithelial cells. We report C. jejuni factors essential throughout its life cycle and we have identified genes that fulfil important roles across multiple conditions, including maf3, fliW, fliD, pflB and capM , as well as novel genes uniquely implicated in survival outside hosts. Taking a comprehensive screening approach has confirmed previous studies, that the flagella are central to the ability of C. jejuni to interact with its hosts. Future efforts should focus on how to exploit this knowledge to effectively control infections caused by C. jejuni . Author Summary Campylobacter jejuni is the leading bacterial cause of human diarrhoeal disease. C. jejuni encounters and has to overcome a wide range of “stress” conditions whilst passing through the gastrointestinal tract of humans and other animals, during processing of food products, on/in food and in the environment. We have taken a comprehensive approach to understand the basis of C. jejuni growth and within/outside host survival, with the aim to inform future development of intervention strategies. Using a genome-wide transposon gene inactivation approach we identified genes core to the growth of C. jejuni . We also determined genes that were required during the colonisation of chickens, survival in the housefly and under nutrient-rich and –poor conditions at low temperature, and during interaction with human gut epithelial tissue culture cells. This study provides a comprehensive dataset linking C. jejuni genes to growth and survival in models relevant to its life cycle. Genes important across multiple models were identified as well as genes only required under specific conditions. We identified that a large proportion of the C. jejuni genome is dedicated to growth and that the flagella fulfil a prominent role in the interaction with hosts. Our data will aid development of effective control strategies.

Genome-Wide Fitness Analyses of the Foodborne PathogenCampylobacter jejuniinIn VitroandIn VivoModels