Investigation of the contributions of phase variation to colonisation, gastrointestinal spread and liver invasion in chickens by Campylobacter jejuni

Abstract P6

Presenter: Caroline Cayrou (University of Leicester)

The foodborne pathogen, Campylobacter jejuni, is usually found in the gastro intestinal tract (GI) of the chickens but can cross the GI epithelial barrier and invade internal tissues. One important mechanism used by C. jejuni to survive changing environments, including phage infection and immune responses, is phase variation (PV) due to mutations in mononucleotide repeat tracts. Our aim is to assess the contributions of PV to invasion of chicken tissues by assessing the invasiveness of different C. jejuni isolates and whether the phase variation status differs between infection sites. The genomes of 39 C. jejuni isolates were sequenced and analysed. These C. jejuni isolates were obtained from the caeca, ileum or liver of 25 chickens of one flock. Those isolates belonged mainly to two different clonal complexes (CCs) cc353 and cc464. We observed that cc353 isolates tend to colonise preferentially the GI of the chickens (80.9% GI isolates) whereas cc464 isolates tend to invade the liver (91.6% liver isolates). Using PhasomeIT analysis, we identified 33 and 32 potential phase variable genes in the cc353 and cc464 sequences, respectively and developed strain-specific PV assays combining multiplex PCR with fragment length analysis. These PV assays allow for exploration of PV status during exposure of the cc353 and cc464 isolates to selective conditions. In order to explore the role of PV during chicken colonisation and spread to host tissues, we performed an in-vivo infection of broiler chickens. Sets of birds were gavaged with either the cc353 and cc464 chicken isolates or two laboratory isolates, M1 and NCTC11168. Bacterial colonies were obtained from the inoculum and homogenates of caeca, ileum, spleen and liver of infected birds after 14 days of infection. Twenty colonies from the inoculum and each tissue were analysed for PV status. Comparisons between PV status of the bacterial populations from the inoculum and infected tissues will allow us to determine if PV of specific genes is involved in chicken colonisation. These studies will improve our understanding of mechanisms that facilitate spread of C. jejuni within chicken tissues and through the foodchain. This study is part of the CampAttack project funded by the BBSRC.

Presenting in Speaking session 2 - Pathogenesis