Virulome analysis of extra-intestinal Campylobacter jejuni and Campylobacter coli from commercial chickens

Abstract P2

Presenter: Alessandra Piccirillo (University of Padua)

Campylobacter jejuni and C. coli are one of the most common cause of acute gastroenteritis in humans. In domestic animals, including poultry, these two campylobacters are considered mainly as harmless inhabitants of the intestinal tract, usually without causing any signs of disease. In the last years, however, some studies have shown that these campylobacters may invade the chicken intestinal wall and reach other organs, such as the liver. A comparative whole genome analysis was performed with the aim to identify virulence factors that could be associated with the extra-intestinal spread of C. jejuni and C. coli. Nine C. jejuni and five C. coli were isolated from the liver or the spleen of broilers (n = 5), laying hens (n = 8) and capons (n = 1). At necropsy, dead birds showed hepatic focal necrosis, i.e. foci of 1-2 mm diameter, disseminated, coalescent and greyish-white in colour. C. jejuni and C. coli isolates were confirmed by using MALDI-TOF MS and end-point PCRs. The genomes of the 14 isolates were fully sequenced with the Illumina Technology on the NextSeq 500 platform. After de-novo assembling of the raw sequences, multilocus sequence types (STs), whole genome-based phylogeny, and virulome characterization were performed by using PubMLST database, CLC Genomics Workbench 12, and Whole Genome Sequence Typing Database (BacWGSTdb) and Virulence Factor Database (VFDB), respectively. Whole genome analysis showed a wide genetic diversity among the 14 isolates since MLST analysis revealed 7 different STs for C. jejuni (STs 354, 400, 880, 2116, 2274, 2314 and 2863) and 5 for C. coli (STs 855, 892, 1585 and 4743 and the novel ST 10568), while 10 different phylogenetic clusters (5 clusters per species) were identified. Among 133 virulence-associated genes, motility (e.g., flaA and flaB), adherence (e.g., cadF), invasion (e.g., flhA and flhB) and toxin (e.g., wlaN) determinants were recognized. Furthermore, the isolates harboured a higher number of virulence-associated genes compared to reference genomes (mean gene no. 108, 44 C. jejuni isolates vs. 70 C. jejuni reference genomes; mean gene no. 74,4 C. coli isolates vs. 57,8 C. coli reference genomes). This comparative study showed that C. jejuni and C. coli associated with hepatic lesions in commercial chickens were highly diverse and hosted a high number of virulence-associated genes. These findings suggest that such genetic features might be related to the pathological lesions, caused by campylobacters extra-intestinal spread and colonization of parenchymatous tissues.

Presenting in Speaking session 2 - Pathogenesis