Abstract
BackgroundCampylobacter jejuni is a major zoonotic pathogen, causing gastroenteritis in humans. Invasion is an important pathogenesis trait by which C. jejuni causes disease. Here we report the genomic analysis of 134 strains to identify traits unique to hyperinvasive isolates.MethodsA total of 134 C. jejuni genomes were used to create a phylogenetic tree to position the hyperinvasive strains. Comparative genomics lead to the identification of mosaic capsule regions. A pan genome approach led to the discovery of unique loci, or loci with unique alleles, to the hyperinvasive strains.ResultsPhylogenetic analysis showed that the hyper-invasive phenotype is a generalist trait. Despite the fact that hyperinvasive strains are only distantly related based on the whole genome phylogeny, they all possess genes within the capsule region with high identity to capsule genes from C. jejuni subsp. doylei and C. lari. In addition there were genes unique to the hyper-invasive strains with identity to non-C. jejuni genes, as well as allelic variants of mainly pathogenesis related genes already known in the other C. jejuni. In particular, the sequence of flagella genes, flgD-E and flgL were highly conserved amongst the hyper-invasive strains and divergent from sequences in other C. jejuni. A novel cytolethal distending toxin (cdt) operon was also identified as present in all hyper-invasive strains in addition to the classic cdt operon present in other C. jejuni.ConclusionsOverall, the hyper-invasive phenotype is strongly linked to the presence of orthologous genes from other Campylobacter species in their genomes, notably within the capsule region, in addition to the observed association with unique allelic variants in flagellar genes and the secondary cdt operon which is unlikely under random sharing of accessory alleles in separate lineages.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2087-y) contains supplementary material, which is available to authorized users.
Highlights
Campylobacter jejuni is a major zoonotic pathogen, causing gastroenteritis in humans
We reveal mosaicism in the capsular polysaccharide (CPS) region and elsewhere in the genome with the apparent import of genes from C. jejuni subsp. doylei, C. lari and C. coli which may contribute to the hyper-invasive phenotype of these strains
The phylogenetic position of the six isolates was determined from a core genome alignment incorporating all available C. jejuni reference genomes as well as the 128 genomes previously sequenced by Sheppard et al [28]
Summary
Campylobacter jejuni is a major zoonotic pathogen, causing gastroenteritis in humans. Campylobacter jejuni is the major cause of gastroenteritis in humans worldwide. It is a self-limiting disease with the symptoms varying from watery diarrhoea with no inflammation to mucous containing bloody diarrhoea [1]. It is apparent that C. jejuni’s ability to adhere to and invade epithelial cells is influenced by the infection model or the type of intestinal cell line used [5,6,7]. It is strain dependent, often influenced by the severity of the clinical symptoms
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