Multi-omics Approaches to Deciphering a Hypervirulent Strain of Campylobacter jejuni

Abstract

Campylobacter jejuni clone SA recently emerged as the predominant cause of sheep abortion in the United States and is also associated with foodborne gastroenteritis in humans. A distinct phenotype of this clone is its ability to induce bacteremia and abortion. To facilitate understanding the pathogenesis of this hypervirulent clone, we analyzed a clinical isolate (IA3902) of clone SA using multi-omics approaches. The genome of IA3902 contains a circular chromosome of 1,635,045 bp and a circular plasmid of 37,174 bp. Comparative genomic analysis revealed that IA3902 is most closely related to C. jejuni NCTC11168, which is a reference strain and was previously shown to be non-abortifacient in pregnant animals. Despite the high genomic synteny and sequence homology, there are 12 variable regions (VRs) and 8,696 single-nucleotide polymorphisms and indels between the two genomes. Notably, the variable genes in the capsular polysaccharides biosynthesis and O-linked glycosylation loci of IA3902 are highly homogenous to their counterparts in C. jejuni subsp. doylei and C. jejuni G1, which are known to be frequently associated with bacteremia. Transcriptomic and proteomic profiles were conducted to compare IA3902 with NCTC11168, which revealed that the pathways of energy generation, motility, and serine utilization were significantly up-regulated in IA3902, whereas the pathways of iron uptake and proline, glutamate, aspartate, and lactate utilization were significantly down-regulated. These results suggest that C. jejuni clone SA has evolved distinct genomic content and gene expression patterns that modulate surface polysacharide structures, motilitiy, and metabolic pathways. These changes may have contributed to its hyper-virulence in abortion induction.

Point mutations in the major outer membrane protein drive hypervirulence of a rapidly expanding clone of Campylobacter jejuni

“…Epidemiological analysis of historical clone SA isolates suggested that its emergence in the United States is likely to be a recent event (15), but the genetic basis for its emergence and enhanced virulence is unknown. To facilitate understanding the pathogenesis, we sequenced a representative clone SA isolate (IA3902), which revealed that the genome of IA3902 is highly syntenic to that of C. jejuni strain NCTC11168 (18). Importantly, C. jejuni NCTC11168 was shown to be nonabortifacient in pregnant animals (17), providing a closely related control strain for elucidating the hypervirulence of clone SA.…”

“…Comparative genomics revealed numerous genetic differences between the genomes of IA3902 and NCTC11168, including 57 unique genes and >8,000 SNPs as well as small (<10 bp) insertions and deletions (indels). Transcriptomic and proteomic analyses identified multiple differences in the expression of genes involved in several classical virulence-related pathways: iron acquisition, capsule biosynthesis, energy metabolism, and motility (18). However, the causative genetic changes driving clone SA's success in causing disease remained undetermined.…”

“…Purified genomic DNA of strain IA3902 was used as the donor DNA, whereas C. jejuni NCTC11168, which has a genome highly syntenic to that of IA3902 (18), was used as the recipient strain. Complete genome sequences are available for both strains, but 25 chromosomal genes and an extra plasmid are found to be specific for IA3902; in addition, 8,696 SNPs and indels were identified between these two strains (18,19). Thus, individual analyses of the contribution of these differences to virulence would be time and cost prohibitive, which demanded for an effective and high throughput strategy for screening the candidate loci.…”

“…Transformation efficiency was monitored by measuring the frequency of tetracycline-resistant colonies. The recipient NCTC11168 is tetracycline susceptible, whereas IA3902 is resistant due to the possession of a chromosomal tet(O) gene (18). The frequency of tetracycline-resistant transformants plateaued after four passages (SI Appendix, Fig.…”

Genetic Diversity and Antimicrobial Susceptibility of Campylobacter jejuni Isolates Associated with Sheep Abortion in the United States and Great Britain

“…Recently, we reported that clone SA has emerged as a zoonotic pathogen, causing human gastroenteritis linked mainly to the consumption of raw milk (13). The genome of a representative of this clone, C. jejuni IA3902, has now been sequenced (15).…”