Survival Mechanisms of Campylobacter hepaticus Identified by Genomic Analysis and Comparative Transcriptomic Analysis of in vivo and in vitro Derived Bacteria

Abstract

Chickens infected with Campylobacter jejuni or Campylobacter coli are largely asymptomatic, however, infection with the closely related species, Campylobacter hepaticus, can result in Spotty Liver Disease (SLD). C. hepaticus has been detected in the liver, bile, small intestine and caecum of SLD affected chickens. The survival and colonization mechanisms that C. hepaticus uses to colonize chickens remain unknown. In this study, we compared the genome sequences of 14 newly sequenced Australian isolates of C. hepaticus, isolates from outbreaks in the United Kingdom, and reference strains of C. jejuni and C. coli, with the aim of identifying virulence genes associated with SLD. We also carried out global comparative transcriptomic analysis between C. hepaticus recovered from the bile of SLD infected chickens and C. hepaticus grown in vitro. This revealed how the bacteria adapt to proliferate in the challenging host environment in which they are found. Additionally, biochemical experiments confirmed some in silico metabolic predictions. We found that, unlike other Campylobacter sp., C. hepaticus encodes glucose and polyhydroxybutyrate metabolism pathways. This study demonstrated the metabolic plasticity of C. hepaticus, which may contribute to survival in the competitive, nutrient and energy-limited environment of the chicken. Transcriptomic analysis indicated that gene clusters associated with glucose utilization, stress response, hydrogen metabolism, and sialic acid modification may play an important role in the pathogenicity of C. hepaticus. An understanding of the survival and virulence mechanisms that C. hepaticus uses will help to direct the development of effective intervention methods to protect birds from the debilitating effects of SLD.

Campylobacter hepaticus, the Cause of Spotty Liver Disease in Chickens: Transmission and Routes of Infection

“…Two isolates contained plasmids with very high sequence similarity to C. jejuni pTet-like plasmids. C. hepaticus isolates from Australia and UK have previously been reported to contain tetracycline-resistant plasmids, but they contained different C. jejuni and C. coli plasmids (11,12). Currently, chlortetracycline is the main treatment option available for the control of SLD in Australia.…”

“…Campylobacter hepaticus ranges in size from 0.3 to 0.4 µm wide and 1.0-1.2 µm long (3,8,9). Campylobacter hepaticus has a reduced genome size (1.48-1.51 Mb) and a lower G+C content (27.9-28.5%) than most Campylobacter species (11,12). Campylobacter hepaticus grows slowly in vitro; requiring at least 3 days for visible colonies to form on blood agar (3,8).…”

A review of the novel thermophilicCampylobacter,Campylobacter hepaticus,a pathogen of poultry

“…In a detailed analysis of the genome of Australian and UK isolates of C. hepaticus , Van et al () showed that clonal populations of C. hepaticus were geographically confined. They also demonstrated that there was divergence from the other Campylobacter infecting poultry ( C. jejuni and C. coli ) indicating that there were barriers to gene transfer between these species.…”

Development of an enzyme-linked immunosorbent assay for detecting Campylobacter hepaticus specific antibodies in chicken sera – a key tool in Spotty Liver Disease screening and vaccine development

“…In another challenge, the C. hepaticus 44L strain was used and the assay successfully detected antibodies induced by this strain (data not shown). It has been reported that the genomes of C. hepaticus strains are highly similar (Van et al 2019), therefore the expectation is that the immunoassay could reliably test antibody responses produced by other C. hepaticus strains.…”

“…The cross reactivity of C. hepaticus antigens with antibodies to other common campylobacters was anticipated to be one of the major challenges in developing a species-specific assay. Nearly 70% of the genes in C. hepaticus are conserved in C. jejuni and C. coli strains (Van et al, 2019). It is not uncommon to find C. jejuni and C. coli in flocks since most chickens get exposed to them early in their life and a majority harbour them as commensal bacteria in the intestine and caecum (Lindblom et al, 1986;Van et al, 2018).…”