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