Strain-Specific Insights Into the Different Diarrheal Manifestations of Campylobacter jejuni and the Role of Racrs in Pathogenesis

Abstract

Campylobacter jejuni is an undervalued globally important foodborne pathogen that remains severely understudied. It is considered to be the most common cause of bacterial gastroenteritis worldwide, with acute infections leading to several post infectious ailments, along with long term effects on childhood development. The increasing prevalence worldwide and rise in antibiotic resistance, highlights the importance in understanding how this pathogen causes disease and how it can be prevented. In humans, C. jejuni infections lead to two different diarrheal presentations, a watery diarrhea or a bloody/inflammatory diarrhea. Yet in the past 40 years, there has been little to no research aimed at understanding these diarrheal manifestations and the underlying mechanisms behind what drives them. The production of disease is multifactorial and involves both host and bacterial factors that influence the patient outcome. C. jejuni pathogenicity and virulence factors such as invasiveness and toxin production are suggested to contribute to the production of disease in humans. Furthermore, bacterial regulatory systems allow bacteria to adapt to changing environmental conditions, by altering gene expression. This dissertation will address how bacterial pathogenicity, virulence and growth factors as well as the regulatory system RacRS all influence strains of C. jejuni associated with two different diarrheal manifestations in the neonatal piglet model. While the neonatal piglet model is not a direct reflection of disease presentation in humans, it is the only animal model that distinguishes between diarrhea manifestations caused by C. jejuni and has prominent similarities to humans both physiologically and anatomically. Chapter 1 highlights the global epidemiology of C. jejuni, detailing its prevalence across different geographical regions, transmission routes and the various environmental and host factors influencing infection rates. This chapter also provides an in-depth review of the pathogenesis of C. jejuni infections, from ingestion to its interactions with the host immune response and associated post infectious sequalae. Certain aspects of C. jejuni pathogenesis such as adhesion and the use of the flagellar secretion system have been extensively studied, but significant gaps remain in the understanding of how this pathogen coordinates disease progression in humans. Furthermore, this chapter reviews C. jejuni two component regulatory systems with specific emphasis on the RacRS system and its role in disease production in C. jejuni. Chapter 2 establishes the variations in pathogenicity and virulence factors among C. jejuni strains associated with watery and bloody/inflammatory diarrhea in the neonatal piglet model. By comparing the phenotypes of C. jejuni strains with known diarrheal manifestations, this chapter explores how toxin production, invasion, attachment, macrophage survivability, immune response and epithelial integrity all contribute to these distinct outcomes. These findings provide a clearer picture of strain-specific virulence and pathogenicity factors and how they play into disease production. Chapter 3 expands upon the observed pathogenicity and virulence differences between C. jejuni strains associated with watery and bloody/inflammatory diarrhea in the neonatal piglet model that mimics key aspects of human gastrointestinal infection. It explores how these strains respond at the body temperature of humans as well as the body temperature of poultry, the natural reservoir of C. jejuni, by examining their metabolic adaptations across both hosts. By investigating growth and carbon utilization patterns between these two groups of C. jejuni, potential bacterial lifestyle preferences are observed. The role of growth patterns and nutrient availability provides a more complete understanding of how C. jejuni may survive and adapt to the human gut. Chapter 4 integrates the findings in the previous chapters to establish a link between the RacRS regulatory system and the established diarrheal manifestations of C. jejuni strains in the neonatal piglet model. This chapter builds on the limited prior research on RacRS by examining how RacRS influences pathogenicity and virulence factors such as motility, attachment, invasion, toxin production, biofilm production and macrophage survivability. These findings suggest a distinct role for RacRS in the factors that help to establish early colonization and infection within human hosts.