Molecular characterization and differentiation of Campylobacter fetus subspecies

The bacterium Campylobacter fetus (C. fetus) can cause disease in humans and animals. In humans, C. fetus can cause septicemia and intestinal illness. Contaminated food, like unpasteurized milk, is possibly a source of human C. fetus infections. This thesis focuses on the mammal-associated C. fetus subsp. fetus (Cff) and C. fetus subsp. venerealis (Cfv). Cfv is described as the causative agent of Bovine Genital Campylobacteriosis (BGC), a syndrome characterized by infertility and abortion in cattle. Cff and Cfv can be differentiated with two biochemical tests. Nowadays, the BGC control programs focus only on Cfv and not Cff, while it is described that Cff can also cause abortions in cattle. The aim of this thesis was to study the molecular characteristics of the C. fetus strains. Furthermore, we studied if we could associate the molecular characteristics with the virulence of the strains. It is known that the biochemical tests used to differentiate Cfv and Cfv are not always reliable. In this study, we tested all available molecular methods and showed that none of these methods could reliable differentiate the C. fetus strains. To improve current diagnostics, we developed a novel PCR assay, which was able to differentiate Cff from Cfv strains reliable. During the study, C. fetus strains were sequenced and we determined the molecular characteristics. The classification of the strains based on the molecular characteristics was not consistent with the classification based on the biochemical tests. The BGC control programs use the biochemical tests to differentiate between Cff and Cfv, while this differentiation cannot be associated with the virulence of the strains. It is more important for the BGC control programs to differentiate between virulent and non-virulent C. fetus strains. Therefore, we studied the presence of type IV secretions systems (T4SSs), a potential virulence factor, in the strains and revealed that C. fetus strains can contain multiple T4SSs, which were not Cfv-specific, but also found in Cff strains. The results of this thesis showed that the classification of C. fetus strains based on their molecular characteristics was not consistent with the biochemical characteristics of the strains. Furthermore, it was revealed in this study that Cfv has recently diversified from a Cff ancestor, indicating that Cfv is most likely not a different subspecies, but more likely a Cff clone restricted to the genital tract of cattle. In the C. fetus strains, several potential virulence factors were identified, including T4SSs, but we could not associate these factors with the clinical characteristics of strains. Further research is necessary to unravel the role of the potential virulence factors in C. fetus pathogenesis