Identification and characterization of virulence associated factors of C. jejuni
Campylobacter jejuni, an important food-borne human bacterial pathogen in industrialized countries and in the developing world, the leading cause of bacterial diarrhoea. The infection may be accompanied by fever and abdominal cramps and, as a post-infection complication, in rare cases Guillain-Barré syndrome might emerge. In contrast, C. jejuni is only a commensal in poultry, where the pathogen predominantly resides in the cecum which contains many anaerobic fermentative bacteria. Within these natural habitats, C. jejuni is able to metabolize products like free amino and keto acids that have been generated by these bacterial species or from the host himself.In order to identify genes which are related to the invasion of host cells by the pathogen, 660 clones of a transposon mutant library generated in the clinical C. jejuni isolate B2 were screened. Thereby, a clone with a transposon insertion in gene cj0952c was identified. As in the sequenced C. jejuni strain NCTC 11168, the respective protein together with the gene product of adjacent gene cj0951c consists of two transmembrane domains, a HAMP domain followed by C-terminal putative MCP domain together believed to act as a chemoreceptor, designated as Tlp7. This thesis describes that genes cj0952c and cj0951c are important for the invasion of host cells by the pathogen. In addition, it is clearly shown that both genes are not translated as one protein in C. jejuni isolate B2 contradicting the idea of a postulated read-through mechanism. Moreover, these genes are responsible for reduced motility of C. jejuni and alter the chemotactical behavior of the pathogen towards formic acid. Finally, growth curve analysis indicates that these genes are not related to the utilization of formic acid by formate dehydrogenase.A second gene investigated in this thesis with regard to reduced infectivity of C. jejuni isolate B2 is cj0005c, which encodes a molybdopterin oxidoreductase. Together with the monohaem cytochrome c oxidoreductase subunit encoded by cj0004c, both subunits constitute a sulphite: cytochrome c oxidoreductase (SOR). Since C. jejuni lacks the glycolytic enzyme phosphofructokinase, glucose cannot be catabolized and other products serve as electron donors, e.g. succinate, malate, formate, D-lactate, hydrogen and NAD(P)H. The possession of a sulphite oxidation system is believed to be important for C. jejuni to survive in food which has been treated with sulphite for preservative reasons, as well as in humans since it has been shown that sulphite is also released by neutrophils as part of the host defense. In this thesis SOR is docummented to be an important virulence factor of C. jejuni by reducing the motility of the pathogen and by the downregulation of C. jejuni genes known to belong to the virulence repertoire of the pathogen.
570 Biowissenschaften, Biologie, Biologie, Campylobacter jejuni;invasion, formic acid;Motility, 42, WF 200: Molekularbiologie
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