Campylobacter jejuni - The Search for virulence-associated factors

In recent years Campylobacter jejuni replaced Salmonella spp. as the most common bacterial cause of food-borne gastroenteritis worldwide. Noticeable is the fact that no classical enterotoxins are known for C. jejuni. The sequencing of the complete genome revealed that C. jejuni possesses one single trimeric cytotoxin, called cytolethal distending toxin (CdtABC). Other previously suspected toxins could not be confirmed by sequence analysis. However, a number of alternative virulence-associated factors have been identified so far. The multidrug efflux pump CmeABC faciliates, by "neutralization" of bile salts, the survival of C. jejuni in the avian as well as in the human intestine. Furthermore it is responsible for resistance to heavy metal ions and to certain antibiotics. The flagellum of C. jejuni mediates not only the targeted motility directed by three families of chemo- and aerotaxis receptors. A homologue of a type-III-secretion-system integrated in the flagellar apparatus is functionally involved in the cell-invasion process. Thus, a whole group of proteins termed Campylobacter invasion antigens (Cia) is injected into the host cell via the flagellar transport mechanism during the process of host cell invasion. Further pathogenicity-associated determinants are the polysaccharide capsule and specific glycosylation of the lipooligosaccharide (LOS). It has been shown that C. jejuni strains with sialylation of the lipooligosaccharide display increased invasiveness. These strains are also responsible for the development of the Guillain-Barre-syndrome, through molecular mimicry with gangliosides of the central nervous system. In the past, many colonization-related factors have been identified with the help of transposon-induced mutagenesis and chicken colonization models. Using this and other modern molecular biology methods, combined with appropriate animal models such as gnotobiotic mice in which symptomatic campylobacteriosis can be established, it is hoped to identify additional virulence-associated factors.