The primary aim of this study was to investigate whether the Campylobacter jejuni strains causing two clinically distinct form of diarrhoea i.e. cholera-like watery diarrhoea (Group C strains) and dysentery-like mucoid diarrhoea (Group D strains) possess unique sets of virulence characteristics. For this purpose C. jejuni strains were assayed for a number of putative virulence factors and the results of the Group C strains were compared with those of Group D strains to assess whether these candidate virulence markers show any significant association with any particular group of strains. Initially, a comperative study of the enterotoxigenicity of Group C and D of strains was conducted The infant chicken model of Sanyal et al (1984a) proved unsatisfactory as convincing evidence of diarrhoea was not obtained. Subsequently, the new-borne chick diarrhoea model of Welkos (1984) was adopted which proved useful for this purpose. Attention was then turned to determine whether plasmids were involved in the enterotoxin production by C. jejuni strains. This aspect of study stemed from the preliminary report by Lee et al (1985) that the production of enterotoxin detectable by Chinese hamster ovary (CHO) cell assay was mediated by a 46.5 Kilo-base transmissible plasmid. No correlation between plasmid profile and enterotoxigenicity was noted in this study. The in vitro assays, GM1 ganglioside ELISA and CHO cell assay were found to suitable for quantitation of enterotoxin produced by the C. jejuni strains and the assays correlated well with each other. Enterotoxigenicity was predominantly associated with the Group C strains. Lines of partial identity were obtained between cholera toxin and C. jejuni enterotoxin in immunodiffusion experiments. No hybridization was however noted between Hind III digested chromosomal DNA of 4 enterotoxigenic C.jejuni strains and the E. coli LT B subunit gene probe. After successfully demonstrating the enterotoxigenic nature of C. Jejuni strains in the new-born chick model and in vitro assays (GM1 ganglioside ELISA and CHO cell assay), it was decided to explore whether the ligated ileal loop for fluid accumulation could be performed in infant chicks. Reproducible positive results were obtained in 5-day-old chicks, both with whole cells and cell- free culture supernates. This is the first report of accumulation of fluid in the ligated ileal loop of chickens by C. jejuni. C. jejuni strains produced an extracellular haemolysin active against a range of erythrocytes but not against chicken erythrocytes. The haemolytic factor lost its activity partially upon heat-treatment and was trypsin sensitive. The haemolysin which was also cytotoxic towards HeLa cells was predominantly produced by Group D strains. Adherence and invasion potentials of the C. jejuni strains were evaluated in the HeLa cell model by quantitative bacterial counts. The C. jejuni strains differentially adhered to and invaded HeLa cells. The Group D strains were significantly more invasive than the Group D strains, but the adherence of the strains belonging to the two groups did not differ significantly. However, the individual strains belonging to the two groups exhibited widely overlapping adherence and invasion potentials. Adherence and invasion of representative strains from both groups were significantly inhibited by L-fucose, cytochalasin B, chicken intestinal mucus and antiserum raised against formalinized bacterial cells. The results of this study have established the importance of working with a range of clinical isolates because they revel a spectrum of virulence. It seems probable that the degree of virulence of a particular strain is influenced by the expression of a number of virulence factors.
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