Studies were performed on a cytotoxin (CT) from human strains of Campylobacter jejuni isolated in Malaysia. CT was detected by cytopathic effect (CPE) on HeLa cells at titres from 8 to 32, in culture filtrates from 14 (48%) of 29 human isolates. The CPE correlated well with a quantitative 51Cr-release assay where a specific release of 54-68% was noted. CT production was lost after 5-7 subcultures. CT activity was also detected in 5 (26%) of 19 faecal filtrates from which CT-producing isolates were subsequently obtained. The mol. wt of CT was estimated by Sephadex G-50 chromatography to be greater than 30,000. In a suckling-mouse assay, CT consistently failed to demonstrate fluid accumulation after intragastric inoculation of culture filtrate. The Removable Intestinal Tie Adult Rabbit Diarrhoea (RITARD) assay was also used. Rabbits given CT-producing strains of C. jejuni developed bacteraemia and severe watery mucus-containing diarrhoea for the duration of the experiment with death of some animals. Rabbits given CT non-producing strains had less severe disease and none died. Rabbits given partially-purified CT had diarrhoea for 3 days but none died.
Approximately 57% of clinical and 33% of poultry isolates examined produced a cytotoxin. Cytotoxic activity was detected in 25 (50%) isolates of Campylobacter of which 12 were isolated from bloody diarrhea and 9 from watery stools. The cytotoxin titers were low, ranging from 2 to 16. The crude filtrates from 50 Campylobacter isolates showed no cytotoxic effect in Vero cells, no fluid accumulation in suckling mice and no hemolytic activity.
Eighty-six clinical isolates of Aeromonas hydrophila were studied for their ability to produce four exotoxins: a haemolysin active against rabbit erythrocytes, cytotoxin and enterotoxin detectable with Vero cell cultures, and the cholera toxin-like factor detected by an enzyme-linked immunosorbent assay. At least one exotoxin was produced by 80% of enteric and 96% of non-enteric isolates. The exotoxin profiles of non-enteric isolates were more restricted than those of enteric isolates, with haemolysin and cytotoxin producers preponderant. Although haemolysin and cytotoxin were produced by isolates from all sources, the enterotoxin and cholera toxin-like factor were more common amongst enteric isolates. The production of haemolysin and cytotoxin were closely related but the association between the enterotoxin and the cholera toxin-like factor was not significant.
Eighteen strains of Aeromonas hydrophila from patients with bacteraemia were investigated for possible virulence factors. Cytotoxin and haemolysin were produced by all strains, whereas cholera toxin-like factor was produced by 33% of strains only. Enterotoxin production was not detected. Haemagglutination of guinea-pig, fowl and rabbit erythrocytes was demonstrated by 83%, 67% and 61% of strains, respectively. Fucose- and mannose-sensitive haemagglutinins were predominant. None of the strains agglutinated sheep erythrocytes. Extrachromosomal DNA was detected in 17 strains, 16 of which had a plasmid (3.6-5.1 MDa), the majority being between 4.6 and 5.1 MDa.