Virulence traits of Aeromonas strains in relation to species and source of isolation

The virulence traits of 39 well-defined clinical (29 strains) and environmental (10 strains) isolates of Aeromonas (16 A. hydrophila, 12 A. sobria and 11 A. caviae) were examined by a variety of assays to delineate differences, if any, in the enteropathogenic potential in relation to species and the source of isolation. The distribution of enterotoxin (ent), cytotoxin (cyt) and haemolysin (hae) producing strains of Aeromonas did not correlate to species and source of isolation. The extracellular virulence phenotype Ent+ Cyt+ Hae+ was the most common one among all the three species although unique phenotypes associated prominently with either A. hydrophila or A. sobria were also discernible. None of the cytotoxin or haemolysin producing strains hybridized with the vt1/vt2 or the tdh/trh gene probes, respectively, indicating that these two factors of Aeromonas were distinct. Haemagglutination of human O group erythrocytes was not related to the source of isolation or production of enterotoxin, cytotoxin or haemolysin but appeared to be related to species. The strains which did not exhibit cell-associated haemagglutination belonged to either A. hydrophila or A. caviae. Haemagglutination unaffected by fucose, mannose and galactose was the dominant inhibition pattern exhibited mainly by the clinical haemagglutinating strains of the three species. Only one clinical strain of A. caviae showed a diffuse pattern of adherence to HeLa cells. Expression of the 5 bacterial enzymes by strains of Aeromonas did not fall into a readily discernible pattern in relation to species or source of isolation. From this study, it is clear that the mechanism of the pathogenesis of Aeromonas is a multifactorial one.

Purification of enterotoxins from Vibrio mimicus that appear to be identical to cholera toxin

Cholera toxin-like (CT-like) enterotoxins produced by two strains of Vibrio mimicus, 61892 and 63616, isolated from diarrhea patients in Bangladesh, were purified, and their physicochemical, biological, and immunological properties were compared with those of CT produced by classical Vibrio cholerae 569B. The CT-like toxins were produced by lincomycin-resistant mutants grown in the presence of lincomycin at 200 micrograms/ml for strain 63616 and 250 micrograms/ml for strain 61892 and were purified by coprecipitation with hexametaphosphate followed by chromatography on phosphocellulose. The pure CT-like toxins were indistinguishable from 569B CT in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, rabbit intestinal loop and Y-1 adrenal cell assays, antiserum neutralization and binding inhibition assays, and Ouchterlony immunodiffusion, except that the CT-like toxins appeared to consist almost entirely of A subunit which was proteolytically unnicked. Trypsin nicking, however, resulted in fragments that appeared to be identical to those of 569B CT. These results indicate that at least one species of Vibrio other than V. cholerae can produce enterotoxins which are virtually identical to CT.

Evidence that a non-O1 Vibrio cholerae produces enterotoxin that is similar but not identical to cholera enterotoxin

Cholera-like enterotoxin produced by a non-O1 strain of Vibrio cholerae, S7 (S7 enterotoxin), isolated from human diarrheal stool, was purified, and its physicochemical, biological, and immunological properties were compared with those of cholera enterotoxin from V. cholerae O1 569B (CT) and an enterotoxin produced by another non-O1 V. cholerae (E8498 enterotoxin) reported previously (Yamamoto et al., Infect. Immun. 39:1128-1135, 1983). The purified S7 enterotoxin had physicochemical properties different from those of CT and E8498 enterotoxin. S7 enterotoxin had greater relative mobility in conventional polyacrylamide gel disc electrophoresis and a lower isoelectric point, and its B subunit was smaller than those of CT and E8498 enterotoxin. The results of sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis suggested that the size of the aggregate of the B subunits of S7 enterotoxin is larger than that of CT and E8498 enterotoxin. The biological and immunological properties of S7 enterotoxin were indistinguishable from those of CT and E8498 enterotoxin. These results indicate that non-O1 vibrios may produce more than one kind of cholera-like enterotoxin: one which is identical to CT (E8498 enterotoxin type) and another which is not identical to CT (S7 enterotoxin type).

Enterotoxin production by Vibrio cholerae and Vibrio mimicus grown in continuous culture with microbial cell recycle

We have examined the effect of complete cell recycle on the production of cholera toxin (CT) by Vibrio cholerae and CT-like toxin by Vibrio mimicus in continuous culture fermentations. Complete cell recycle was obtained by filtering culture fluids through Amicon hollow fibers with an exclusion limit of 100,000 daltons (H1P100-20) and returning the concentrated cell slurry to the fermentor. A single 1-liter laboratory fermentor system modified with this recycle loop was capable of producing over 20 liters of cell-free culture filtrate per day. Toxin production in this system was compared with yields obtained in traditional continuous cultures and in shake flask cultures. Yields of CT from V. cholerae 569B in the recycle fermentor were highest at the highest dilution rate employed (1.0 vol/vol per h). The use of complete cell recycle dramatically increased yields over those obtained in continuous culture and equaled those obtained in shake flasks. The concentration of CT in the filtrate was slightly less than half of that measured in culture fluids sampled at the same time. Similarly, V. mimicus 61892 grown in the presence of 50 micrograms of lincomycin per ml produced 280 ng of CT per ml in the recycle fermentor, compared with 210 ng/ml in shake flasks under optimal conditions. The sterile filtrate from this fermentation contained 110 ng/ml.

Purification and some properties of a non-o1 Vibrio cholerae enterotoxin that is identical to cholera enterotoxin

Cholera-like enterotoxin was isolated and purified from the culture supernatant of a non-O1 strain of Vibrio cholerae, E8498, isolated from the environment. Enterotoxin was purified by aluminum hydroxide absorption and elution and successive gel filtrations on Sephadex G-100, Bio-Gel A-5m, and Sephadex G-75. Purified enterotoxin gave a single stained band on polyacrylamide gel disc electrophoresis, and the mobility was the same as that of cholera enterotoxin. The specific biological activity of the purified enterotoxin was almost the same as that of cholera enterotoxin in the Chinese hamster ovary cell assay, fluid accumulation in mouse ligated intestine, increase in vascular permeability in rabbit skin, and passive immune hemolysis. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis showed that the purified enterotoxin consisted of subunits A and B, identical to those of cholera enterotoxin, and Ouchterlony double gel diffusion tests indicated that the two toxins were immunologically identical. Enterotoxins prepared from several non-O1 strains isolated from human patients were also immunologically identical to cholera enterotoxin.