Heat-Stable Enterotoxin Produced by Yersinia enterocolitica Isolated from Patients

Twenty-three strains of Yersinia enterocolitica were isolated from children with gastrointestinal illness and examined for the production of enterotoxins by using both suckling mouse and Chinese hamster ovary (CHO) cell assay systems. Six strains were found to be enterotoxigenic in the suckling mouse assay, but all strains were negative in the CHO cell assay. Enterotoxin was detected in the culture supernatant when organisms were grown at 25 C but not at 37 C. Enterotoxin in a 15-fold concentrated culture supernatant was precipitated by adding absolute ethanol to a concentration of 90%. However, after being dialyzed against distilled water in Spectra/por 6 membrane tubing, it was soluble in 80% acetone. One unit dose of partially purified enterotoxin was 5.0 µg of protein/mouse in the suckling mouse assay. The molecular weight of enterotoxin was between 10,000 and 50,000 daltons as determined by ultrafiltration. It was stable to heat (121 C × 20 min or 100 C × 60 min). These observations indicate that Y. enterocolitica isolated in Japan also produce an enterotoxin similar to the heat-stable enterotoxin of Escherichia coli. However its physicochemical properties seem to be different from those of E. coli.