Of 40 ready-to-eat salads, 3 (7.5%) were positive for Clostridium diffi cile by PCR. Two isolates were PCR ribotype 017 (toxin A-, B+), and 1 was PCR ribotype 001. Isolates were susceptible to vancomycin and metronidazole but variably resistant to other antimicrobial drugs. Ready-to-eat salads may be potential sources for virulent C. diffi cile.

Aims:  To determine the incidence of emetic toxin producing Bacillus cereus in soil, animal faeces and selected vegetable produce to compare the results with the previously reported high incidence in rice paddy fields. To examine whether the emetic toxin has antibiotic activity. Methods and Results:  The incidence of emetic toxin producing B. cereus was evaluated by plating on selective agar 271 samples of soils, animal faeces, raw and processed vegetables. Overall, 45·8% of samples were positive for B. cereus. One hundred and seventy‐seven B. cereus isolates were recovered at 30°C with the grand mean spore count being 2·6 ± 1·7 log10 CFU g−1 and 148 B. cereus isolates were recovered at 7°C with the grand mean spore count being 2·2 ± 1·2 log10 CFU g−1 of the177 B. cereus isolated at 30°C, only 3 were positive for emetic toxin production at a titre of 1/64, 1/32, 1/16, respectively. Also, 1 of 148 B. cereus isolated at 7°C was positive for emetic toxin production to a titre of 1/128. All positive isolates came from washed or unwashed potato skins, one was psychrotrophic as determined by PCR and growth at 7°C on subculture. The emetic toxin was not shown to have any antibiotic effects in growth inhibition studies. Conclusions:  While B. cereus was a common isolate, the incidence of the emetic strain was rare. This is in contrast to previous findings of the high incidence in rice paddy fields and the processing environment, which may suggest rice is a selective area for growth of the emetic strain of B. cereus. Significance and Impact of Study:  The finding that a psychrotrophic isolate of B. cereus can produce emetic toxin is the first ever such observation and suggests the possibility that psychrotrophic isolates could grow in refrigerated fresh foods and cause emesis. The incidence of emetic B. cereus strains in rice paddy fields now requires further study for comparison with the low incidence found in other soils. The emetic toxin failed to inhibit the growth of other bacterial, fungal and yeast species. Whether the toxin (which is similar in structure to the antibiotic valinomycin) plays a competitive role in the environment therefore remains unclear.

Seven emetic toxin‐producing strains of Bacillus cereus were examined for toxin production in Skim Milk Medium at incubation temperatures ranging from 10 to 50 °C. Minimum and maximum growth temperatures were found to be 12 and 46 °C, respectively. At 12 and 15 °C, levels of toxin production were significantly higher (P < 0·01) than that observed at 30 °C, while no toxin was produced above 37 °C. Increased levels of sporulation were observed at increased temperatures, and no correlation was found between levels of sporulation and toxin production (R2 = 0·086).

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