Seven outbreaks of
Bacillus cereus food poisoning occurred in Osaka prefecture during the period from June 1973 to October 1978. All the outbreaks involved cookedorice, from which large numbers of
B. cereus were isolated. Six outbreaks were of “Vomiting type” with the characteristics symptoms of nausea and vomiting and an incubation period of between 0.5 and 4hr; the other one was of “Diarrheal type” with diarrhea and abdominal pain and an incubation period of 2 to 12hr.
Eighty-two samples of uncooked rice, 142 samples of cooked rice and 41 samples of “Sushi” were purchased from retail shops and caterers and examined for
B. cereus; 66% of the uncooked rice, 66% of the cooked rice and 42% of the “Sushi” were found to be contaminated with
B. cereus.
All 36 strains isolated from rice involved in the food poisoning failed to hydrolyze starch, whereas 38% of the strains isolated from cooked rice and 83% of those from uncooked rice did hydrolyze starch.
All the strains isolated from the outbreaks survived heat treatment at 90°C for 60min, at 100°C for 10 and 30min or at 105°C for 5min. Of the strains isolated from cooked rice, 97%, 70%, 39%, and 33% survived heating for 60min at 90°C, for 10min at 100°C, for 30min at 100°C, and for 5min at 105°C, respectively; of those isolated from uncooked rice, 93%, 26%, 10% and 5% survived heating for 60min at 90°C, for 10min at 100°C, for 30min at 100°C, and for 5min at 105°C, respectively.
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