There are claims Australian beef imports could be linked to E. coli outbreaks in Japan.
The Japanese authorities are looking into two outbreaks, one of which has killed four people since April.
The E coli is of a different type to that which has killed 18 people in an outbreak Europe.
Both outbreaks in Japan of the O157 strain E. coli are linked to Korean-style barbecue restaurants.
In the latest, the operator has apologised and says it suspects the infections might have been caused by beef from Australia.
However a public health inspection of the affected restaurant did not find E. coli bacteria.
Twenty people experienced moderate symptoms and have recovered, officials said, adding that the diners probably used the same chopsticks to cook raw meat slices and to eat them.
In the first outbreak, at another change, four people died after eating raw beef at a restaurant chain.