A survey of dried mushrooms (Lentinula edodes (Shiitake) and Auricularia auricula (Wood Ear)) sourced
from China was carried out to determine the natural contamination of these mushrooms with spores of
proteolytic Clostridium botulinum and non-proteolytic C. botulinum. The mushrooms were collected
from supermarkets and retailers in 21 cities in China during October 2008. Spore loads of C. botulinum
in mushrooms have a degree of uncertainty and variability and this study contributes valuable data for
determining prevalence of spores of C. botulinum in mushrooms. An optimized detection protocol that
combined selective enrichment culture with multiplex PCR was used to test for spores of proteolytic
and non-proteolytic C. botulinum. Detection limits were calculated, using a maximum likelihood protocol,
from mushroom samples inoculated with defined numbers of spores of proteolytic C. botulinum or
non-proteolytic C. botulinum. Based on the maximum likelihood detection limit, it is estimated that
dried mushroom A. auricula contained b550 spores/kg of proteolytic C. botulinum, and b350 spores/kg
of non-proteolytic C. botulinum. Dried L. edodes contained b1500 spores/kg of proteolytic C. botulinum
and it was not possible to determine reliable detection limits for spores of non-proteolytic C. botulinum
using the current detection protoco