The LOD for the presence of proteolytic C. botulinum and nonproteolytic
C. botulinum in A. auricular was 550 and 350 spores/kg
(Table 3). The LOD for the presence of proteolytic C. botulinum in
L. edodes was 1500 spores/kg. All IAC were positive indicating that all
the PCR reactions had been successful. The failure to detect proteolytic
C. botulinum and non-proteolytic C. botulinum in some LOD samples
may be due to a combination of inhibitory factors and/or bacteria in
the dried mushroom samples. In the LOD samples containing L. edodes,
there was no observable microbial growth i.e. no gas formation or signs
of turbidity, in the original enrichment cultureswhen bottleswere incubated
at 12 °C to detect non-proteolytic C. botulinum (all LOD samples
tested negative for non-proteolytic C. botulinum, results not shown).
However when enriching for proteolytic C. botulinum at 35 °C gas was
formed and all the enrichment cultures became turbid. Although proteolytic
C. botulinum was not detected in some of the enrichment cultures,
microscopic examination revealed the presence of other spore
forming bacteria.