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Efficacy of allyl isothiocyanate in killing enterohemorrhagic Escherichia
coli O157:H7 on alfalfa seeds
2000 May 25
Int. J. Food Microbiol.
56:13-20. Park, C. M., P. J. Taormina, and L. R. Beuchat. 2000.
Center for Food Safety and
Quality Enhancement, Department of Food Science and Technology,
University
of Georgia,
Griffin 30223-1797, USA.
Volatile compounds occurring in the essential oil of plants were tested for
their efficacy in killing Escherichia coli O157:H7. Experiments using an agar
disk assay revealed that exposure of the pathogen to 50 microl of eugenol,
carvacrol, linalool, or methyl jasmonate in a 950-cc jar at 20, 37 or 47 degrees
C for up to 48 h failed to inhibit colony formation. However, exposure to 8
microl of allyl isothiocyanate (AIT) (equivalent to 8.4 ppm in the air within
the jar, if completely volatilized) resulted in more than a 7-log10 reduction in
population of E. coli O157:H7 at 37 degrees C within 48 h; significant (P < or =
0.05) reduction in populations also occurred in the presence of 4 microl of AIT
compared to 2 microl, which had no lethal affect. At 20 degrees C, the lethality
of AIT was substantially less, although significant reduction occurred when
disks were exposed to 8 or 10 microl of AIT compared to 4 or 6 microl and when
exposed to 4 or 6 microl compared to 2 microl. Treatment with 10 microl of AIT
for 5 h at 47 degrees C resulted in death of 6 log10 of E. coli O157:H7. The
efficacy of AIT in killing E. coli O157:H7 on dry and wet alfalfa seeds was
investigated. The pathogen, at an initial population of 2.7 log10 cfu/g of seed,
was not recovered by direct plating (< 0.7 log10 cfu/g) or enrichment of wet
seeds exposed to 50 microl of AIT/950-cc jar for 24 h at 37 or 47 degrees C.
Exposure of dry seeds containing 2.9 log10 cfu of E. coli O157:H7 per g to an
atmosphere containing 100 microl of AIT/950-cc jar (ca. 105 ppm AIT if
completely volatilized) for 24 h at 47 degrees C did not eliminate viable E.
coli O157:H7 cells. Unfortunately, the enhanced effectiveness of AIT in killing
the pathogen on wet alfalfa seeds is offset by a dramatic reduction in seed
viability. Nevertheless, the use of AIT as an alternative to chlorine for the
purpose of killing E. coli O157:H7 and perhaps other pathogens on alfalfa seed
holds promise. Factors that may influence conditions rendering increased
sensitivity of E. coli O157:H7 to AIT without compromising seed viability should
be investigated.
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