Figure 2: Truncated Pathogenic Organism
a UVM broth may be used in the case
of the Listeria-like organism assay
b Fraser broth in the case of the
Listeria-like organism assay
c Modified Oxford Medium may be
used in the Listeria-like organism assay
d Differential assays for typical iso-
lates and confirmation steps not
and 4. “Listeria-like” microbes, for example, those that hydrolyze esculin in
Fraser broth (as shown by blackened
tubes) or typical black colonies on MOX
agar, could include Listeria spp., Entero-
coccus spp., Lactobacillus spp., among others.
6, 7 The finding of organisms within
the broad group of “esculin-hydrolyzing
bacteria” (i.e., “Listeria-like organisms”)
Figure 3: Blackened and Unblackened
Broths. Image Courtesy of ABC Research,
Figure 4: MOX Medium with Black Colonies
on a pre-operational surface indicates
that improvements in cleaning and sanitation are needed, but they do not directly indicate that the surface is
contaminated with a pathogen. Should a
pre-operational surface test negative,
such data would provide evidence that
the surface is free of selected Gram-positive microbes, including Listeria monocytogenes. Should such a surface test
positive, all implicated product lots
should be tested as appropriate for
Listeria in a statistically relevant manner in
accordance with the appropriate U.S.
Food and Drug Administration (FDA) or
U.S. Department of Agriculture (USDA)
guidance, and appropriate actions taken,
depending on the result. The presence of
L. monocytogenes would indicate an adulterated lot.
Frank et al.
8 showed that 85% of 47
Listeria spp.-positive environmental samples among 409 samples tested from 15
dairy plants recovered more than 6,600
lecithinase-positive, typical black
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