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The Effect of Spices on the Growth and Dectection of Salmonella and Shiga Toxin-producing Escherichia coli in a Primary Enrichment

Castelijn, Greetje; Lange, Lotte de; Voort, Menno van der

Résumé

Introduction: The first step of most detection methods for foodborne
pathogens is primary enrichment. The growth of foodborne pathogens
in primary enrichment can be influenced by the food product that is
present in the primary enrichment as well.
Purpose: The effect of 46 spices on the growth of Salmonella
and Shiga toxin-producing Escherichia coli (STEC) in a primary
enrichment was analyzed.
Methods: Salmonella and STEC were cultured in different primary
enrichment media in the presence of different spices. After incubation
of the primary enrichments for 18 h at 37°C, the growth of Salmonella
and STEC was evaluated by different isolation media and real-time
PCR.
Results: The results indicated that allspice, badiane, cinnamon,
clove, garlic, mustard seed, sesame, ginger and onion had an
antimicrobial effect on the growth of Salmonella and STEC in buffered
peptone water (BPW), which is the medium generally used for
primary enrichments as described in the ISO methods. Additionally,
allspice, badiane, cinnamon and clove also had an inhibitory effect
on real-time PCR used to screen enrichments for the presence
of Salmonella or STEC. Therefore several spices influenced the
Salmonella and STEC detection methods, resulting in false negative
results. Therefore we explored whether the antimicrobial effect of
the growth-inhibiting spices could be countered by replacing BPW
with tryptic soy broth (TSB), adding K2
SO3
, or increasing the dilution
factor of the spices in the primary enrichment. This revealed that
for most spices the growth inhibiting effect could be countered by
using TSB+K2
SO3
instead of BPW, or by increasing the dilution
factor. Furthermore, it was shown that the PCR-inhibiting compounds
originating from some spices could be removed by the use of
a different DNA extraction method, and that different PCR DNA
polymerases differ in their sensitivity to these components.
Significance: In conclusion, the results presented in this study can
be used to improve the detection methods for Salmonella and STEC
in the presence of spices.