The efficiency of a novel biomarker (the transcriptional regulator,
XRE
) was tested and evaluated in differentiating
Bacillus thuringiensis
from
Bacillus cereus
group species in environmental and spiked samples based on PCR and real-time PCR. Totally 120 strains, representing two bacterial groups,
B. cereus
group and non-
Bacillus
sp., were used to evaluate the performance of
XRE
and crystal protein (
cry
2, an existing biomarker). Further, three diverse samples (kimbap, lettuce, and spinach) were inoculated with
B. thuringiensis
and prominent biomarkers
XRE
and
cry
2 were used as targets. Direct analysis of the detection results for the pure cultures of
B. cereus
group wild-types, references and type strains revealed an accuracy rate of 97.5% targeting
XRE
, and 83.3% targeting
cry
2. The real-time PCR was constructed with a
R
2
-value of 0.993. For the artificially contaminated samples, a concentration of 10
3
CFU/g of
B. thuringiensis
in spiked food samples could be detected using real-time PCR targeting
XRE.
A good performance was obtained with
XRE
in discriminating
B. thuringiensis
from
B. cereus
groups, as well as detecting
B. thuringiensis
in spiked food samples with PCR or real-time PCR. Therefore, this real-time PCR targeting X
RE
can be used as a dependable and promising tool to identify
B. thuringiensis
in foods.
The aim of this study was to evaluate the microbiological quality and safety of fresh produce at retail level in Korea in order to periodically update information and establish available risks associated with consumption of fresh fruits and vegetables. The samples from different markets located in 3 provinces of South Korea were collected. The protocol in the Korean Food Standards Codex was applied and generic Escherichia coli, coliforms, aerobic mesophilic bacteria (AMB), and yeast and mold (YM) in 360 packaged and unpackaged fresh fruits and vegetables were analyzed. Presence of pathogens was examined using real-time polymerase chain reaction (q-PCR) after enrichment of samples. For all, the microbial counts ranged from 1.7 to 10.6 log cfu/g for AMB, 2.2 to 7.9 log cfu/g for coliforms, and 5.5 to 7.9 log cfu/g for YM. Three lettuce samples were contaminated by E. coli with a bacterial load ranging from 2 to 4 log cfu/g. Salmonella spp. were not detected in any fresh produce. Listeria monocytogenes, E. coli O157:H7, and Staphylococcus aureus were found in 1 (0.6%), 3 (0.8%), and 5 (1.4%) fresh produce samples, respectively. Bacillus cereus (50.3%) and Clostridium perfringens (13.3%) had the highest prevalence. These results indicate the need for employing strict control measures and developing preventive strategies to improve the quality and safety of fresh produce in Korea.
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