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مجال
التميز
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تميز دراسي و
بحثي
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البحوث المنشورة
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البحث (1):
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عنوان البحث:
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Multilocus
sequence typing of Cronobacter spp. from powdered infant formula and milk powder production
factories
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رابط إلى البحث:
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here
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تاريخ النشر:
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02/01/2013
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موجز عن البحث:
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This study applied the Cronobacter
spp. multilocus sequence typing (MLST) scheme to three strain collections,
then known as Enterobacter sakazakii, which had been
isolated between 1988 and 2009 from 14 countries. The results revealed the
predominance (85%) of Cronobacter sakazakii (72 strains) in
all three collections. The remaining strains were Cronobacter turicensis
(10%), Cronobacter malonaticus (4%), and Cronobacter
muytjensii (1%). No strains of Cronobacter dublinensis,
Cronobacter universalis or Cronobacter
condimenti were identified. Twenty-one out of seventy-two C. sakazakii
strains were in the clinically significant ST4 clonal complex, and were found
in all three strain collections. These results confirm C. sakazakii
ST4 is one of the predominant clonal complexes over the past 20 years in
several parts of the world. Further understanding of the ecosystem and
sources of the organism may be used for the development of improved
intervention strategies in the diary industry
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البحث (2):
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عنوان البحث:
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Genotypic
and phenotypic characteristics of Cronobacter species, with particular
attention to the newly reclassified species Cronobacter helveticus, Cronobacter
pulveris, and Cronobacter zurichensis
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رابط إلى البحث:
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Click
here
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تاريخ النشر:
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21/06/2014
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موجز عن البحث:
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In 2013, Enterobacter helveticus, Enterobacter pulveris and Enterobacter turicensis, were reclassified as Cronobacter helveticus, Cronobacter pulveris and Cronobacter zurichensis, respectively. Previously
these species had been used as negative controls for some Cronobacter detection assays. This study
examined cultural, biochemical and molecular Cronobacter detection and identification
assays, with emphasis on the new species. Additionally, 32 Cronobacter genomes were examined for the
presence of PCR target genes using the BLAST function of the online Cronobacter PubMLST facility. The results
of the cultural methods varied and no single medium was able to correctly
detect all Cronobacter spp. Since the supporting
databases have not been updated to include the Cronobacter genus, Enterobacter sakazakii was returned for four strains
of the newly reclassified species with ID32E and none with API 20E. PCR
probes targeting rpoB and ompA could not correctly identify
the new Cronobacter spp., due to primer
specificity or absent target genes. As neonates have been identified as a
high-risk group for infection, international standards require the absence of
all Cronobacter species in powdered infant
formula. However, many conventional detection methods cannot correctly
identify the newly recognized species. Conversely, DNA sequence-based methods
can adapt to taxonomic revisions and will likely become more common.
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البحث (3):
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عنوان البحث:
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Diversity
of the Cronobacter Genus as Revealed by Multilocus Sequence Typing
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رابط إلى البحث:
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Click
here
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تاريخ النشر:
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September, 2012
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موجز عن البحث:
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Cronobacter (previously
known as Enterobacter sakazakii) is a diverse bacterial genus consisting of
seven species: C. sakazakii, C. malonaticus, C. turicensis, C. universalis,
C. muytjensii, C. dublinensis, and C. condimenti. In this study, we have used
a multilocus sequence typing (MLST) approach employing the alleles of 7 genes
(atpD, fusA, glnS, gltB, gyrB, infB, and ppsA; total length, 3,036 bp) to
investigate the phylogenetic relationship of 325 Cronobacter species
isolates. Strains were chosen on the basis of their species, geographic and
temporal distribution, source, and clinical outcome. The earliest strain was
isolated from milk powder in 1950, and the earliest clinical strain was
isolated in 1953. The existence of seven species was supported by MLST.
Intraspecific variation ranged from low diversity in C. sakazakii to
extensive diversity within some species, such as C. muytjensii and C.
dublinensis, including evidence of gene conversion between species. The predominant
species from clinical sources was found to be C. sakazakii. C. sakazakii
sequence type 4 (ST4) was the predominant sequence type of cerebral spinal
fluid isolates from cases of meningitis.
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البحث (4):
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عنوان البحث:
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Comparative
Analysis of Genome Sequences Covering the Seven Cronobacter Species
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رابط إلى البحث:
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Click
here
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تاريخ النشر:
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16/11/2012
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موجز عن البحث:
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Background: Species of
Cronobacter are widespread in the environment and are occasional food-borne
pathogens associated with serious neonatal diseases, including bacteraemia,
meningitis, and necrotising enterocolitis. The genus is composed of seven
species: C. sakazakii, C. malonaticus, C. turicensis, C. dublinensis, C.
muytjensii, C. universalis, and C.condimenti. Clinical cases are associated
with three species, C. malonaticus, C. turicensis and, in particular, with C.
sakazakii multilocus sequence type 4. Thus, it is plausible that virulence
determinants have evolved in certain lineages.
Methodology/Principal Findings:
We generated high quality sequence drafts for eleven Cronobacter genomes
representing the seven Cronobacter species, including an ST4 strain of C.
sakazakii. Comparative analysis of these genomes together with the two
publicly available genomes revealed Cronobacter has over 6,000 genes in one
or more strains and over 2,000 genes shared by all Cronobacter. Considerable
variation in the presence of traits such as type six secretion systems, metal resistance (tellurite, copper
and silver), and adhesins were found. C. sakazakii is unique in the
Cronobacter genus in encoding genes enabling the utilization of exogenous
sialic acid which may have clinical significance. The C. sakazakii ST4 strain
701 contained additional genes as compared to other C. sakazakii but none of
them were known specific virulencerelated genes.
Conclusions/Significance:
Genome comparison revealed that pair-wise DNA sequence identity varies
between 89 and 97% in the seven Cronobacter species, and also suggested
various degrees of divergence. Sets of universal core genes and accessory genes unique to each
strain were identified. These gene sequences can be used for designing
genus/species specific detection assays. Genes encoding adhesins, T6SS, and
metal resistance genes as well as prophages are found in only subsets of
genomes and have contributed considerably to the variation of genomic
content. Differences in gene content likely contribute to differences in the
clinical and environmental distribution of species and sequence types.
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المؤتمرات العلمية:
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المؤتمر (1):
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عنوان المؤتمر:
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5th Congress of European Microbiologists
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تاريخ الإنعقاد:
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21/07/2013
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مكان
الإنعقاد:
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Leipzig, Germany
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طبيعة المشاركة:
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Poster presentation
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عنوان المشاركة:
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Effect of desiccation and heat
tolerance of Cronobacter sakazakii isolates from clinical and milk powder processing
factories
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ملخص المشاركة:
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Background:
Cronobacter (previously
Enterobacter sakazakii) is an opportunistic pathogen associated with human
infections, septicaemia and necrotizing enterocolitis and neonatal
meningitis. A 7 loci MLST scheme has been developed for Cronobacter which
revealed a strong association of clonal complex 4 with neonatal meningitis.
Previous studies
indicate that Cronobacter have the ability to survive desiccation conditions
for up to two years. These traits may play fundamental roles in its survival
in dried products, infant formula and factory environments . The desiccation
resistance genes have been found in
all Cronobacter species. A recent
study showed that the presence of
thermo tolerance genes in clinical isolates of C. sakazakii. The
study was aimed to investigate the
desiccation and thermo tolerance
of C. sakazakii strains
isolated clinical samples and PIF processing plants in order to understand
the persistence of this bacteria in different environments.
Methods:
The study was performed
to determine the bacterial heat tolerance of 13 C. sakazakii strains by
exposing them to different temperatures for different time intervals, after
being desiccated overnight.
Results:
The comparison of the
desiccated cells before and after exposure to dry heat has demonstrated
a high tolerance to a 60 min exposure
to dry heat than 30 minutes with little significant change in the
viable counts. Compared to non-desiccated cells, the desiccated cells after
heat treatment remained viable at high temperature even though the cell count
was reduced significantly.
Conclusion:
The results of this
study revealed that desiccation induces thermo tolerance in C. sakazakii indicating the limitations
of current physical treatments used by the food production factories to
inactivate food-borne pathogens thereby increasing the risk of
post-pasteurization contamination of the finished product increase, as found
in the strains isolated from milk powder factories in Germany.
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