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البحوث المنشورة

البحث (1):

عنوان البحث:

Multilocus sequence typing of Cronobacter spp. from powdered infant formula and milk powder production factories

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تاريخ النشر:

02/01/2013

موجز عن البحث:

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

البحث (2):

عنوان البحث:

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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تاريخ النشر:

21/06/2014

موجز عن البحث:

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.

البحث (3):

عنوان البحث:

Diversity of the Cronobacter Genus as Revealed by Multilocus Sequence Typing

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تاريخ النشر:

September, 2012

موجز عن البحث:

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.

البحث (4):

عنوان البحث:

Comparative Analysis of Genome Sequences Covering the Seven Cronobacter Species

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تاريخ النشر:

16/11/2012

موجز عن البحث:

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.

المؤتمرات العلمية:

المؤتمر (1):

عنوان المؤتمر:

5th Congress of European Microbiologists

تاريخ الإنعقاد:

21/07/2013

مكان الإنعقاد:

Leipzig, Germany

طبيعة المشاركة:

Poster presentation

عنوان المشاركة:

Effect of desiccation and heat tolerance of Cronobacter sakazakii isolates from clinical and milk powder processing factories

ملخص المشاركة:

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.