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Virulence of Bacillus cereus: A multivariate analysis
Biological activity and presence of DNA sequences related to virulence genes were studied in 21 strains of the Bacillus cereus group. The activity of spent culture supernatants and the effect of infection by vegetative bacterial cells were assessed on cultured human enterocytes (Caco-2 cells). The e...
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Published in: | International journal of food microbiology 2007-05, Vol.116 (2), p.197-206 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Biological activity and presence of DNA sequences related to virulence genes were studied in 21 strains of the
Bacillus cereus group. The activity of spent culture supernatants and the effect of infection by vegetative bacterial cells were assessed on cultured human enterocytes (Caco-2 cells). The effect of extracellular factors on the detachment, necrosis and mitochondrial dehydrogenase activity of cultured human enterocytes was studied. Hemolytic activity on rabbit red blood cells was also evaluated and the effect of direct procaryotic–eucaryotic interactions was assessed in infection assays with vegetative bacterial cells.
Concerning virulence genes, presence of the DNA sequences corresponding to the genes
entS,
entFM,
nhe (
A,
B and
C),
sph,
hbl (
A,
B,
C and
D),
piplC and
bceT was assessed by PCR. Ribopatterns were determined by an automated riboprinting analysis after digestion of the DNA with
EcoRI. Principal component analysis and biplots were used to address the relationship between variables.
Results showed a wide range of biological activities: decrease in mitochondrial dehydrogenase activity, necrosis, cell detachment and hemolytic activity. These effects were strain-dependent. Concerning the occurrence of the DNA sequences tested, different patterns were found. In addition, ribotyping showed that strains under study grouped into two main clusters. One of these clusters includes all the strains that were positive for all the DNA sequences tested.
Positive and negative correlations between variables under study were evidenced. Interestingly, high detaching strains were positively correlated with the presence of the sequences
entS,
nheC and
sph. Within gene complexes, high correlation was found between sequences of the
hbl complex. In contrast, sequences of the
nhe complex were not correlated. Some strains clustered together in the biplots. These strains were positive for all the DNA sequences tested and they were able to detach enterocytes upon infection.
Our results highlight the multifactorial character of the virulence of the
B. cereus group and show the correlation between ribopatterns, occurrence of toxin genes and biological activity of the strains under study. |
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ISSN: | 0168-1605 1879-3460 |
DOI: | 10.1016/j.ijfoodmicro.2006.12.013 |