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PLoS One. 2009;4(3):e4829. doi: 10.1371/journal.pone.0004829. Epub 2009 Mar 16.

Evidence that plasmid-borne botulinum neurotoxin type B genes are widespread among Clostridium botulinum serotype B strains.

Author information

1
Department of Food Safety and Veterinary Public Health, Unit of Microorganisms and Food Technologies, Istituto Superiore di Sanità, Rome, Italy. giovanna.franciosa@iss.it

Abstract

BACKGROUND:

Plasmids that encode certain subtypes of the botulinum neurotoxin type B have recently been detected in some Clostridium botulinum strains. The objective of the present study was to investigate the frequency with which plasmid carriage of the botulinum neurotoxin type B gene (bont/B) occurs in strains of C. botulinum type B, Ab, and A(B), and whether plasmid carriage is bont/B subtype-related.

METHODOLOGY/PRINCIPAL FINDINGS:

PCR-Restriction fragment length polymorphism was employed to identify subtypes of the bont/B gene. Pulsed-field gel electrophoresis and Southern blot hybridization with specific probes were performed to analyze the genomic location of the bont/B subtype genes. All five known bont/B subtype genes were detected among the strains; the most frequently detected subtype genes were bont/B1 and /B2. Surprisingly, the bont/B subtype gene was shown to be plasmid-borne in >50% of the total strains. The same bont/B subtype gene was associated with the chromosome in some strains, whereas it was associated with a plasmid in others. All five known bont/B subtype genes were in some cases found to reside on plasmids, though with varying frequency (e.g., most of the bont/B1 subtype genes were located on plasmids, whereas all but one of the bont/B2 subtypes were chromosomally-located). Three bivalent isolates carried both bont/A and /B genes on the same plasmid. The plasmids carrying the bont gene were five different sizes, ranging from approximately 55 kb to approximately 245 kb.

CONCLUSIONS/SIGNIFICANCE:

The unexpected finding of the widespread distribution of plasmids harboring the bont/B gene among C. botulinum serotype B strains provides a chance to examine their contribution to the dissemination of the bont genes among heterogeneous clostridia, with potential implications on issues related to pathogenesis and food safety.

PMID:
19287483
PMCID:
PMC2653641
DOI:
10.1371/journal.pone.0004829
[Indexed for MEDLINE]
Free PMC Article

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