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. 2007 Apr 4;2(4):e352.
doi: 10.1371/journal.pone.0000352.

Genome Sequencing Shows That European Isolates of Francisella Tularensis Subspecies Tularensis Are Almost Identical to US Laboratory Strain Schu S4

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Genome Sequencing Shows That European Isolates of Francisella Tularensis Subspecies Tularensis Are Almost Identical to US Laboratory Strain Schu S4

Roy R Chaudhuri et al. PLoS One. .
Free PMC article


Background: Francisella tularensis causes tularaemia, a life-threatening zoonosis, and has potential as a biowarfare agent. F. tularensis subsp. tularensis, which causes the most severe form of tularaemia, is usually confined to North America. However, a handful of isolates from this subspecies was obtained in the 1980s from ticks and mites from Slovakia and Austria. Our aim was to uncover the origins of these enigmatic European isolates.

Methodology/principal findings: We determined the complete genome sequence of FSC198, a European isolate of F. tularensis subsp. tularensis, by whole-genome shotgun sequencing and compared it to that of the North American laboratory strain Schu S4. Apparent differences between the two genomes were resolved by re-sequencing discrepant loci in both strains. We found that the genome of FSC198 is almost identical to that of Schu S4, with only eight SNPs and three VNTR differences between the two sequences. Sequencing of these loci in two other European isolates of F. tularensis subsp. tularensis confirmed that all three European isolates are also closely related to, but distinct from Schu S4.

Conclusions/significance: The data presented here suggest that the Schu S4 laboratory strain is the most likely source of the European isolates of F. tularensis subsp. tularensis and indicate that anthropogenic activities, such as movement of strains or animal vectors, account for the presence of these isolates in Europe. Given the highly pathogenic nature of this subspecies, the possibility that it has become established wild in the heartland of Europe carries significant public health implications.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Circular representation of the complete genome sequence of FSC198.
Predicted coding sequences are colored according to their GC content. The inner circle indicates the positions of SNPs (red) and VNTR differences (blue) relative to the published Schu S4 genome sequence. SNP and VNTR loci are numbered as in table 1.

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