Identification of Francisella tularensis cluster in central and western Europe.
Bottom Line: We conducted a molecular analysis of Francisella tularensis strains isolated in Switzerland and identified a specific subpopulation belonging to a cluster of F. tularensis subsp. holarctica that is widely dispersed in central and western continental Europe.This subpopulation was present before the tularemia epidemics on the Iberian Peninsula.
Affiliation: University of Bern, Bern, Switzerland.
We conducted a molecular analysis of Francisella tularensis strains isolated in Switzerland and identified a specific subpopulation belonging to a cluster of F. tularensis subsp. holarctica that is widely dispersed in central and western continental Europe. This subpopulation was present before the tularemia epidemics on the Iberian Peninsula.
Related in: MedlinePlus
Mentions: Thirteen F. tularensis isolates collected over the past 10 years in Switzerland (Figure 1) were subjected to extensive genetic characterization. The species and subspecies designations of all strains were confirmed by real-time PCR that targeted the fopA gene and by amplification of the RD1 region (8), which showed that all strains were F. tularensis subsp. holarctica. A reference panel of 12 F. tularensis subsp. holarctica strains (7) and the genome sequence of the strain isolated in France, FTNF002 (GenBank accession no. NC_009749), were included in the study to represent the currently known genetic subpopulations within the subspecies. All strains from Switzerland were genetically characterized at 6 highly variable loci (by MLVA) and 14 more stable loci that indicate the classification F. tularensis subsp. holarctica strains into genetic subpopulations (by Ftind analysis) (3,6,7). The RD analysis was also performed because a 1.59-kb deletion marker, RD23, was reported to be restricted to strains from France and Spain (3). The MLVA markers (M3, M6, M20, M21, M22, and M24) and Ftind markers (Ftind 25–38) were amplified by PCR and then sequenced with an ABI Prism 3100 genetic analyzer (Applied Biosystems, Foster City, CA, USA) and the BigDye Terminator cycle sequencing kit (Applied Biosystems). DNA fragment sizes were calculated from the nucleotide sequences of the MLVA and Ftind markers and used to compare the isolates with previously analyzed strains from the United States, Japan, France, and Russia (3,7). The RD23 marker was assayed by using standard PCR and agarose gel methods as previously described (3). A cluster analysis based on the MLVA and indel size data was performed by using BioNumerics version 3.5 (Applied Maths, Kortrjik, Belgium).