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

Abstract

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 FindingsWe 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/SignificanceThe 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.

Forensic Microbiology

“…The two Slovakian isolates clustered with the highly pathogenic laboratory strain Schu4. The isolate FSC198 was finally sequenced completely and found to be almost identical to the laboratory strain Schu4 (6). A comparison of mutation patterns of an isolate propagated from Schu4 in vitro (FSC043) and FSC198 indicated that FSC198 diverged from its progenitor Schu4 and has subsequently passed life-cycles in a natural environment (36).…”

Inferring genomic flux in bacteria

“…Individual feature gain events are represented by light gray arrows, and individual feature loss events are represented by black arrows. and two subsequent sequencing projects showed that it exhibits little genomic diversity (Beckstrom-Sternberg et al 2007;Chaudhuri et al 2007). Subspecies holarctica is a highly infectious but rarely fatal lineage (Ellis et al 2002), of which three strains have been sequenced (Petrosino et al 2006 Scheuermann, et al, unpubl.).…”

Mission oriented diagnostic real-time PCR

“…tularensis, die bei Bratislava in der Slowakei und im Südosten Ös-terreichs u.a. aus Zecken isoliert wurden, um Bakterien handelt, die mit dem Laborstamm Schu S4 aus den USA nahezu identisch sind und von ihm abstammen dürften [28]. Eine konkrete Erklärung dafür konnte nicht gegeben werden.…”