IDENTIFICATION AND CLASSIFICATION OF DIFFERENT ISOLATES OF FRANCISELLA-TULARENSIS

The causative agent of tularemia, Francisella tularenris, occurs in tw o main biovars, the highly virulent F. t. biovar tularensis, found in North America; and the less virulent biovar palaearctica, found all ov er the northern hemisphere. Two other biovars have been proposed, F. t . biovar mediaasiatica and F. t. biovar palaearctica var. japonica. In Sweden tularemia is most frequently observed in man and varying hares (Lepus timidus), and occasionally in other species. Tularemia in hare s is normally an acute fatal disease, although less fatal infections h ave been reported. The diagnosis of tularemia is routinely based on im munological reactions. We studied 10 different isolates of F. tularens is from varying hares, one isolate from an Ural owl (Strix urralensis) , one vaccine strain, one strain of F. t. biovar japonica, and six iso lates from a virulence study of F. tularensis, by biochemical tests an d by hybridization experiments with probes complementary to 16S rRNA. Air isolates, except the isolate F. t. biovar japonica, were character ized as F. t. biovar palaearctica by biochemical tests. In the 16S rRN A analysis all isolates were positive to the probe for Francisella tul arensis and the probe for F. t. biovar palaearctica with the exception that F. t. biovar japonica reacted with the probe specific to F. t. b iovar tularensis. To further confirm that the strains used belonged to F. t. biovar palaearctica virulence rests in rabbits were performed w hich disclosed this phenotype. The results presented in this work show that the isolated strains from the western part of Europe were F. t. biovar palaearctica, irrespective of animal origin or virulence.