Development of a real-time PCR assay for detection and quantification of Francisella tularensis.

The facultative intracellular bacterium, Francisella tularensis, is an etiological agent of tularemia and is also considered to be a potential biological threat agent due to its extreme infectivity. We established a real-time PCR assay using the LightCycler (LC) system to detect a Francisella-specific sequence of the outer membrane protein (fopA) gene. Twenty-five F. tularensis strains including 16 Japanese isolates were subjected to this LC-PCR assay, and were tested positive, whereas Francisella philomiragia and other bacteria species did not show any specific fluorescent signal. A linear response was observed using F. tularensis genomic DNAs of between 20 fg and 2 ng, corresponding to 1.2 to 1.2 x 10(5) bacteria. The newly established real-time PCR allows the detection of the F. tularensis genome specifically, sensitively, and rapidly. This assay may contribute to the standardization of the laboratory diagnosis of tularemia.