Sensitive Detection of Francisella tularensis Directly from Whole Blood by Use of the GeneXpert System
ABSTRACTFrancisella tularensisis a potential bioterrorism agent that is highly infectious at very low doses. Diagnosis of tularemia by blood culture and nucleic acid-based diagnostic tests is insufficiently sensitive. Here, we demonstrate a highly sensitiveF. tularensisassay that incorporates sample processing and detection into a single cartridge suitable for point-of-care detection. The assay limit of detection (LOD) and dynamic range were determined in a filter-based cartridge run on the GeneXpert system.F. tularensisDNA in buffer or CFU ofF. tularensiswas spiked into human or macaque blood. To simulate detection in human disease, the assay was tested on blood drawn from macaques infected withF. tularensisSchu S4 at daily intervals. Assay detection was compared to that with a conventional quantitative PCR (qPCR) assay and blood culture. The assay LOD was 0.1 genome equivalents (GE) per reaction and 10 CFU/mlF. tularensisin both human and macaque blood. In infected macaques, the assay detectedF. tularensison days 1 to 4 postinfection in 21%, 17%, 60%, and 83% of macaques, respectively, compared to conventional qPCR positivity rates of 0%, 0%, 30%, and 100% and CFU detection of blood culture at 0%, 0%, 0%, and 10% positive, respectively. Assay specificity was 100%. The new cartridge-based assay can rapidly detectF. tularensisin bloodstream infections directly in whole blood at the early stages of infection with a sensitivity that is superior to that of other methods. The simplicity of the automated testing procedures may make this test suitable for rapid point-of-care detection.