An immunoaffinity tandem mass spectrometry (iMALDI) assay for detection of Francisella tularensis.

Francisella tularensis (F. tularensis) has been designated by the CDC as 1 of the 10 organisms most likely to be engineered for bioterrorism. Symptoms of tularemia in humans are non-specific, thus making the disease difficult to diagnose. If not quickly diagnosed and treated, the disease has a high mortality rate--thus methods for early and specific diagnosis are of critical importance. This immunoaffinity MALDI MS/MS (iMALDI) assay provides unambiguous detection of F. tularensis peptides at attomole levels from peptide solutions, and at low CFU levels from bacteria. The addition of stable-labeled versions of the peptide as internal standards allows absolute quantitation of F. tularensis peptides with a linear dynamic range spanning two orders of magnitude. The ability of mass spectrometry to obtain amino acid sequence data on affinity-captured peptides provides absolute specificity and avoids "false positives" from the non-specific binding. The F. tularensis iMALDI assay has been applied to different samples, such as nasal swabs. This novel quantitative diagnostic F. tularensis iMALDI assay allows the safe, sensitive, and specific detection of F. tularensis. The assay can be easily adapted to other target peptides and therefore has broad application potential in clinical diagnosis of other pathogens and diseases.