Optimized MALDI TOF Mass Spectrometry Identification ofFrancisella tularensisSubsp. holarctica

Francisella tularensisis a tier 1 agent causing the zoonosis tularemia. This highly infectious Gram-negative bacterium is occasionally isolated from human samples (especially blood samples) in routine clinical microbiology laboratories. A rapid and accurate method for identifying this pathogen is needed in order to optimize the infected patient's healthcare management and prevent contamination of the laboratory personnel. MALDI TOF mass spectrometry has become the gold standard for the rapid identification of most human pathogens. However,F. tularensisidentification using such technology and commercially available databases is currently considered unreliable. Real-time PCR-based methods for rapid detection and accurate identification ofF. tularensisare not available in many laboratories. As a national reference center for tularemia, we developed a MALDI TOF database allowing accurate identification of the speciesF. tularensisand its differentiation from the closely related neighbor speciesF. tularensissubsp.novicidaandF. philomiragia. The sensitivity and specificity of this database were validated by testing 71F. tularensis strainsand 165 strains from 63 species not belonging to theFrancisellagenus. We obtained accurate identification at the species level and differentiation of all the tested bacterial strains. In particular,F. tularensiscould be accurately differentiated from other small Gram-negative bacilli occasionally isolated from human samples, including species of the HACEK group andBrucella melitensis.