Abstract
Francisella tularensis is 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. tularensis identification using such technology and commercially available databases is currently considered unreliable. Real-time PCR-based methods for rapid detection and accurate identification of F. tularensis are not available in many laboratories. As a national reference center for tularemia, we developed a MALDI TOF database allowing accurate identification of the species F. tularensis and its differentiation from the closely related neighbor species F. tularensis subsp. novicida and F. philomiragia. The sensitivity and specificity of this database were validated by testing 71 F. tularensis strains and 165 strains from 63 species not belonging to the Francisella genus. We obtained accurate identification at the species level and differentiation of all the tested bacterial strains. In particular, F. tularensis could be accurately differentiated from other small Gram-negative bacilli occasionally isolated from human samples, including species of the HACEK group and Brucella melitensis.
Highlights
Tularemia is a zoonosis classically caused by Francisella tularensis [1]
The same result was obtained after exposure of bacterial suspensions to 75% ethanol, 70% formic acid, and acetonitrile, which corresponded to the entire process usually recommended by Bruker Daltonics ® (Wissembourg, France) for the inactivation of bacteria before MALDI TOF ms analysis
Bacterial strains sent to our FNRCT for expertise have usually been grown on Choco-PVX plates, which are rich media widely used for fastidious growth and difficult-to-identify bacteria
Summary
Tularemia is a zoonosis classically caused by Francisella tularensis [1]. F. tularensis contains four subspecies, of which only two are etiological agents of tularemia: F. tularensis subsp. Tularensis (type A) in North America and F. tularensis subsp. Type A strains are classified as category A of the CDC’s biological threat agents (Centers for Diseases Control and Prevention, Atlanta, USA) [2,3]. Type B strains have recently been detected in Southern Australia [4]. Mediasiatica is restricted to Central Asia and Russia but has never been isolated in humans [5]. Novicida is a waterborne bacterium occasionally associated with human infections [6]. Human tularemia cases are most often sporadic.
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