Strain and phase identification of the U.S. category B agent Coxiella burnetii by matrix assisted laser desorption/ionization time-of-flight mass spectrometry and multivariate pattern recognition

• Published in: Analytica chimica acta 2007-01, Vol.583 (1), p.23-31
• Main Authors: Pierce, Carrie Y., Barr, John R., Woolfitt, Adrian R., Moura, Hercules, Shaw, Edward I., Thompson, Herbert A., Massung, Robert F., Fernandez, Facundo M.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Animals; Cattle; Chemistry; Coxiella burnetii; Coxiella burnetii - classification; Coxiella burnetii - isolation & purification; Discriminant Analysis; Exact sciences and technology; Geography; Humans; Least-Squares Analysis; Matrix-assisted laser desorption/ionization; Microorganism identification; Multivariate Analysis; Partial least squares discriminant analysis; Pattern Recognition, Automated; Q Fever - diagnosis; Species Specificity; Spectrometric and optical methods; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Time-of-flight mass spectrometry
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2006.09.065

Accurate bacterial identification is important in diagnosing disease and in microbial forensics. Coxiella burnetii, a highly infective microorganism causative of the human disease Q fever, is now considered a U.S. category B potential bioterrorism agent. We report here an approach for the confirmatory identification of C. burnetii at the strain level which involves the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and supervised pattern recognition via Partial Least Squares-Discriminant Analysis (PLS-DA). C. burnetii isolates investigated in this study included the following prototype strains from different geographical and/or historical origins and with different antigenic properties: Nine Mile I, Australian QD, M44, KAV, PAV, Henzerling, and Ohio. After culture and purification following standard protocols, linear MALDI-TOF mass spectra of pure bacterial cultures were acquired in positive ion mode. Mass spectral data were normalized, baseline-corrected, denoised, binarized and modeled by PLS-DA under crossvalidation conditions. Robustness with respect to uncontrolled variations in the sample preparation and MALDI analysis protocol was assessed by repeating the experiment on five different days spanning a period of 6 months. The method was validated by the prediction of unknown C. burnetii samples in an independent test set with 100% sensitivity and specificity for five out of six strain classes.