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.
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.
Pierce
Carrie Y
CY
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, United States.
Barr
John R
JR
Woolfitt
Adrian R
AR
Moura
Hercules
H
Shaw
Edward I
EI
Thompson
Herbert A
HA
Massung
Robert F
RF
Fernandez
Facundo M
FM
D000818:Animals; D002417:Cattle; D016997:Coxiella burnetii / Q000145:classification / Q000302:isolation & purification*; D016002:Discriminant Analysis; D005843:Geography; D006801:Humans; D016018:Least-Squares Analysis; D015999:Multivariate Analysis; D010363:Pattern Recognition, Automated; D011778:Q Fever / Q000175:diagnosis; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization