Highly Efficient Classification and Identification of Human Pathogenic Bacteria by MALDI-TOF MS

Accurate and rapid identification of pathogenic microorganisms is of critical importance in disease treatment and public health. Conventional work flows are time-consuming, and procedures are multifaceted. MS can be an alternative but is limited by low efficiency for amino acid sequencing as well as low reproducibility for spectrum fingerprinting. We systematically analyzed the feasibility of applying MS for rapid and accurate bacterial identification. Directly applying bacterial colonies without further protein extraction to MALDI-TOF MS analysis revealed rich peak contents and high reproducibility. The MS spectra derived from 57 isolates comprising six human pathogenic bacterial species were analyzed using both unsupervised hierarchical clustering and supervised model construction via the Genetic Algorithm. Hierarchical clustering analysis categorized the spectra into six groups precisely corresponding to the six bacterial species. Precise classification was also maintained in an independently prepared set of bacteria even when the numbers of m/z values were reduced to six. In parallel, classification models were constructed via Genetic Algorithm analysis. A model containing 18 m/z values accurately classified independently prepared bacteria and identified those species originally not used for model construction. Moreover bacteria fewer than 104 cells and different species in bacterial mixtures were identified using the classification model approach. In conclusion, the application of MALDI-TOF MS in combination with a suitable model construction provides a highly accurate method for bacterial classification and identification. The approach can identify bacteria with low abundance even in mixed flora, suggesting that a rapid and accurate bacterial identification using MS techniques even before culture can be attained in the near future. Accurate and rapid identification of pathogenic microorganisms is of critical importance in disease treatment and public health. Conventional work flows are time-consuming, and procedures are multifaceted. MS can be an alternative but is limited by low efficiency for amino acid sequencing as well as low reproducibility for spectrum fingerprinting. We systematically analyzed the feasibility of applying MS for rapid and accurate bacterial identification. Directly applying bacterial colonies without further protein extraction to MALDI-TOF MS analysis revealed rich peak contents and high reproducibility. The MS spectra derived from 57 isolates comprising six human pathogenic bacterial species were analyzed using both unsupervised hierarchical clustering and supervised model construction via the Genetic Algorithm. Hierarchical clustering analysis categorized the spectra into six groups precisely corresponding to the six bacterial species. Precise classification was also maintained in an independently prepared set of bacteria even when the numbers of m/z values were reduced to six. In parallel, classification models were constructed via Genetic Algorithm analysis. A model containing 18 m/z values accurately classified independently prepared bacteria and identified those species originally not used for model construction. Moreover bacteria fewer than 104 cells and different species in bacterial mixtures were identified using the classification model approach. In conclusion, the application of MALDI-TOF MS in combination with a suitable model construction provides a highly accurate method for bacterial classification and identification. The approach can identify bacteria with low abundance even in mixed flora, suggesting that a rapid and accurate bacterial identification using MS techniques even before culture can be attained in the near future. Currently the most popular methods for bacterial identification are based on microbiologic procedures, antibody recognition, and PCR amplification. Traditionally microbiologic methods are culture-based assays that examine the presence of bacterial species. These methods provide high sensitivity and specificity, but their efficiency is limited by the complexity of the procedures, including culture, selection, isolation, and morphologic and biochemical characterization, which usually take 48 h or longer. Serologic methods are presumptive and confined to the availability of antibodies and to bacteria that are included ahead in the assays. Molecular biology techniques, particularly PCR, have been regarded as non-culture-based methods with high efficiency and specificity (1Pershing D.H. Tenover F.C. Versalovic J. Tang Y.W. Unger E.R. Relman D.A. White T.J. Molecular Microbiology: Diagnostic Principles and Practice. American Society for Microbiology, Washington, D. C.2003Google Scholar). However, they are completely dependent on the known genetic sequences of the target bacteria. MS with its capability of de novo protein/peptide sequencing (such as electrospray ionization or MALDI-TOF MS for tandem MS/MS) or its high efficiency for proteome profiling (particularly MALDI-TOF MS) has been suggested as an alternative for microbial identification (2Anhalt J.P. Fenselau C. Identification of bacteria using mass spectrometry.Anal. Chem. 1975; 47: 219-225Crossref Scopus (382) Google Scholar, 3Athalye M. Noble W.C. Mallet A.I. Minnikin D.E. Gas chromatography-mass spectrometry of mycolic acids as a tool in the identification of medically important coryneform bacteria.J. Gen. Microbiol. 1984; 130: 513-519PubMed Google Scholar, 4Heller D.N. Cotter R.J. Fenselau C. Uy O.M. Profiling of bacteria by fast atom bombardment mass spectrometry.Anal. Chem. 1987; 59: 2806-2809Crossref PubMed Scopus (138) Google Scholar, 5Snyder A.P. McClennen W.H. Dworzanski J.P. Meuzelaar H.L. Characterization of underivatized lipid biomarkers from microorganisms with pyrolysis short-column gas chromatography/ion trap mass spectrometry.Anal. Chem. 1990; 62: 2565-2573Crossref PubMed Scopus (33) Google Scholar, 6Lay Jr., J.O. MALDI-TOF mass spectrometry of bacteria.Mass. Spectrom. Rev. 2001; 20: 172-194Crossref PubMed Scopus (447) Google Scholar, 7Dworzanski J.P. Snyder A.P. Classification and identification of bacteria using mass spectrometry-based proteomics.Expert Rev. Proteomics. 2005; 2: 863-878Crossref PubMed Scopus (56) Google Scholar). In the past decade, extraction of bacterial proteins for sequencing using tandem MS/MS (8Demirev P.A. Ho Y.P. Ryzhov V. Fenselau C. Microorganism identification by mass spectrometry and protein database searches.Anal. Chem. 1999; 71: 2732-2738Crossref PubMed Scopus (281) Google Scholar, 9Demirev P.A. Ramirez J. Fenselau C. Tandem mass spectrometry of intact proteins for characterization of biomarkers from Bacillus cereus T spores.Anal. Chem. 2001; 73: 5725-5731Crossref PubMed Scopus (90) Google Scholar, 10Warscheid B. Fenselau C. A targeted proteomics approach to the rapid identification of bacterial cell mixtures by matrix-assisted laser desorption/ionization mass spectrometry.Proteomics. 2004; 4: 2877-2892Crossref PubMed Scopus (64) Google Scholar, 11Pribil P.A. Patton E. Black G. Doroshenko V. Fenselau C. Rapid characterization of Bacillus spores targeting species-unique peptides produced with an atmospheric pressure matrix-assisted laser desorption/ionization source.J. Mass Spectrom. 2005; 40: 464-474Crossref PubMed Scopus (48) Google Scholar) or for proteome profiling followed by matching MS spectrum results to databases (fingerprinting) have been used for bacterial identification (6Lay Jr., J.O. MALDI-TOF mass spectrometry of bacteria.Mass. Spectrom. Rev. 2001; 20: 172-194Crossref PubMed Scopus (447) Google Scholar, 8Demirev P.A. Ho Y.P. Ryzhov V. Fenselau C. Microorganism identification by mass spectrometry and protein database searches.Anal. Chem. 1999; 71: 2732-2738Crossref PubMed Scopus (281) Google Scholar, 12Arnold R.J. Reilly J.P. Fingerprint matching of E. coli species with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of whole cells using a modified correlation approach.Rapid Commun. Mass Spectrom. 1998; 12: 630-636Crossref PubMed Google Scholar, 13Liang X. Zheng K. Qian M.G. Lubman D.M. Determination of bacterial protein profiles by matrix-assisted laser desorption/ionization mass spectrometry with high-performance liquid chromatography.Rapid Commun. Mass Spectrom. 1996; 10: 1219-1226Crossref PubMed Scopus (72) Google Scholar, 14Hathout Y. Demirev P.A. Ho Y.P. Bundy J.L. Ryzhov V. Sapp L. Stutler J. Jackman J. Fenselau C. Identification of Bacillus spores by matrix-assisted laser desorption ionization-mass spectrometry.Appl. Environ. Microbiol. 1999; 65: 4313-4319Crossref PubMed Google Scholar, 15Saenz A.J. Petersen C.E. Valentine N.B. Gantt S.L. Jarman K.H. Kingsley M.T. Wahl K.L. Reproducibility of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for replicate bacterial culture analysis.Rapid. Commun. Mass Spectrom. 1999; 13: 1580-1585Crossref PubMed Scopus (114) Google Scholar). Despite much improvement (10Warscheid B. Fenselau C. A targeted proteomics approach to the rapid identification of bacterial cell mixtures by matrix-assisted laser desorption/ionization mass spectrometry.Proteomics. 2004; 4: 2877-2892Crossref PubMed Scopus (64) Google Scholar, 11Pribil P.A. Patton E. Black G. Doroshenko V. Fenselau C. Rapid characterization of Bacillus spores targeting species-unique peptides produced with an atmospheric pressure matrix-assisted laser desorption/ionization source.J. Mass Spectrom. 2005; 40: 464-474Crossref PubMed Scopus (48) Google Scholar, 16Wang Z. Russon L. Li L. Roser D.C. Long S.R. Investigation of spectral reproducibility in direct analysis of bacteria proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Rapid Commun. Mass Spectrom. 1998; 12: 456-464Crossref PubMed Scopus (196) Google Scholar, 17Yao Z.P. Afonso C. Fenselau C. Rapid microorganism identification with on-slide proteolytic digestion followed by matrix-assisted laser desorption/ionization tandem mass spectrometry and database searching.Rapid Commun. Mass Spectrom. 2002; 16: 1953-1956Crossref PubMed Scopus (47) Google Scholar, 18Pineda F.J. Antoine M.D. Demirev P.A. Feldman A.B. Jackman J. Longenecker M. Lin J.S. Microorganism identification by matrix-assisted laser/desorption ionization mass spectrometry and model-derived ribosomal protein biomarkers.Anal. Chem. 2003; 75: 3817-3822Crossref PubMed Scopus (116) Google Scholar, 19Fox A. Mass spectrometry for species or strain identification after culture or without culture: past, present, and future.J. Clin. Microbiol. 2006; 44: 2677-2680Crossref PubMed Scopus (69) Google Scholar, 20Dworzanski J.P. Deshpande S.V. Chen R. Jabbour R.E. Snyder A.P. Wick C.H. Li L. Mass spectrometry-based proteomics combined with bioinformatic tools for bacterial classification.J. Proteome Res. 2006; 5: 76-87Crossref PubMed Scopus (64) Google Scholar), neither de novo amino acid sequencing nor protein fingerprinting has been applied to clinical or epidemiologic uses because they are relatively time-consuming and technique-demanding or have low reproducibility (16Wang Z. Russon L. Li L. Roser D.C. Long S.R. Investigation of spectral reproducibility in direct analysis of bacteria proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Rapid Commun. Mass Spectrom. 1998; 12: 456-464Crossref PubMed Scopus (196) Google Scholar, 19Fox A. Mass spectrometry for species or strain identification after culture or without culture: past, present, and future.J. Clin. Microbiol. 2006; 44: 2677-2680Crossref PubMed Scopus (69) Google Scholar). Further evaluation of the feasibility of applying MALDI-TOF MS for rapid and accurate microorganism identification is warranted. In this study, we systematically evaluated procedures for the rapid profiling and data analysis for bacterial classification and identification. We aimed to demonstrate that directly subjecting intact bacterial colonies for protein profiling using MALDI-TOF MS can be a simple and reliable approach (21Claydon M.A. Davey S.N. Edwards-Jones V. Gordon D.B. The rapid identification of intact microorganisms using mass spectrometry.Nat. Biotechnol. 1996; 14: 1584-1586Crossref PubMed Scopus (496) Google Scholar, 22Fenselau C. Demirev P.A. Characterization of intact microorganisms by MALDI mass spectrometry.Mass Spectrom. Rev. 2001; 20: 157-171Crossref PubMed Scopus (702) Google Scholar, 23Bright J.J. Claydon M.A. Soufian M. Gordon D.B. Rapid typing of bacteria using matrix-assisted laser desorption ionisation time-of-flight mass spectrometry and pattern recognition software.J. Microbiol. Methods. 2002; 48: 127-138Crossref PubMed Scopus (127) Google Scholar, 24Keys C.J. Dare D.J. Sutton H. Wells G. Lunt M. McKenna T. McDowall M. Shah H.N. Compilation of a MALDI-TOF mass spectral database for the rapid screening and characterisation of bacteria implicated in human infectious diseases.Infect. Genet. Evol. 2004; 4: PubMed Scopus Google Scholar, Y. J.P. D.N. of intact the strain a combined MALDI-TOF MS and 2006; PubMed Scopus Google Scholar, M. J. D. Tang J. Identification of by matrix-assisted laser desorption mass Clin. Microbiol. 2006; 44: PubMed Scopus (138) Google Scholar) and that bacteria of independently prepared groups can be accurately classified and identified by the unsupervised clustering and supervised E. J.L. G. X. A. Rapid identification of in clinical by matrix-assisted laser desorption of mass Clin. Microbiol. PubMed Scopus Google Scholar) We further to demonstrate the capability to identify bacteria in the of cells and in mixed bacterial isolates used in this were and by the of species were using the of American Society for Washington, D. C.2003Google Scholar). were on for 48 h followed by the presence of bacterial the were a The cells were from by and the intact was a target for further MALDI-TOF MS analysis independently prepared of bacterial isolates were 57 well bacterial isolates of the six most species of human pathogenic coli and were used for both unsupervised hierarchical clustering analysis used hierarchical clustering Genetic recognition analysis of and supervised analysis for construction of the classification The set well bacterial isolates of the bacterial species as the set and was used for of the constructed classification models set The set of bacterial including isolates than the six species used for the model was used for further evaluation of the classification models set that been on target was with of containing of acid in with the for MALDI-TOF MS was to acid or acid or the of for the was the MS spectra were we used the for this mass spectra in the were on an mass after the was A laser and the a of spectrum a of laser with a mass of by Mass was using a of peptides and proteins and to mass than reproducibility was by applying the bacterial isolates to different on the followed by MALDI-TOF MS analysis using the as the mass spectra of was used for peak to mass peak of and analysis corresponding peak the spectra set was The peak combined with was to of for unsupervised The data were to have a of and of and was using the correlation and we m/z values with than species and to further the we used the method to and their recognition by the method for as well as an of bacterial isolates set rapid we the and Genetic Algorithm in the for model In the model construction 57 clinical isolates of the were used to models as well as Identification was as to the m/z values in the The of the classification models was evaluated by recognition capability and is the of in a data set and is the of in a data and is the of in a data set and is the of in a data is to the of the classification is to of the classification set containing isolates was analyzed in a set to examine the of the isolates set from the clinical were used to the of the rapid classification The results were with those by the microbiologic The and were used to the and of the is the of in a data set and is the of and is the of from those species used for the model in a data set and is the of coli and were in for h before the cell were with to the of The of bacteria was by on after of was MALDI target for analysis. methods to bacterial proteins for protein profiling by MALDI-TOF including extraction of by and of using methods and Chen H.L. evaluation of the of procedures on proteome 2006; PubMed Scopus Google Scholar), were used but with low peak contents and low reproducibility of MS spectra not In directly subjecting the bacterial colonies without further extraction to MALDI-TOF MS analysis in rich peak contents of the spectra and the reproducibility not the approach was used to MS spectra for analysis in reproducibility was by bacterial isolates for MALDI-TOF MS analysis not the work of this 57 well bacterial isolates of the six most human pathogenic bacterial species were used to examine the feasibility of bacterial classification and identification based on the m/z spectra by MALDI-TOF were unsupervised hierarchical clustering with and direct model construction using the supervised methods as Genetic Algorithm. The and of the constructed models were evaluated by and using of independently prepared bacterial isolates set and set We used an to bacterial isolates on the of in their MS spectral the 57 identified six that to the six bacterial species We reduced the of m/z values for We m/z values that of bacteria via that were used for in the 57 isolates were classified into six groups corresponding to the six bacterial species. the of the m/z values isolates into six groups the of m/z values as was further and the were in the of MS was reduced to six via the method with on the of classification A and and was further using an set of bacterial isolates set The MS spectra of the 57 bacterial isolates of the six most species pathogenic to were used to the classification models and including the and were A of models were and including their and are in model and of recognition and of set for the classification of of of set in a the of bacterial classification and identification with the prepared set was to analysis model a containing 18 m/z values was for evaluation of its and in bacterial identification using the of isolates set including isolates of bacteria than the species used for the model in for of which was as K. the isolates were from the six bacterial and the isolates were a of and a of model for bacterial in a results of a for bacterial identification on set using model set by were identified using a by model was as a to the m/z values in model in the of in the of was as K. using model were identified using a of American Society for Washington, D. C.2003Google Identification was as a to the m/z values in model in the of in a was as K. using model We a of bacterial to examine the of bacterial cells for identification using the rapid protein profiling and model as the bacterial and E. were The for identification was to be for E. coli and for the results for E. the we the capability of bacteria from bacterial We mixed an of different species of colonies as E. coli and E. and K. E. K. and E. K. and and E. K. and B. of the bacterial species in the were identified in the mixtures containing of the six species was maintained as the of different species with to not for and human pathogenic microorganisms have high sensitivity and specificity, simple procedures, and on of the to the of and These have particularly after the of in the in as well as the of human as in and the of Rev. Microbiol. 2003; PubMed Scopus Google Scholar, K. MS on the Chem. 2006; PubMed Scopus Google Scholar). In this study, we systematically evaluated the feasibility of applying mass spectrometry techniques to we for the of protein for a rapid and accurate identification of bacteria using MS We different and that directly subjecting bacterial colonies without further protein extraction to MALDI-TOF MS analysis the m/z contents with high reproducibility. have been before (16Wang Z. Russon L. Li L. Roser D.C. Long S.R. Investigation of spectral reproducibility in direct analysis of bacteria proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Rapid Commun. Mass Spectrom. 1998; 12: 456-464Crossref PubMed Scopus (196) Google Scholar, 17Yao Z.P. Afonso C. Fenselau C. Rapid microorganism identification with on-slide proteolytic digestion followed by matrix-assisted laser desorption/ionization tandem mass spectrometry and database searching.Rapid Commun. Mass Spectrom. 2002; 16: 1953-1956Crossref PubMed Scopus (47) Google Scholar, M.A. Davey S.N. Edwards-Jones V. Gordon D.B. The rapid identification of intact microorganisms using mass spectrometry.Nat. Biotechnol. 1996; 14: 1584-1586Crossref PubMed Scopus (496) Google Scholar, Jr., J.O. Rapid identification of intact whole bacteria based on spectral using matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry.Rapid Commun. Mass Spectrom. 1996; 10: PubMed Scopus Google Scholar, S.L. Valentine N.B. A.J. Kingsley M.T. Wahl K.L. of an for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of bacteria.J. Mass Spectrom. 1999; 10: PubMed Scopus (48) Google Scholar, V. Claydon M.A. D.J. J. A.J. Gordon D.B. Rapid and by intact cell mass Microbiol. PubMed Scopus Google Scholar, J. A.J. Edwards-Jones V. Gordon D.B. cell mass spectrometry used to and Microbiol. Methods. 2002; 48: PubMed Scopus Google Scholar, D. J.O. the and reproducibility of MALDI mass spectra from whole bacteria Mass Spectrom. 2003; 14: PubMed Scopus Google Scholar, V. B. Rapid identification of bacterial species by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Rapid Commun. Mass Spectrom. 2004; PubMed Scopus Google Scholar, J.P. G. D.N. profiling of intact by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Anal. Chem. 2004; PubMed Scopus Google Scholar). we of to the that MALDI-TOF MS techniques can be an accurate method for bacterial classification and identification. We used an unsupervised method using hierarchical clustering analysis in with and for and a supervised method of direct model construction based on known bacterial species. of the the of bacterial classification and identification in independently prepared of bacterial isolates and application of MALDI-TOF MS for rapid bacterial identification has been before J.P. Snyder A.P. Classification and identification of bacteria using mass spectrometry-based proteomics.Expert Rev. Proteomics. 2005; 2: 863-878Crossref PubMed Scopus (56) Google Scholar, 23Bright J.J. Claydon M.A. Soufian M. Gordon D.B. Rapid typing of bacteria using matrix-assisted laser desorption ionisation time-of-flight mass spectrometry and pattern recognition software.J. Microbiol. Methods. 2002; 48: 127-138Crossref PubMed Scopus (127) Google Scholar, 24Keys C.J. Dare D.J. Sutton H. Wells G. Lunt M. McKenna T. McDowall M. Shah H.N. Compilation of a MALDI-TOF mass spectral database for the rapid screening and characterisation of bacteria implicated in human infectious diseases.Infect. Genet. Evol. 2004; 4: PubMed Scopus Google Scholar, of bacteria by matrix-assisted laser and electrospray mass Microbiol. Rev. PubMed Scopus Google Scholar, E. J.L. G. X. A. Rapid identification of in clinical by laser desorption ionisation time-of-flight mass spectrometry Clin. Microbiol. PubMed Scopus Google Scholar). A database of than MALDI-TOF MS spectra with bacterial strain from most bacterial species has been and used for a rapid screening and characterization of bacteria implicated in human using spectrum fingerprinting analysis. However, the of identification this database and C.J. Dare D.J. Sutton H. Wells G. Lunt M. McKenna T. McDowall M. Shah H.N. Compilation of a MALDI-TOF mass spectral database for the rapid screening and characterisation of bacteria implicated in human infectious diseases.Infect. Genet. Evol. 2004; 4: PubMed Scopus Google Scholar). The low results were to of species the database C.J. Dare D.J. Sutton H. Wells G. Lunt M. McKenna T. McDowall M. Shah H.N. Compilation of a MALDI-TOF mass spectral database for the rapid screening and characterisation of bacteria implicated in human infectious diseases.Infect. Genet. Evol. 2004; 4: PubMed Scopus Google Scholar). we the classification of bacteria six different species Moreover we that independently prepared bacteria can be classified and identified by the classification models of 18 or fewer m/z bacteria than those used for model construction were also by the classification These are because the the the from and the the are for clinical and epidemiologic uses (16Wang Z. Russon L. Li L. Roser D.C. Long S.R. Investigation of spectral reproducibility in direct analysis of bacteria proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Rapid Commun. Mass Spectrom. 1998; 12: 456-464Crossref PubMed Scopus (196) Google Scholar, D. J.O. the and reproducibility of MALDI mass spectra from whole bacteria Mass Spectrom. 2003; 14: PubMed Scopus Google Scholar). we the sensitivity of for bacterial identification. We applied a of a to for MS which we that was the of cells for bacterial identification in a In mixtures from different 104 was the of cells for identification. sensitivity can be further by MS database and analysis are important because a bacterial in than is regarded as the bacterial with clinical of this is than the of assays. that microorganisms from clinical than can be to MS analysis using and of microorganisms from without for further by we the capability of bacteria in mixtures containing species. on the application of MS techniques used colonies for bacterial identification by MS of the target microorganisms and procedures of bacterial isolation, selection, and culture procedures were Wahl K.L. Jarman K.H. Valentine N.B. Petersen C.E. Kingsley M.T. A.J. of microbial mixtures by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.Anal. Chem. 2002; PubMed Scopus Google Scholar) the of fingerprinting to identify a bacterial species in However, fingerprinting analysis was dependent on the of of the bacterial which not be by from because of the of MS analysis. In this study, we mixed different bacterial species for MALDI-TOF used the classification and that species be identified in mixed containing to six species. In to the the classification models containing m/z values not the of bacterial classification and reduced the from or but also the capability to identify different bacterial species in mixed even after using bacteria than those used for the model construction. the for microorganism identification directly from clinical without culture by MS techniques in the A. Mass spectrometry for species or strain identification after culture or without culture: past, present, and future.J. Clin. Microbiol. 2006; 44: 2677-2680Crossref PubMed Scopus (69) Google Scholar). of the proteins of model were identified as ribosomal as m/z ribosomal protein of ribosomal protein of and ribosomal protein of have been to ribosomal proteins as for bacterial identification to their high abundance and in cell L. K. H. M. H. T. Characterization of ribosomal proteins as biomarkers for matrix-assisted laser desorption/ionization mass spectral identification of Commun. Mass Spectrom. 2006; 20: PubMed Scopus Google Scholar, D.M. P.A. ribosomal protein to bacterial using matrix-assisted laser desorption/ionization mass spectrometry.Proteomics. 2005; 5: PubMed Scopus (47) Google Scholar). Further to examine ribosomal proteins can be as the for further the which have been identified by the methods in this study, are warranted. In we systematically the feasibility of applying MS techniques for rapid and accurate bacterial We that directly applying a bacterial to MALDI-TOF MS is a simple and reliable method for rapid protein The of a of m/z values of the whole spectra not the on spectrum but also a bacterial identification bacterial species in mixed can be identified with a than that regarded as for the that mass spectrometry techniques can be an alternative for a highly and accurate bacterial identification. is by further database and analysis a rapid and accurate identification of human pathogenic microorganisms without culture be in the near future. with