MICROORGANISM GRAM-TYPE DIFFERENTIATION BASED ON PYROLYSIS MASS-SPECTROMETRY OF BACTERIAL FATTY-ACID METHYL-ESTER EXTRACTS

Curie-point pyrolysis (Py)-mass spectrometry has been used to differen tiate 19 microorganisms by Gram type on the basis of the methyl esters of their fatty acid distribution. The mass spectra of gram-negative m icroorganisms were characterized by the presence of palmitoleic acid ( C-16:1) and oleic acid (C-18:1), as well as a higher abundance of palm itic acid (C-16:0) than pentadecanoic acid (C-15:0). For gram-positive microorganisms, a signal of branched C-15:0 (isoC(15:0) and/or anteis oC(15:0)) more intense than that of palmitic acid was observed in the mass spectra. Principal components analysis of these mass spectral dat a segregated the microorganisms investigated in this study into three discrete clusters that correlated to their gram reactions and pathogen icities. Further tandem mass spectrometric analysis demonstrated that the nature of the C-15:0 fatty acid isomer (branched or normal) presen t in the mass spectrum of each microorganism was important for achievi ng the classification into three clusters.