A HIGHLY DISCRIMINATORY METHOD FOR THE DIRECT COMPARISON OF 2 CLOSELY-RELATED BACTERIAL-POPULATIONS BY PYROLYSIS MASS-SPECTROMETRY

The ability of pyrolysis mass spectrometry (Py-MS) to discriminate bet ween paired groups of closely related bacteria has been examined. The technique was challenged with increasing levels of biological differen ce; from that between different subcultures of the same isolate of Sta phylococcus aureus, through that between separate isolates of the same strain and eventually to that between different staphylococcal specie s and Streptococcus pyogenes. By using an analytical method in which t he spectral data from any two groups can be directly compared at a tim e, it was shown that PB-MS was capable of measuring statistically sign ificant differences between staphylococci and Streptococcus pyogenes, between different Staphylococcus species and between two isolates of t he same strain of S. aureus from different sources. Two subcultures of the same isolate were found to be indistinguishable. The differing ma gnitude of the Py-MS-derived differences corresponded to the ''biologi cal differences'', being much larger between staphylococci and strepto cocci than between staphylococcal species and only just statistically significant between isolates of the same strain from different sources . The technique described allows the assessment of the magnitude and s ignificance of PyMS-derived differences between any two bacterial popu lations.