Novel biomarkers for Gram-type differentiation of bacteria by pyrolysis-gas chromatography-mass spectrometry

The pyrolysis-gas chromatography (Py-GC) module of a fielded, briefcase Py-GC-ion mobility spectrometry (Py-GC-IMS) biodetector is shown to generate a set of specific products that reflect the biochemical composition of bacterial cell envelopes. A prominent pyrolysis biomarker derived from the cell walls of Gram-positive bacteria has been identified as pyridine-2-carboxamide (2-picolinamide). Experiments performed using model polymers strongly suggest its origin from the thermal rearrangements of the meso-diaminopimelic acid and/or l-lysine peptide residue cross-linker species in peptidoglycan. Biomarkers produced by pyrolysis from Gram-negative organisms were found to originate from the lipid A portion of the lipopolysaccharide (LPS) cell surface. These biomarkers include pyrolysis products of the 3-hydroxymyristate fatty acid residues such as 1-tridecene, dodecanal and methylundecylketone. A nitrile derivative from amide bound fatty acids and free fatty acids originally present as ester bound moieties in lipid A are also observed upon bacterial pyrolysis. The presence of these biomarkers directly reflect similar information content provided by a classical Gram staining procedure and make them suitable for direct Gram-type differentiation of micro-organisms.