Volatile organic compound profiles of pneumonia pathogens using thermal desorption gas chromatography with parallel mass and ion mobility spectrometry detection: A feasibility study

Hospital-acquired and ventilator-associated pneumonia are life-threatening infections in intensive care, yet rapid identification of causative pathogens remains a diagnostic challenge. Volatile organic compounds (VOCs) released by bacteria may support alternative diagnostic strategies, provided that reliable species-associated profiles can be established. This feasibility study applies a combined thermal desorption-gas chromatography-mass spectrometry-ion mobility spectrometry (TD-GC-MS-IMS) platform to characterize time-resolved VOC profiles of clinically relevant pneumonia pathogens. Clinical isolates of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, and Streptococcus pneumoniae were cultivated, and headspace samples were collected over 24 h using a custom-built sampling setup designed for controlled and reproducible VOC collection. The dual-detector setup enabled direct assignment of retention time, drift time, and mass spectra, facilitating reliable compound identification and confirmation with authentic standards. Distinct species-associated VOCs were identified. These included indole for Escherichia coli, acetoin and branched-chain aldehydes for Staphylococcus aureus, methyl thiocyanate and dimethyl disulfide for Pseudomonas aeruginosa, and dimethyl disulfide together with an IMS-specific unknown compound for Acinetobacter baumannii. Importantly, these markers remained detectable in defined mixed cultures, underscoring their robustness under more complex conditions. Our findings highlight both the potential and the current limitations of VOC-based diagnostics, providing a validated reference framework that can support the development of GC-IMS databases and future translational studies in clinical respiratory specimens.