Molecular analysis of volatile metabolites released specifically by staphylococcus aureus and pseudomonas aeruginosa

Abstract

The routinely used microbiological diagnosis of ventilator associated pneumonia (VAP) is timeconsuming and often requires invasive methods for collection of human specimens (e.g. bronchoscopy). Therefore,it is of utmost interest to develop a non-invasive method for the early detection of bacterial infection in ventilatedpatients, preferably allowing the identification of the specific pathogens. The present work is an attempt to identifypathogen-derived volatile biomarkers in breath that can be used for early and non- invasive diagnosis of ventilatorassociated pneumonia (VAP). For this purpose, in vitro experiments with bacteria most frequently found in VAPpatients, i.e. Staphylococcus aureus and Pseudomonas aeruginosa, were performed to investigate the release orconsumption of volatile organic compounds (VOCs).Results: Headspace samples were collected and preconcentrated on multibed sorption tubes at different timepoints and subsequently analyzed with gas chromatography mass spectrometry (GC-MS). As many as 32 and 37volatile metabolites were released by S. aureus and P. aeruginosa, respectively. Distinct differences in thebacteria-specific VOC profiles were found, especially with regard to aldehydes (e.g. acetaldehyde, 3-methylbutanal),which were taken up only by P. aeruginosa but released by S. aureus. Differences in concentration profiles were alsofound for acids (e.g. isovaleric acid), ketones (e.g. acetoin, 2-nonanone), hydrocarbons (e.g. 2-butene,1,10-undecadiene), alcohols (e.g. 2-methyl-1-propanol, 2-butanol), esters (e.g. ethyl formate, methyl 2-methylbutyrate),volatile sulfur compounds (VSCs, e.g. dimethylsulfide) and volatile nitrogen compounds (VNCs, e.g. 3-methylpyrrole).Importantly, a significant VOC release was found already 1.5 hours after culture start, corresponding to cell numbersof ∼8106 [CFUs/ml].Conclusions: The results obtained provide strong evidence that the detection and perhaps even identification ofbacteria could be achieved by determination of characteristic volatile metabolites, supporting the clinical use ofbreath-gas analysis as non-invasive method for early detection of bacterial lung infections. © 2012 Filipiak et al.; licensee BioMed Central Ltd.