Tenax is not suitable

to adsorb as low molecular hydrocarbons as C3 and gives very poor adsorption efficiency for C4 [36]. Therefore multibed sorption tubes were applied in the present work within which carbon molecular sieves (Carboxen 569 and Carboxen 1000) very efficiently trap the most volatile analytes (propane, butane). Consequently, the analyses of these compounds were performed at the trace level, giving the limit of detection (LOD) for propane at 33pptv and for butane 24pptv (data not shown). Diverse hydrocarbons were detected mostly in low amount in the headspace of S. aureus and P. aeruginosa cultures comprising 6 and 9 different compounds, respectively. Concerning S. aureus solely 2-methylpropene (GS-9973 datasheet Figure 1e) and (E)-2-butene reached moderately high concentration levels. Intriguingly, all hydrocarbons released by S. aureus consist of 4 carbon atoms (except propane) while P. aeruginosa released larger alkenes mostly GF120918 in the range of C9 – C12. Amongst all volatile metabolites released from P. aeruginosa hydrocarbons were one of the most important chemical classes. In particular, 1-undecene and isoprene were significantly released already at the first sampling

time-point, reaching as high concentration as ~300ppbv after 24 h of bacteria growth. Importantly concentrations of 1-undecene in headspace samples were very well correlated with the proliferation rate of P. aeruginosa (Figure 1f). Isoprene, the second most abundant check details hydrocarbon secreted by P. aeruginosa whose biosynthesis via methylerythritol phosphate (MEP) pathway was found in a wide range of plants and microorganisms [37, 38] reached the maximum concentration of 24

ppbv after 24 h of bacteria growth. All remaining hydrocarbons were detected at low (e.g. 1-dodecene) or even extremely low concentration (e.g. 2-methyl-2-butene, 1-decene in Table 3A). Volatile nitrogen-containing compounds (VNCs) A smaller, Chloroambucil but very interesting class of compounds exclusively released by P. aeruginosa comprised volatile nitrogen containing compounds (VNCs). The preeminent example is pyrrole, which was detected already after 1.5 h and reached the maximum concentration of ~50ppbv after 3 h of bacteria growth. Interestingly, apart from 3-methylpyrrole, the VNCs had an unconventional pattern of release, reaching the maximum concentration at early time-points and continuously decreasing in the course of experiment, while they were absent in the medium control. Discussion The aim of this work was to investigate whether the detection and perhaps identification of bacteria can be achieved by the determination of characteristic volatile metabolites released. This work should provide the basis for the application of breath-gas analysis in the early and non-invasive diagnosis of bacterial lung infections by monitoring the presence of the specific pathogen-derived markers in exhaled breath.