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K.-C. Wang drafted the manuscript and performed mutant strain construction and PDE assay. Y.-H. Hsu helped the experimental design and data analysis. Y.-N. Huang assisted molecular cloning and site-directed mutagenesis, protein purification experiments. K.-S. Yeh conceived and coordinated this study and also helped to draft the manuscript. All authors read and approved the final manuscript.”
“Background Pneumonia is the most common cause of death related to infectious diseases. Even after aggressive antimicrobial treatment pneumococcal pneumonia causes mortalities of up to 10% [1]. Children

and young adults are susceptible to lower respiratory tract infection typically caused by Staphylococcus aureus Haemophilus influenzae and Pseudomonas aeruginosa[2]. Moreover, P. aeruginosa colonization of the lung is frequently found in cystic fibrosis patients, which worsens the prognosis of this disease [3]. Pneumonia signifcantly increases the average duration of intensive care unit (ICU) stays and mortality [4]. The diagnosis of nosocomial pneumonia often requires invasive and time consuming methods (e.g. bronchoscopy) [5]. Therefore, it is of utmost interest to develop a non-invasive method CYTH4 for the early diagnosis of this disease, preferably allowing the identification of the specific pathogens. Attempts on screening of volatile bacterial metabolites for detection and classification of virulent bacteria was already undertaken in the past. However, the vast majority of studies on volatile organic compounds (VOCs) released from bacteria included qualitative analyses only [6–10]. Also direct mass spectrometric methods were used for the investigation of VOC release, comprising selected ion flow tube mass spectrometry (SIFT-MS) [11, 12] and proton transfer reaction mass spectrometry (Selleckchem Idasanutlin PTR-MS) [13–15].