Analysis of VOCs Released of Pathogenic Bacteria of Ventilator Associated Pneumonia by Non-targeted Mass Spectrometry

Ventilator associated pneumonia (VAP) is an infectious disease in clinic with high incidence rate (about 5%-40%) and mortality (about 10%), which is mainly caused by bacteria. At present, the clinical diagnosis of VAP depends on the microbial pathogen diagnosis of sputum samples from the lower respiratory tract. The whole process takes more than 24 hours, which is easy to cause antibiotic misuse and initial treatment failure. In recent years, breath test has received widespread attention due to its non-invasive and convenient characteristics, which attempt to screen and diagnose VAP through analysis of volatile organic compounds (VOCs) in exhalation. Therefore, the research on characterization of VOCs released by VAP pathogens has certain guiding significance for the related breath tests. In this study, the main VAP pathogenic bacteria, including P. aeruginosa, S. aureus, E. coli, E. cloacae, K. pneumoniae, A. baumannii, S. maltophilia, and S. epidermidis, were cultured in tryptic soy broth (TSB) culture medium in vitro, and their headspace samples were obtained after 10 hours of shaking culture. Then, non-targeted detection of VOCs in the headspace was performed by using solid phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GC-MS). It was found that a total of 44 differential amounts of VOCs were released by the 8 strains. Subsequently, these bacterial VOCs were classified and discussed according to ketones, aldehydes, ethers, alcohols, acids, esters, alkanes, benzenes, amides, and (nitrogen-containing) heterocycles. These results showed that there was some consistency in the types of VOCs released by the 8 VAP pathogens, such as the production of dimethyl ether and methyl mercaptan. However, there were some differences in the released VOCs among the different pathogens. For example, only S. aureus released 2-butanone and 3-hydroxy-2-butanone, only E. coli produced acetic acid, only E. coli, S. maltophilia, and S. aureus produced N-nenenebc methylformamide. In addition, K. pneumoniae and P. aeruginosa released dimethyl disulfide (DMDS), and S. maltophilia released dimethyl trisulfide (DMTS). This study systematically reports the similarities and differences in the types of VOCs released by VAP pathogens, providing a reference and foundament for VAP related breath research. In the future, it is expected to achieve rapid and non-invasive screening of VAP through exhalation. However, this study did not detect clinically isolated strains or samples, and it was not possible to verify whether there were any differences in results between standard strains and clinical strains. In future work, it is necessary to consider the characteristic spectra of clinically isolated strains and the landmark VOCs in the exhalation of clinical patients.