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

Abstract

BackgroundThe routinely used microbiological diagnosis of ventilator associated pneumonia (VAP) is time consuming 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 ventilated patients, preferably allowing the identification of the specific pathogens. The present work is an attempt to identify pathogen-derived volatile biomarkers in breath that can be used for early and non- invasive diagnosis of ventilator associated pneumonia (VAP). For this purpose, in vitro experiments with bacteria most frequently found in VAP patients, i.e. Staphylococcus aureus and Pseudomonas aeruginosa, were performed to investigate the release or consumption of volatile organic compounds (VOCs).ResultsHeadspace samples were collected and preconcentrated on multibed sorption tubes at different time points and subsequently analyzed with gas chromatography mass spectrometry (GC-MS). As many as 32 and 37 volatile metabolites were released by S. aureus and P. aeruginosa, respectively. Distinct differences in the bacteria-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 also found 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 numbers of ~8*106 [CFUs/ml].ConclusionsThe results obtained provide strong evidence that the detection and perhaps even identification of bacteria could be achieved by determination of characteristic volatile metabolites, supporting the clinical use of breath-gas analysis as non-invasive method for early detection of bacterial lung infections.

A rapid method for breath analysis in cystic fibrosis patients

“…aeruginosa [17,18] and S. aureus [19] in vitro revealing numerous compounds in the headspace of these microorganisms. Recently, 2-aminoacetophenone was getting into the focus as biomarker molecule for P.…”

Exhaled breath metabolomics as a noninvasive diagnostic tool for acute respiratory distress syndrome

“…Exhaled VOCs can be of systemic origin, can be produced in the lung (e.g. under influence of oxidative stress and inflammatory response) or can be the result of bacterial metabolism [16][17][18][19][20][21]. Pre-clinical studies provide evidence that lung injury induces changes in exhaled metabolites [17,22].…”

Detection of exogenous VOCs as a novel in vitro diagnostic technique for the detection of pathogenic bacteria

“…Recently several mass spectrometric An increase in a signal with m/z of 70 was associated with growth of P. aeruginosa. Candida species showed increased production of an m/z signal of 140 whereas a m/z signal of 101 was only observed in cultures of S. aureus, among the bacteria tested, and was tentatively attributed to the production of isovaleric acid which has been reported previously as a biomarker for S. aureus [46]. E. coli cultures also produced a m/z signal of 116 attributed to the deprotonated form of indole, with E. coli being a well-known indole producing species [6].…”

“…aureus, and Neisseria meningitidis were determined in fastidious antimicrobial neutralization BacT/ALERT® bottles, the effect of antibiotics on VOC production was determined for E. coli with Gentamicin and S. aureus with Flucloxacillin using standard aerobic bottles [46]. Blood samples taken from healthy individuals were added to the BacT/ALERT® bottles, and inoculated with 10 CFU of test species to simulate a bacteraemia (10 3 CFU for susceptibility experiments) with incubation at 37 o C. As opposed to the previously described study in which all ions over a specified mass range were observed for headspace analyses, in this study a number of VOCs were identified as suitable biomarkers for the test species including: 2-aminoacetophenone, ammonia, dimethyldisulfide (DMDS), dimethylsulfide (DMS), formaldehyde, ethanol, hydrogen sulfide, indole, methanethiol, pentanols, and propanol [47].…”