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1.
Microbial volatiles as diagnostic biomarkers of bacterial lung infection in mechanically ventilated patients
Waqar M Ahmed, Dominic Fenn, Iain R. White, Breanna Dixon, Tamara M E Nijsen, Hugo H Knobel, Paul Brinkman, Pouline M P van Oort, Marcus J Schultz, Paul Dark, Royston Goodacre, Timothy Felton, Lieuwe D J Bos, Stephen J. Fowler, 2022, izvirni znanstveni članek

Opis: Background Early and accurate recognition of respiratory pathogens is crucial to prevent increased risk of mortality in critically ill patients. Microbial-derived volatile organic compounds (mVOCs) in exhaled breath could be used as non-invasive biomarkers of infection to support clinical diagnosis. Methods In this study, we investigated the diagnostic potential of in vitro confirmed mVOCs in the exhaled breath of patients under mechanically ventilation from the BreathDx study. Samples were analysed by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). Results Pathogens from bronchoalveolar lavage (BAL) cultures were identified in 45/89 patients and S. aureus was the most commonly identified pathogen (n = 15). Out of 19 mVOCs detected in the in vitro culture headspace of four common respiratory pathogens (Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli), 14 were found in exhaled breath samples. Higher concentrations of two mVOCs were found in the exhaled breath of patients infected with S. aureus compared to those without (3-methylbutanal p < 0.01. AUROC = 0.81-0.87 and 3-methylbutanoic acid p = 0.01. AUROC = 0.79-0.80). In addition, bacteria identified from BAL cultures which are known to metabolise tryptophan (Escherichia coli, Klebsiella oxytoca and Haemophilus influenzae) were grouped and found to produce higher concentrations of indole compared to breath samples with culture-negative (p = 0.034) and other pathogen-positive (p = 0.049) samples. Conclusions This study demonstrates the capability of using mVOCs to detect the presence of specific pathogen groups with potential to support clinical diagnosis. Although not all mVOCs were found in patient samples within this small pilot study, further targeted and qualitative investigation is warranted using multi-centre clinical studies.
Ključne besede: Breath, VOCs, infection, respiratory pathogens, VAP
Objavljeno v RUNG: 28.11.2022; Ogledov: 1356; Prenosov: 0
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2.
Composition and diversity analysis of the lung microbiome in patients with suspected ventilator-associated pneumonia
Dominic Fenn, Mahmoud Abdel-Aziz, Pouline van Oort, Paul Brinkman, Waqar Ahmed, Timothy Felton, Antonio Artigas, Pedro Póvoa, Ignacio Martin-Loeches, Marcus Schultz, Paul Dark, Stephen Fowler, Iain R. White, 2022, izvirni znanstveni članek

Opis: Background: Ventilator-associated pneumonia (VAP) is associated with high morbidity and health care costs, yet diagnosis remains a challenge. Analysis of airway microbiota by amplicon sequencing provides a possible solution, as pneumonia is characterised by a disruption of the microbiome. However, studies evaluating the diagnostic capabilities of microbiome analysis are limited, with a lack of alignment on possible biomarkers. Using bronchoalveolar lavage fluid (BALF) from ventilated adult patients suspected of VAP, we aimed to explore how key characteristics of the microbiome differ between patients with positive and negative BALF cultures and whether any differences could have a clinically relevant role. Methods: BALF from patients suspected of VAP was analysed using 16s rRNA sequencing in order to: (1) differentiate between patients with and without a positive culture; (2) determine if there was any association between microbiome diversity and local inflammatory response; and (3) correctly identify pathogens detected by conventional culture. Results: Thirty-seven of 90 ICU patients with suspected VAP had positive cultures. Patients with a positive culture had significant microbiome dysbiosis with reduced alpha diversity. However, gross compositional variance was not strongly associated with culture positivity (AUROCC range 0.66–0.71). Patients with a positive culture had a significantly higher relative abundance of pathogenic bacteria compared to those without [0.45 (IQR 0.10–0.84), 0.02 (IQR 0.004–0.09), respectively], and an increased interleukin (IL)-1β was associated with reduced species evenness (rs = − 0.33, p < 0.01) and increased pathogenic bacteria presence (rs = 0.28, p = 0.013). Untargeted 16s rRNA pathogen detection was limited by false positives, while the use of pathogen-specific relative abundance thresholds showed better diagnostic accuracy (AUROCC range 0.89–0.998). Conclusion: Patients with positive BALF culture had increased dysbiosis and genus dominance. An increased caspase-1-dependent IL-1b expression was associated with a reduced species evenness and increased pathogenic bacterial presence, providing a possible causal link between microbiome dysbiosis and lung injury development in VAP. However, measures of diversity were an unreliable predictor of culture positivity and 16s sequencing used agnostically could not usefully identify pathogens; this could be overcome if pathogen-specific relative abundance thresholds are used.
Ključne besede: Microbiome, Next-generation sequencing, Ventilator-associated pneumonia
Objavljeno v RUNG: 26.10.2022; Ogledov: 1122; Prenosov: 0
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3.
Untargeted molecular analysis of exhaled breath as a diagnostic test for ventilator-associated lower respiratory tract infections (BreathDx)
Pouline M. van Oort, Tamara M. E. Nijsen, Iain R. White, Hugo Knobel, Timothy Felton, Nicholas J. W. Rattray, Oluwasola Lawal, Murtaza Bulut, Waqar Ahmed, Antonio Artigas, 2021, drugi znanstveni članki

Opis: Patients suspected of ventilator-associated lower respiratory tract infections (VA-LRTIs) commonly receive broad-spectrum antimicrobial therapy unnecessarily. We tested whether exhaled breath analysis can discriminate between patients suspected of VA-LRTI with confirmed infection, from patients with negative cultures. Breath from 108 patients suspected of VA-LRTI was analysed by gas chromatography-mass spectrometry. The breath test had a sensitivity of 98% at a specificity of 49%, confirmed with a second analytical method. The breath test had a negative predictive value of 96% and excluded pneumonia in half of the patients with negative cultures. Trial registration number: UKCRN ID number 19086, registered May 2015.
Ključne besede: ventilator-associated pneumonia, breath analysis, volatile organic compounds, metabolomics, intensive care, hospital acquired infections
Objavljeno v RUNG: 07.09.2021; Ogledov: 4269; Prenosov: 0
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4.
Detection of particle-phase polycyclic aromatic hydrocarbons in Mexico City using an aerosol mass spectrometer
Katja Džepina, Janet Arey, Linsey C. Marr, D. Worsnop, Dara Salcedo, Q. Zhang, Timothy B. Onasch, Luisa T. Molina, Mario J. Molina, Jose L. Jimenez, 2007, izvirni znanstveni članek

Opis: We report the quantification of ambient particle-bound polycyclic aromatic hydrocarbons (PAHs) for the first time using a real-time aerosol mass spectrometer. These measurements were carried out during the Mexico City Metropolitan Area field study (MCMA-2003) that took place from March 29 to May 4, 2003. This was the first time that two different fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. This paper focuses on the technical aspects of PAH detection in ambient air with the Aerodyne AMS equipped with a quadrupole mass analyzer (Q-AMS), on the comparison of PAHs measured by the Q-AMS to those measured with the other two techniques, and on some features of the ambient results. PAHs are very resistant to fragmentation after ionization. Based on laboratory experiments with eight PAH standards, we show that their molecular ions, which for most particulate PAHs in ambient particles are larger than 200 amu, are often the largest peak in their Q-AMS spectra. Q-AMS spectra of PAH are similar to those in the NIST database, albeit with more fragmentation. We have developed a subtraction method that allows the removal of the contribution from non-PAH organics to the ion signals of the PAHs in ambient data. We report the mass concentrations of all individual groups of PAHs with molecular weights of 202, 216, 226 + 228, 240 + 242, 250 + 252, 264 + 266, 276 + 278, 288 + 290, 300 + 302, 316 and 326 + 328, as well as their sum as the total PAH mass concentration. The time series of the Photoelectric Aerosol Sensor (PAS) and Q-AMS PAH measurements during MCMA-2003 are well correlated, with the smallest difference between measured PAH concentrations observed in the mornings when ambient aerosols loadings are dominated by fresh traffic emissions. The Q-AMS PAH measurements are also compared to those from GC–MS analysis of filter samples. Several groups of PAHs show agreement within the uncertainties, while the Q-AMS measurements are larger than the GC–MS ones for several others. In the ambient Q-AMS measurements the presence of ions tentatively attributed to cyclopenta[cd]pyrene and dicyclopentapyrenes causes signals at m/z 226 and 250, which are significantly stronger than the signals in GC–MS analysis of filter samples. This suggests that very labile, but likely toxic, PAHs were present in the MCMA atmosphere that decayed rapidly due to reaction during filter sampling, and this may explain at least some of the differences between the Q-AMS and GC–MS measurements.
Ključne besede: AMS, PAH, Mexico City
Objavljeno v RUNG: 11.04.2021; Ogledov: 3012; Prenosov: 0
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5.
Detection and quantification of exhaled volatile organic compounds in mechanically ventilated patients–comparison of two sampling methods
Iain R. White, Pouline M. van Oort, Waqar Ahmed, Craig Johnson, Jonathan Bannard-Smith, Timothy Felton, Lieuwe D. Bos, Royston Goodacre, Paul Dark, Stephen J. Fowler, 2020, izvirni znanstveni članek

Opis: Exhaled breath analysis is a promising new diagnostic tool, but currently no standardised method for sampling is available in mechanically ventilated patients. We compared two breath sampling methods, first using an artificial ventilator circuit, then in “real life” in mechanically ventilated patients on the intensive care unit. In the laboratory circuit, a 24-component synthetic-breath volatile organic compound (VOC) mixture was injected into the system as air was sampled: (A) through a port on the exhalation limb of the circuit and (B) through a closed endo-bronchial suction catheter. Sorbent tubes were used to collect samples for analysis by thermal desorption-gas chromatography-mass spectrometry. Realistic mechanical ventilation rates and breath pressure–volume loops were established and method detection limits (MDLs) were calculated for all VOCs. Higher yields of VOCs were retrieved using the closed suction catheter; however, for several VOCs MDLs were compromised due to the background signal associated with plastic and rubber components in the catheters. Different brands of suction catheter were compared. Exhaled VOC data from 40 patient samples collected at two sites were then used to calculate the proportion of data analysed above the MDL. The relative performance of the two methods differed depending on the VOC under study and both methods showed sensitivity towards different exhaled VOCs. Furthermore, method performance differed depending on recruitment site, as the centres were equipped with different brands of respiratory equipment, an important consideration for the design of multicentre studies investigating exhaled VOCs in mechanically ventilated patients.
Ključne besede: Volatile organic compounds, infection, breath, ventilator associated pneumonia
Objavljeno v RUNG: 10.12.2020; Ogledov: 2578; Prenosov: 0
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6.
TD/GC–MS analysis of volatile markers emitted from mono- and co-cultures of Enterobacter cloacae and Pseudomonas aeruginosa in artificial sputum
Iain R. White, Oluwasola Lawal, Hugo Knobel, Weda Hans, Tamara M E Nijsen, Royston Goodacre, Stephen J. Fowler, Waqar M Ahmed, Antonio Artigas, Jonathan Barnard-Smith, Lieuwe D Bos, Marta Camprubi, Luis Coelho, Paul Dark, Alan Davie, Emili Diaz, Gemma Goma, Timothy Felton, Jan H Leopold, Pouline M P van Oort, Pedro Póvoa, Craig Portsmouth, 2018, izvirni znanstveni članek

Opis: Introduction: Infections such as ventilator-associated pneumonia (VAP) can be caused by one or more pathogens. Current methods for identifying these pathogenic microbes often require invasive sampling, and can be time consuming, due to the requirement for prolonged cultural enrichment along with selective and differential plating steps. This results in delays in diagnosis which in such critically ill patients can have potentially life-threatening consequences. Therefore, a non-invasive and timely diagnostic method is required. Detection of microbial volatile organic compounds (VOCs) in exhaled breath is proposed as an alternative method for identifying these pathogens and may distinguish between mono- and poly-microbial infections. Objectives: To investigate volatile metabolites that discriminate between bacterial mono- and co-cultures. Methods: VAP-associated pathogens Enterobacter cloacae and Pseudomonas aeruginosa were cultured individually and together in artificial sputum medium for 24 h and their headspace was analysed for potential discriminatory VOCs by thermal desorption gas chromatography–mass spectrometry. Results: Of the 70 VOCs putatively identified, 23 were found to significantly increase during bacterial culture (i.e. likely to be released during metabolism) and 13 decreased (i.e. likely consumed during metabolism). The other VOCs showed no transformation (similar concentrations observed as in the medium). Bacteria-specific VOCs including 2-methyl-1-propanol, 2-phenylethanol, and 3-methyl-1-butanol were observed in the headspace of axenic cultures of E. cloacae, and methyl 2-ethylhexanoate in the headspace of P. aeruginosa cultures which is novel to this investigation. Previously reported VOCs 1-undecene and pyrrole were also detected. The metabolites 2-methylbutyl acetate and methyl 2-methylbutyrate, which are reported to exhibit antimicrobial activity, were elevated in co-culture only. Conclusion: The observed VOCs were able to differentiate axenic and co-cultures. Validation of these markers in exhaled breath specimens could prove useful for timely pathogen identification and infection type diagnosis.
Ključne besede: Bacteria, Enterobacter cloacae, Gas Chromatography-Mass Spectrometry, Infection, Pseudomonas aeruginosa, Volatile organic compounds
Objavljeno v RUNG: 18.07.2019; Ogledov: 4570; Prenosov: 114
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