Alice Alcock

University Hospital Of North Staffordshire NHS Trust, Stoke-upon-Trent, England, United Kingdom

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Publications (7)23.27 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: Following our recent in vitro study of the volatile compounds emitted into the gas phase by the respiratory pathogens Pseudomonas aeruginosa (PA), and most recently Staphylococcus aureus (SA), Streptococcus pneumoniae (SP) and Haemophilus influenzae (HI), we have extended this work to the investigation of the volatile compounds emitted by in vitro cultures of the common respiratory fungus Aspergillus fumigatus (AF). The measurements were achieved using selected ion flow tube mass spectrometry (SIFT-MS) by which real time analyses of trace volatile compounds can be achieved without disturbing the cultures. It is seen that copious amounts of ammonia and the organosulphur compounds methanethiol, dimethyl sulphide and dimethyl disulphide are produced by AF cultures. These may be sufficient to allow for non-invasive detection of the AF in the airways of infected patients by breath analysis. AF also efficiently absorbs and metabolises the aldehydes acetaldehyde, butanal and pentanal from the supportive medium (brain-heart infusion broth). Preliminary studies of the volatile compounds emitted by co-cultures of AF with PA, SA and SP revealed that the biomarker HCN (for PA) is not compromised by the presence of AF, and the organosulphur compounds (for AF) are not compromised by the presence of SA or SP.
    No preview · Article · Aug 2014 · Analytical methods
  • [Show abstract] [Hide abstract] ABSTRACT: In the light of the exciting recent developments in the detection of Pseudomonas aeruginosa in the breath of cystic fibrosis patients by measuring exhaled HCN, an in vitro study has been conducted to identify and quantify the volatile compounds emitted into the gas phase by other respiratory pathogens. Selected ion flow tube mass spectrometry (SIFT-MS) was used to investigate clinical isolates of Staphylococcus aureus (SA), Streptococcus pneumoniae (SP), and Haemophilus influenzae (HI). Six volatile compounds, mainly alcohols, ketones and aldehydes, were found to be elevated in the headspace of SA cultures and eight were elevated in the SP cultures. It is clear from the mass spectra that a number of other compounds were present at low levels that, as yet, cannot be identified by SIFT-MS alone. Only indole and ethanol were somewhat elevated in the headspace of some of the HI cultures. Principal component analyses (PCA) indicated that the SA cultures clearly separated into two distinct groups in terms of their volatile compound emissions. This may relate to genetic or phenotypic differences. It is postulated that the very efficient production of ethanol and acetaldehyde by SA and SP may provide indicators of airways infection by these bacteria if the levels of these compounds are elevated in exhaled breath above those levels expected due to their normal endogenously produced levels. Plans are in place to check this postulate by breath analysis studies involving patients with pulmonary infections with these organisms.
    No preview · Article · Apr 2014 · Analytical methods
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    [Show abstract] [Hide abstract] ABSTRACT: Biofilm cultures of Burkholderia cepacia complex (BCC) infection have been found to generate the nonvolatile cyanide ion. We investigated if gaseous hydrogen cyanide (HCN) was a marker of BCC infection. Selected ion flow tube mass spectrometry analysis showed HCN was not elevated in the headspace of planktonic or biofilm cultures or in the exhaled breath of adult cystic fibrosis patients with chronic BCC infection. HCN is therefore not an in vitro or in vivo marker of BCC. Copyright © 2013, American Society for Microbiology. All Rights Reserved.
    Full-text · Article · Aug 2013 · Journal of clinical microbiology
  • [Show abstract] [Hide abstract] ABSTRACT: Hydrogen cyanide (HCN) and 2-aminoacetophenone (2-AA; H2NC6H4COCH3) are possible biomarkers of pulmonary Pseudomonas aeruginosa (PA) infection that could be used in an exhaled breath test. All factors affecting their production need to be investigated, including the culture conditions: planktonic (free-floating) or biofilm (non-motile communities attached to a solid surface). In vivo, the change from planktonic to biofilm growth is signalled when a certain population density is reached. Using selected ion flow tube mass spectrometry, SIFT-MS, we have analysed HCN and 2-AA produced by 12 genotyped PA samples, cultured under both planktonic and biofilm conditions after 24, 48, 72 and 96 hours of incubation. The 12 samples included 3 different strains (genotypes), 50% of which had a mucoid phenotype and 50% had a non-mucoid phenotype. All samples produced significant concentrations of HCN; median (25th to 75th percentiles, IQR) concentration: 144 (61–512) parts-per-billion by volume (ppbv). Multivariate analysis showed HCN production varied dependent on genotype (p = 0.0014), culture duration (p = 0.005) and phenotype (p < 0.001) but not culture conditions (planktonic/biofilm). Much smaller concentrations of 2-AA were detected, median (IQR) concentration 1.8 (1.3–3) ppbv, despite which, multivariate analysis showed production was affected by genotype (p < 0.001) and culture duration (p = 0.007) but not phenotype or culture conditions. These data show that biofilm formation does not affect HCN production by PA and supports its use as a biomarker of PA infection. The concentrations of 2-AA are much lower than previous studies have shown. The reason for this is unclear but it raises questions about its suitability as a biomarker of PA infection.
    No preview · Article · Oct 2012 · Analytical methods
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    Full-text · Article · Jun 2011 · Journal of Cystic Fibrosis
  • [Show abstract] [Hide abstract] ABSTRACT: There is increasing interest in using the cyanogenic properties of Pseudomonas aeruginosa to develop a nonmicrobiological method for its detection. Prior to this, the variation in cyanide production between different P. aeruginosa strains needs to be investigated. Hydrogen cyanide (HCN) released into the gas phase by 96 genotyped P. aeruginosa samples was measured using selected ion flow tube-mass spectrometry after 24, 48, 72 and 96 h of incubation. The HCN produced by a range of non-P. aeruginosa cultures and incubated blank plates was also measured. All P. aeruginosa strains produced more HCN than the control samples, which generated extremely low levels. Analysis across all time-points demonstrated that nonmucoid samples produced more HCN than the mucoid samples (p=0.003), but this relationship varied according to strain. There were clear differences in the headspace HCN concentration for different strains. Multivariate analysis of headspace HCN for the commonest strains (Liverpool, Midlands_1 and Stoke-on-Trent, UK) revealed a significant effect of strain (p<0.001) and a borderline interaction of strain and phenotype (p=0.051). This evidence confirms that all P. aeruginosa strains produce HCN but to varying degrees and generates interest in the possible future clinical applications of the cyanogenic properties of P. aeruginosa.
    No preview · Article · Apr 2011 · European Respiratory Journal
  • [Show abstract] [Hide abstract] ABSTRACT: Pseudomonas aeruginosa (PA) is associated with a distinctive smell produced by a combination of volatile compounds (VCs). Selected ion flow tube mass spectrometry (SIFT-MS) provides a novel and rapid methodology for rapid, accurate detection of trace quantities (parts per billion; ppb) of VCs in air. We studied the VCs produced by different isolates of PA cultures in vitro from patients with cystic fibrosis. Twenty-one patients with cystic fibrosis provided sputum and cough swab samples for culture. These were used to inoculate blood agar (BA) and Pseudomonas-selective media (PSM). These plates were incubated for 48 hr at 37 degrees C inside sealed plastic bags. The air surrounding the samples after 48 hr (headspace) was analyzed using SIFT-MS. PA growth was commonly associated with the production of significant quantities of VCs, notably hydrogen cyanide gas (HCN). This was detectable in the headspace of 15/22 of PA-positive samples. In contrast, it was only seen in the headspace of 1/13 control samples (6 sterile plates and 7 plates with only mixed upper respiratory tract flora). The concentration of HCN was significantly higher above PA-positive samples than above other bacterial growth (P < 0.01), and in our study, levels of HCN greater than 100 ppb were a sensitive (68%) and highly specific (100%) biomarker of PA. SIFT-MS can detect a range of VCs from PA in vitro. HCN may be a specific indicator of PA infection in vivo, and offers promise as a biomarker for noninvasive detection of PA infection by breath analysis.
    No preview · Article · May 2005 · Pediatric Pulmonology