Quantification of methyl thiocyanate in the headspace of Pseudomonas aeruginosa cultures and in the breath of cystic fibrosis patients by selected ion flow tube mass spectrometry

Abstract

Infection by Pseudomonas aeruginosa (PA) is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Breath analysis could potentially be a useful diagnostic of such infection, and analyses of volatile organic compounds (VOCs) emitted from PA cultures are an important part of the search for volatile breath markers of PA lung infection. Our pilot experiments using solid-phase microextraction, SPME and gas chromatography/mass spectrometric (GC/MS) analyses of volatile compounds produced by PA strains indicated a clear presence of methyl thiocyanate. This provided a motivation to develop a method for real-time online quantification of this compound by selected ion flow tube mass spectrometry, SIFT-MS. The kinetics of reactions of H(3)O(+), NO(+) and O(2)(+•) with methyl thiocyanate at 300 K were characterized and the characteristic product ions determined (proton transfer for H(3)O(+), rate constant 4.6 × 10(-9) cm(3) s(-1); association for NO(+), 1.7 × 10(-9) cm(3) s(-1) and nondissociative charge transfer for O(2)(+•) 4.3 × 10(-9) cm(3) s(-1)). The kinetics library was extended by a new entry for methyl thiocyanate accounting for overlaps with isotopologues of hydrated hydronium ions. Solubility of methyl thiocyanate in water (Henry's law constant) was determined using standard reference solutions and the linearity and limits of detection of both SIFT-MS and SPME-GC/MS methods were characterized. Thirty-six strains of PA with distinct genotype were cultivated under identical conditions and 28 of them (all also producing HCN) were found to release methyl thiocyanate in headspace concentrations greater than 6 parts per billion by volume (ppbv). SIFT-MS was also used to analyze the breath of 28 children with CF and the concentrations of methyl thiocyanate were found to be in the range 2-21 ppbv (median 7 ppbv).

Quantitative analysis of volatile metabolites released in vitro by bacteria of the genus Stenotrophomonas for identification of breath biomarkers of respiratory infection in cystic fibrosis.

“…Fourteen of these VOCs were seen in all the strains, including acetone, 2-butanone, 2-propanol, dimethyl disulphide, 2-and 3-methyl butanol. These VOCs can also be released by other bacterial cells, but in different concentration, as previously reported [5,6,12,13]. …”

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.…”

Clinical Application of Volatile Organic Compound Analysis for Detecting Infectious Diseases

“…Besides HCN, the production of methyl thiocyanate has been reported in the headspace of P. aeruginosa cultures (28 out of 36 strains), as monitored by SPME-GC-MS and real-time SIFT-MS quantification methods (94). Methyl thiocyanate was also identified with the aid of SIFT-MS in the breath samples of 28 children with CF.…”

“…Methyl thiocyanate was also identified with the aid of SIFT-MS in the breath samples of 28 children with CF. The authors of this study noted that in order to determine the clinical relevance of this VOC marker for P. aeruginosa infection, a large clinical investigation is necessary (94). A breath test involving disease-related VOC biomarkers could be a suitable tool for noninvasive diagnosis of P. aeruginosa infections (88).…”