Quantification by SIFT-MS of volatile compounds emitted by in vitro cultures of S. aureus, S. pneumoniae and H. influenzae isolated from patients with respiratory diseases

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.