Background Pseudomonas aeruginosa is a key respiratory pathogen with a distinctive odour in culture. An elevated level of hydrogen cyanide in the breath has been associated with the presence of P. aeruginosa in the airway, thus determining compounds specific to P. aeruginosa offers the possibility of a non-invasive diagnostic (breath) test.
Hypothesis Determining relevant to P. aeruginosa volatile compounds from sputum headspace gases offers target validation for the development of an electronic nose breath test for P. aeruginosa.
Methods Adult patients were recruited from specialist bronchiectasis and Cystic Fibrosis clinics. The gold standard for diagnosing P. aeruginosa infection was positive sputum cultures. 72 sputum samples were analysed. A sputum sample was kept in a glass vial with a cap containing septum. The septum was pierced with a solid phase microextraction (SPME) fibre allowing sampling of the headspace for 50 min at 37°C before transferring the fibre into gas chromatography mass spectrometry. AnalyzerPro software (automated peak capture software) and manual identification were used to identify relevant to P. aeruginosa specific compounds in the headspace of sputum.
Results 32 samples grew P. aeruginosa either on its own or mixed with other species. 2-nonanone was a marker of P. aeruginosa in sputum headspace gas with sensitivity of 72% and specificity of 88%. Cyanide was not detected. However, a combination of manually identified 2-nonanone with 17 other volatile compounds as identified by AnalyzerPro, increased sensitivity in detection of P. aeruginosa to 91% with specificity of 88%.
Conclusion Optimal sampling and capture protocols still need refinement: we were unable to detect the prior noted biomarker Cyanide. These data however demonstrate the potential for rapid and accurate diagnosis of P. aeruginosa infection from sputum samples. In contrast to the 48+ hour turnaround for standard microbiological culture, these results were available within 1–2 h. It also provides a library of compounds as targets to validate in a future study of breath testing.