Potential Biomarkers for Identification of Mycobacterial Cultures by Proton Transfer Reaction Mass Spectrometry Analysis

Rationale: Several mycobacterial species can produce serious infections in humans, and the treatment required depends on the infecting species. Fast identification, ideally with minimal manipulation of the infecting species, is therefore critical; here, we propose a method potentially allowing cultures to be identified by headspace analysis and use it to screen for differences between mycobacterial species based on the volatiles released during growth.

Methods: Short-chain volatile organic compound emissions from two non-tuberculosis slow growing mycobacterial species, Mycobacterium avium and Mycobacterium kansasii, and a non-pathogenic fast growing species, Mycobacterium smegmatis, in Middlebrook M7H9 culturing media were followed online with a proton transfer reaction quadrupole mass spectrometer.

Results: Measurable differences between the headspace of the two slow growing mycobacteria M. kansasii and M. avium were found, as well as differences with respect to the faster growing mycobacteria M. smegmatis. Three compounds, attributed to sulfur-containing volatiles--dimethyl sulfide, propanethiol and dimethyl disulfide--were found to be specific to M. avium.

Conclusions: Clear differences were detected in the low molecular weight volatile emissions compounds of the mycobacterial species under study, without the need for sample manipulation. Further studies with other mycobacterial species will reveal if the differences observed are specific to the species studied here. Furthermore, the use of an ion trap as a mass analyzer with the same ionization technique, allowing molecular detection over a wider molecular range, could allow the detection of additional biomarkers thus capturing a wider molecular range.