Detection of mycobacteria by VOC analysis of in vitro cultures using differential ion mobility spectrometry (DMS)

Differential ion mobility spectrometry (DMS) is an analytical technique to detect volatile organic compounds (VOCs) in gaseous samples at very low concentration ranges from ppb to ppt. The aim of this study was to investigate whether VOC analysis by DMS is capable of detecting Mycobacterium avium subspecies paratuberculosis (MAP). Headspaces of in vitro cultures of two different MAP strains at 1, 2, 3, 4 and 6 weeks after inoculation (each at two dilutions) were analyzed with DMS in comparison to control samples without viable bacteria ([i] blank medium, [ii] medium inoculated with heat-inactivated MAP, and [iii] sterile-filtered MAP culture broth). Furthermore, VOC patterns in the headspace over cultures of six non-tuberculous Mycobacteria species were compared to MAP-derived VOC patterns. Data analysis included peak detection, cluster analysis, identification of discriminating VOC features (Mann-Whitney U test) and different cross-validated discriminant analyses. VOC analysis resulted in up to 127 clusters, and revealed highly significant differences between MAP-strains and controls at all points in time. In addition, few clusters allowed differentiation between MAP and other non-tuberculous Mycobacteria and even between different MAP strains. Compounds have not been characterized. VOC analysis by DMS was able to identify MAP-positive samples after 1 week of in vitro growth. This study provides strong evidence that VOC-analysis of headspace over mycobacterial cultures in combination with appropriate data analysis has the potential to become a valuable method to identify positive samples much earlier than with current standard procedures.