Concluding Remarks on Microbial Emissions

In vitro headspace analysis by PTR-MS has shown that there are sufficient differences in the mass spectral profiles from different microbial cultures to permit rapid discrimination. Table 7.1 provides a summary of the various product ions (collated by m/z) observed, together with tentative assignments of the VOCs that give rise to these ions and the bacterial/microbial cultures that resulted in the volatile emissions. Whether the actual VOCs emitted are dependent on the growth material the microbial cultures are feeding from is uncertain and further investigations are needed to determine this. 

Although the results from the various PTR-MS studies are extremely encouraging for the use of headspace analysis above microbial cultures, the main question to address is whether current mass spectrometric analytical techniques have sufficient sensitivity to identify an infection in an asymptomatic person by the in vivo analysis of the VOCs on their breath in real-time, so that pre-emptive medicine can be administered before an infection becomes serious. Although the answer to this can only be obtained from further research, the results obtained from the in vitro studies are encouraging. 

Another important issue to address is the definitive identification of the VOCs emitted from microbial cultures, for which there has only been a limited amount of work to date. Such assignments would shed light on the metabolic processes occurring in the cultures, which are of considerable interest to microbiologists and may aid in the development of new antibiotics. However, we comment that these are not necessarily required to ascertain the type of bacterial infection, that is, a fingerprinting approach may be more than sufficient for use in discriminatory procedures. 

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