Changes in levels of acetaldehyde, methanol and ammonia were also observed. These compounds are not see more unique to mycobacteria and will be of limited

value as individual markers for detecting M. tuberculosis complex bacteria. Their value may increase if used in combination as components of a mycobacterial VOC profile or ‘fingerprint’. Technical difficulties also arise from the variety and size of the compounds to be investigated, which range from organic compounds to simple gases. Whereas the zNose may be used for real time detection of VOC production from bacterial cultures (Casalinuovo et al., 2006; Dawson et al., 2011), concurrent measurement of gases such as ammonia will require sophisticated analytical instrumentation not readily available to microbiology laboratories. SIFT-MS and GC-MS are large expensive instruments well suited to these types of analysis. However, although sensitive and with the ability to resolve several hundreds of compounds, they are not readily suited to field deployment. The z-nose in comparison is small, rapid and much less expensive. However, it is less able to differentiate compounds and sensitivity is lower. It has been suggested that VOC may be used to detect tuberculosis disease. Detecting mycobacterial VOC in the headspace of clinical materials or in breath

will be challenging as VOC markers produced by mycobacteria in vitro Fluorouracil may not be detected in

vivo. In addition, the relatively low concentration of such markers produced in vivo may make their detection in the presence of host VOCs difficult (Syhre et al., 2009). A more robust approach is likely to be achieved by obtaining the whole spectra of samples for TB diagnosis and subjecting these to multivariate Vitamin B12 analysis and extensive validation to derive diagnostic algorithms. The dependency of PEA production on growth of the bacteria suggests that it could be used to assist LJ-based tests for susceptibility to anti-tuberculosis drugs. However, when directly testing headspace for PEA with the zNose, large numbers of bacteria were needed, and for rapid drug resistance testing, a VOC preconcentration step or a more sensitive detection method would be required. A number of other volatile compounds have recently been reported as potential markers for M. tuberculosis complex bacteria including 1-methylnaphthalene, 3-heptanone; methylcyclododecane; 2,2,4,4,6-pentamethyl heptane (isododecane); benzene, 1-methyl-4-(1-methylethyl)-; cyclohexane, 1,4-dimethyl-; 3,5-dimethylamphetamine; butanal, 3-methyl- (isopentanal); 2-hexene; trans-anti-1-methyldecahydronaphthalene (Phillips et al., 2007); and methyl phenylacetate, methyl p-anisate, methyl nicotinate and o-phenylanisole which are metabolites of nicotinic acid (Syhre & Chambers, 2008).