Last Month's Most Accessed Feature: Candida breath test: GC/MS possibilities

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  • Published: Feb 8, 2016
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Candidiasis testing

A breath test based on GC/MS analysis will be a promising way to diagnose oral candidiasis, say scientists in Germany following the in vitro analysis of volatiles released from cultures of four Candida species.

The most frequent infection inside the mouth is candidiasis, often called thrush, a fungal disease caused by yeasts of the genus Candida. The organism generally lives on mucous membranes or on the skin without any adverse effects but it can grow out of control to cause the infection, which has some uncomfortable symptoms. In the mouth, sore spots and a burning sensation are common.

There are a number of tests for Candida infection, based on the morphology of the colonies or biochemical, immunological or genetic features but the associated sample preparation, isolation, cell cultivation and analysis can be time consuming. Another option being considered by scientists in Germany would save time due to the fact that is requires no sample isolation or culturing.

Saskia Preissner and colleagues from Charité - University Medicine Berlin and the German Cancer Consortium have been investigating the possibility of a breath test for the diagnosis of candidiasis. The popularity of breath tests is increasing due to their non-invasive nature and the variation in the composition of the organic compounds that are released in the breath from various conditions. They have potential for the diagnosis of lung cancer, asthma and liver disease, among others.

Volatile profiling

In the proof-of-principle study, the researchers targeted the four most common pathogens that cause oral candidiasis: C. albicans, C. glabrata, C. tropicalis and C. krusei. Cultures of each were grown in the lab and the volatile compounds in the headspace were collected after 8 and 24 hours in a tube containing Tenax absorbent.

The trapped compounds were released by thermal desorption and analysed by GC/MS. Their identities were confirmed from the mass spectra and retention times and they were also measured by comparing the individual spectral intensities with those of external standards.

About 150 peaks in the chromatogram were identified and they demonstrated that the four species had different volatile profiles, all of which varied with time. Some species were notable by their absence, namely alkenes, ketones, terpenes, fatty acid esters, higher aldehydes and heterocyclic compounds. However, those that were emitted by the Candida species allowed them to be differentiated.

Breath test basis

C. albicans was identified specifically by the combined presence of 3-methyl-2-butanone and styrene whereas C. krusei was characterised by the presence of p-xylene, 2-octanone, 2-heptanone and n-butyl acetate.

For. C. tropicalis, the significant volatile compound was 1-hexanol which distinguished this organism from the other three Candida species. However, it is emitted by many other bacteria and fungal species so must be considered with care. If none of the aforementioned volatiles are detected but the oral presence of Candida species is suspected, then that points to C. glabrata.

These results are promising and might provide the basis for a breath test for candidiasis but a number of complicating factors remain. Tests in the lab could well provide different profiles to those emitted in the oral cavity due to the influence of the oral environment and the individual patient. The impact of these factors could be reduced by using more sensitive instrumentation that would uncover additional distinctive volatile compounds.

Another factor that must be considered is the timescale, especially if a method is developed for testing patients in the examination rooms or doctor surgeries. The profiles varied over time. Some of the compounds such as n-propyl acetate and ethyl-2-methylbutyrate only appeared after 24 hours of culture growth.

The predictive capability would be enhanced by extending the analysis to other Candida species that are found in the oral cavity. This is an important factor because Candida infections are often a result of more than one Candida species. Further target species should include C. dubliensis, C. famata, C. parapsilosis and C. kefyr which account for 4.4, 4.4, 3.1 and 2.6% of all Candida infections other than the common C. albicans.

The apparatus needed to collect volatiles from the breath is not complicated and a breath test should provide a significant time saving over conventional mycological testing. The research team envisage a test being used to confirm suspicions raised by visual inspection.

Related Links

Mycoses 2016, online: "Identification of signature volatiles to discriminate Candida albicans, glabrata, krusei and tropicalis using gas chromatography and mass spectrometry"

Article by Steve Down

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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