How to sample Listeria monocytogenes culture for volatolomics by headspace extraction-gas chromatography-Q Exactive-Orbitrap mass spectrometry?

Volatolomics - branch of metabolomics focused on volatile organic compounds (VOCs) - provides a wealth of information for characterizing foodborne pathogens and their behavior. But there is no knowledge relating on how to sample microbial VOCs. The aim of the present study was to determine the most informative sampling mode for further volatolomics. Taking Listeria monocytogenes (L. monocytogenes) as a model pathogen and using case-control experiments based on 0-24 h cultures on liquid synthetic growth medium, bacteria volatolomics was performed by headspace solid phase microextraction - gas chromatography - Q Exactive - Orbitrap ™ mass spectrometry on three types of samples: (i) the whole culture, which contains global information diluted by the growth medium, (ii) the pellet collected after centrifugation of the whole culture, which concentrates bacterial cells; and (iii) the related supernatant which includes what the bacteria released into the growth medium. Compound Discoverer ™ software was used for automatic peak deconvolution of VOCs. The three sampling modes resulted in different and complementary L. monocytogenes candidate VOC markers: whole culture and pellet together cover 83 % of the candidate markers, while supernatant and supernatant-pellet combination reveal only 59 % and 74 %, respectively. The robustness of the candidate VOC markers identified together with the relevance of combining the different sampling modes are discussed.