Volatolomics to phenotype Listeria monocytogenes behavior: Impact of growth and acid stress

Microbial volatolomics – the analysis of volatile organic compounds (VOCs) released by microbes – provides a wealth of information for phenotyping key foodborne pathogens like Listeria monocytogenes (L. monocytogenes) in their culture medium. The present study aimed to investigate how the bacterial volatolome can reflect changes in the physiological status induced by growth of the bacteria, as well as environmental changes in its culture medium. First, the volatolome of L. monocytogenes 10403S was characterized under conventional culture conditions in a pure Tryptic Soy Broth Yeast Extract (TSBYE) synthetic medium, with an initial pH of 7.2. The volatolome was analyzed by HeadSpace Solid Phase Microextraction – Gas Chromatography – Q Exactive – Orbitrap ™ Mass Spectrometry hyphenated to an automatic deconvolution of the detected VOCs with Compound Discoverer ™ software. Fifty-one candidate VOC markers were identified, including 13 compounds that have already been associated with L. monocytogenes, some of which have a proposed mechanistic origin in relation to pathogen metabolism. Second, the effect of the bacterial growth status on the volatolome was investigated by monitoring dynamic counts and conducting volatolomics analysis at four different growth times, under pH 7.2. Eighty-one candidate markers were identified, allowing for different volatolomics profile depending on the growth time to be pointed out. Third, in order to evaluate the effect of environmental factors on the volatolome of L. monocytogenes, acidic pH cultures (5.5 and 5.2) were implemented with a volatolomic study at the same growth times as above. Forty-seven and 40 candidate markers of presence of L. monocytogenes were identified in its volatolome when the initial pH of the culture medium was set at 5.5 and 5.2, respectively. Finally, the ability of the volatolome to express the phenotypic changes of L. monocytogenes induced by its growth and its environment is discussed.