AUTHOR=Kragh Martin Laage , Truelstrup Hansen Lisbeth 

TITLE=Initial Transcriptomic Response and Adaption of Listeria monocytogenes to Desiccation on Food Grade Stainless Steel

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.03132

DOI=10.3389/fmicb.2019.03132

ISSN=1664-302X

ABSTRACT=<p>The foodborne pathogen <italic>Listeria monocytogenes</italic> survives exposure to a variety of stresses including desiccation in the food industry. Strand-specific RNA sequencing was applied to analyze changes in the transcriptomes of two strains of <italic>L. monocytogenes</italic> (Lm 568 and Lm 08-5578) during desiccation [15°C, 43% relative humidity (RH)] on food grade stainless steel surfaces over 48 h to simulate a weekend with no food production. Both strains showed similar survival during desiccation with a 1.8–2 Log CFU/cm<sup>2</sup> reduction after 48 h. Analysis of differentially expressed (DE) genes (&gt;twofold, adjusted <italic>p</italic>-value &lt;0.05) revealed that the initial response to desiccation was established after 6 h and remained constant with few new genes being DE after 12, 24, and 48 h. A core of 81 up- and 73 down-regulated DE genes were identified as a shared, strain independent response to desiccation. Among common upregulated genes were energy and oxidative stress related genes e.g., <italic>qoxABCD</italic> (cytochrome aa<sub>3</sub>) <italic>pdhABC</italic> (pyruvate dehydrogenase complex) and <italic>mntABCH</italic> (manganese transporter). Common downregulated genes related to anaerobic growth, proteolysis and the two component systems <italic>lmo1172</italic>/<italic>lmo1173</italic> and <italic>cheA/cheY</italic>, which are involved in cold growth and flagellin production, respectively. Both strains upregulated additional genes involved in combatting oxidative stress and reactive oxygen species (ROS), including <italic>sod</italic> (superoxide dismutase), <italic>kat</italic> (catalase), <italic>tpx</italic> (thiol peroxidase) and several thioredoxins including <italic>trxAB</italic>, <italic>lmo2390</italic> and <italic>lmo2830</italic>. Osmotic stress related genes were also upregulated in both strains, including <italic>gbuABC</italic> (glycine betaine transporter) and several chaperones <italic>clpC</italic>, <italic>cspA</italic>, and <italic>groE</italic>. Significant strain differences were also detected with the food outbreak strain Lm 08-5578 differentially expressing 1.9 × more genes (726) compared to Lm 568 (410). Unique to Lm 08-5578 was a significant upregulation of the expression of the alternative transcription factor σ<sup>B</sup> and its regulon. A number of long antisense transcripts (lasRNA) were upregulated during desiccation including <italic>anti0605</italic>, <italic>anti0936</italic>, <italic>anti1846</italic>, and <italic>anti0777</italic>, with the latter controlling flagellum biosynthesis and possibly the downregulation of motility genes observed in both strains. This exploration of the transcriptomes of desiccated <italic>L. monocytogenes</italic> provides further understanding of how this bacterium encounters and survives the stress faced when exposed to dry conditions in the food industry.</p>