The Production of Listeriolysin O and Subsequent Intracellular Infections by <i>Listeria monocytogenes</i> Are Regulated by Exogenous Short Chain Fatty Acid Mixtures

• Main Authors: Erica Rinehart, Julia Chapman, Yvonne Sun
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: Toxins
• Subjects: <i>Listeria monocytogenes</i>; LLO; short chain fatty acids; <i>hly</i>; aerobic; anaerobic
• Online Access: https://www.mdpi.com/2072-6651/12/4/218

<i>Listeria monocytogenes</i> is a foodborne pathogen capable of secreting listeriolysin O (LLO), a pore-forming toxin encoded by the <i>hly</i> gene. While the functions of LLO have been studied extensively, how the production of LLO is modulated by the intestinal environment, devoid of oxygen and enriched in short chain fatty acids (SCFAs), is not completely understood. Using <i>L. monocytogenes</i> strain 10403s, we found that <i>hly</i> transcription was moderately decreased by aerobic SCFA exposures but significantly increased by anaerobic SCFA exposures. Moreover, aerobic, but not anaerobic, exposure to low levels of SCFAs resulted in a significantly higher LLO activity. These results demonstrated that transcriptional and post-transcriptional regulations of LLO production were separately modulated by SCFAs and were responsive to oxygen levels. Examining isogenic mutants revealed that PrfA and SigB play a role in regulating LLO production in response to SCFAs. Effects of SCFAs were also present in the cardiotropic strain 07PF0776 but distinctly different from those in strain 10403s. For both strains, prior exposures to SCFAs altered intracellular infections in Caco-2 and RAW264.7 cells and the plaque sizes in L fibroblasts, a result confirming the ability of <i>L. monocytogenes</i> to adapt to SCFAs in ways that impact its subsequent infection outcomes.