Membrane fatty acid composition as a determinant of Listeria monocytogenes sensitivity to trans-cinnamaldehyde

Abstract

trans-Cinnamaldehyde, the major compound of cinnamon essential oil, is a potentially interesting natural antimicrobial food preservative. Although a number of studies have addressed its mode of action, the factors that determine bacterial sensitivity or tolerance to trans-cinnamaldehyde are poorly understood. We report the detailed characterization of a Listeria monocytogenes Scott A trans-cinnamaldehyde hypersensitive mutant defective in IlvE, which catalyzes the reversible transamination of branched-chain amino acids to the corresponding short-chain α-ketoacids. This mutant showed an 8.4 fold extended lag phase during growth in sublethal concentrations (4 mM), and faster inactivation in lethal concentrations of trans-cinnamaldehyde (6 mM). trans-Cinnamaldehyde hypersensitivity could be corrected by genetic complementation with the ilvE gene and supplementation with branched-chain α-ketoacids. Whole-cell fatty acid analyses revealed an almost complete loss of anteiso branched-chain fatty acids (BCFAs), which was compensated by elevated levels of unbranched saturated fatty acids and iso-BCFAs. Sub-inhibitory concentrations of trans-cinnamaldehyde induced membrane fatty acid adaptations predicted to reduce membrane fluidity, possibly as a response to counteract the membrane fluidizing effect of trans-cinnamaldehyde. These results demonstrate the role of IlvE in BCFA production and the role of membrane composition as an important determinant of trans-cinnamaldehyde sensitivity in L. monocytogenes.

The branched chain aminotransferase IlvE promotes growth, stress resistance and pathogenesis ofListeria monocytogenes

“…This observation, combined with the fact that the Δ ilvE mutant still had 20-30% ai-BCFAs during growth in LDM, hints at the presence of another transaminase that can use Ile for ai-BCFA synthesis. Different from what we observed, an Lm mutant lacking ilvE in a different parental strain background was almost entirely lacking in ai-BCFAs when grown in rich medium, well under 10% of fatty acid content (14), and this could mean that Lm has several regulatory strategies for membrane homeostasis depending on the nutritional content of the growth medium. However, the amount of ai-BCFAs that we observed in the absence of IlvE was not sufficient for full virulence in a whole animal, highlighting the necessity of IlvE mediated ai-BCFA synthesis for membranes during infection.…”

“…Previously, an ilvE transposon-generated null mutant was shown to have extremely low levels of ai-BCFAs when grown in rich, undefined BHI medium (14). Therefore, we predicted that the Δ ilvE strain created for this study would have substantially lower levels of ai-BCFA when grown in a nutrient-limited medium (Fig.…”

“…As in many Gram-positive bacteria, including Staphylococcus aureus , the Lm plasma membrane is predominantly composed of branched chain fatty acids (BCFAs), a structural feature important for bacterial integrity against multiple stresses and during pathogenesis (6–14). Odd numbered (C15, C17) anteiso-BCFAs (ai-BCFAs) are the most abundant form of BCFA in the Lm membrane, and the ability of Lm to thrive in cold temperatures is due in large part to high ai-BCFA content that enhances membrane fluidity (15–17).…”

“…1A) (9). While BKD is essential for BCFA metabolism and protection from host immune defenses such as antimicrobial peptides (12, 13), the Lm BCAT IlvE is required for resistance to the compound trans -cinnamaldehyde, a small molecule with anti-microbial properties (14, 24). Additionally, the transcriptional regulator CodY, which senses BCAA and GTP levels, plays a major role in coordinating BCAA metabolism with virulence gene expression (21, 25–28).…”

Sanitizing cinnamaldehyde solutions against Pseudomonas aeruginosa biofilms formed on stainless steel surfaces

“…The cinnamaldehyde (3-phenyl-2-propenal) EO aromatic constituent is a natural antimicrobial compound that can be isolated from cinnamon. Cinnamaldehyde is Generally Recognized as Safe (GRAS) and approved for use in the food industry (Rogiers et al, 2017).…”