Trans-cinnamaldehyde triggers stringent response-mediated virulence attenuation in pathogenic Escherichia coli

Area of Science:

• Microbiology
• Molecular Biology
• Pharmacology

Background:

• Antimicrobial resistance in Escherichia coli poses a significant threat to human and animal health.
• Novel strategies beyond conventional antibiotics are urgently needed to combat resistant E. coli strains.

Purpose of the Study:

• To investigate the potential of trans-cinnamaldehyde (t-CA) as an antimicrobial agent against E. coli.
• To elucidate the molecular mechanisms underlying t-CA's effects, particularly its interaction with the stringent response pathway.

Main Methods:

• RNA sequencing (RNA-seq) to analyze transcriptional changes induced by sub-inhibitory concentrations of t-CA.
• Measurement of (p)ppGpp alarmone levels to assess stringent response activation.
• Biofilm formation assays and cytotoxicity assessments in mammalian cell lines.
• In vitro assays using Peripheral Blood Mononuclear Cells (PBMCs) and in vivo studies using the Galleria mellonella infection model.

Main Results:

• Sub-inhibitory t-CA treatment remodels transcriptional programs, suppressing virulence factors like iron acquisition, quorum sensing, and acid resistance via the RelA-mediated stringent response.
• t-CA induces (p)ppGpp accumulation, linking stress signaling to virulence repression.
• t-CA impairs biofilm formation, reduces metabolic activity, attenuates LPS-induced cytokine production in PBMCs, and improves survival in G. mellonella.
• The observed effects were less pronounced in a relA-deficient E. coli strain, confirming RelA's crucial role.

Conclusions:

• Trans-cinnamaldehyde modulates E. coli virulence through the stringent response pathway, offering a promising antivirulence strategy.
• t-CA demonstrates potential as an adjuvant therapy to combat challenging E. coli infections, reducing reliance on traditional antibiotics.