The Antimicrobial Activity and Cellular Targets of Plant Derived Aldehydes and Degradable Pro-Antimicrobial Networks in Pseudomonas Aeruginosa

Essential oils (EOs) are plant-derived products that have been long exploited for their antimicrobial activities in medicine, agriculture, and food preservation. EOs represent a promising alternative to conventional antibiotics due to the broad-range antimicrobial activity, low toxicity to human commensal bacteria, and the capacity to kill microorganisms without promoting resistance. Despite the progress in the understanding of the biological activity of EOs, many aspects of their mode of action remain inconclusive. The overarching aim of this work was to address these gaps by studying molecular interactions between antimicrobial plant aldehydes and the opportunistic human pathogen Pseudomonas aeruginosa. We initiated my project by identifying synergistically acting combinations of phytoaldehydes and using thiol-ene chemistry to incorporate the synergistic pairs into pro-antimicrobial polymers. Such polymers released phytoaldehydes upon a change in pH and humidity and controlled growth of P. aeruginosa. Next, we used a combination of transposon mutagenesis, and RNA-seq to elucidate cellular pathways targeted by p-anisaldehyde (an EO constituent from star anise) and the polyphenol from green tea epigallocatechin gallate (EGCG). The results of these experiments identified key microbial genes and associated pathways involved in response to antimicrobial plant-derived phenylpropanoids and revealed molecular mechanisms governing the synergistic effects of individual constituents within essential oils. Finally, we broadened the antimicrobial potential of the thiol-ene polymer platform by incorporating a combination of p-anisaldehyde and furaneol, which is a natural plant-derived inhibitor of quorum sensing. The treatment with furaneol/p-anisaldehyde-containing polymeric discs strongly repressed the production of pyocyanin, reduced the exoprotease activity, and effectively eradicated established P. aeruginosa biofilms. Our results will facilitate the development of polymeric systems capable of dual phytochemical delivery and controlling microbial growth without promoting antibiotic resistance. Such materials enable the high loading, efficient encapsulation, and sustained release of hydrophobic and volatile phytochemicals and could be used as antimicrobial wound dressings, sprays, surface coatings, and packaging materials