Nature's Antibiotic Arsenal: Thyme and Cinnamon Oils Combat Drug-Resistant E. coli and K. pneumoniae by Suppressing Virulence Genes

Background: Multidrug-resistant (MDR) pathogens pose a serious global health threat, emphasizing the need for alternative antimicrobial strategies. Objective: This study aimed to investigate the antimicrobial, anti-virulence, and antioxidant properties of 33 essential oils against clinical isolates of Escherichia coli (n=4) and Klebsiella pneumoniae (n=2). Methodology: Clinical isolates were obtained from Kasr Al Ainy Hospital, and antimicrobial activity was assessed using disc diffusion and broth microdilution assays. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined, virulence gene expression was analysed by qPCR, antioxidant capacity was evaluated using the DPPH radical scavenging assay, and phytochemical profiles were identified via LC-MS. (Results). Thyme oil (oil 25) and cinnamon oil (oil 29) exhibited the most potent antimicrobial activity, with inhibition zones up to 26 mm. Cinnamon oil had a consistent MIC of 0.0488% against all strains, while thyme ranged from 0.0488% to 0.0975%; MBCs varied by strain. Cinnamon oil significantly downregulated fimH, ompA, iss, and luxS in E. coli, and uge, mrkA, fimH, and rmpA in K. pneumoniae. Antioxidant activity was higher in cinnamon (70.57%) than in thyme (67%). LC-MS revealed thymol and carvacrol in thyme, and cinnamaldehyde and eugenol in cinnamon.(Conclusion: These findings demonstrate that thyme and cinnamon oils act through combined antimicrobial effects, virulence suppression, and antioxidant protection, supporting their potential as natural adjuvants against MDR pathogens.