Antimicrobial and Anti-Biofilm Potential of Selected Plant Essential Oils against Salmonella enterica Serovar Typhimurium

Background: Salmonella enterica serovar Typhimurium is a major foodborne pathogen with growing resistance to antibiotics. Plant-derived essential oils (EOs) have emerged as potential alternatives due to their antimicrobial and anti-virulence properties. This study aimed to investigate the antibacterial, anti-biofilm, and quorum sensing (QS) inhibitory effects of EOs derived from Thymus daenensis and Satureja hortensis.
Materials & Methods: The antibacterial activity of the EOs was evaluated by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using standard microbiological assays. Biofilm inhibition and disruption were assessed via crystal violet staining. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the chemical composition of the EOs. Real-time PCR was performed to measure the expression of QS-related genes.
Findings: Both EOs exhibited antibacterial activity against S. Typhimurium, with MICs of 6.25 µg/mL (T. daenensis) and 12.5 µg/mL (S. hortensis) and MBCs of 25 µg/mL for both. GC-MS analysis revealed carvacrol, thymol, γ-terpinene, p-cymene, and α-terpinene as major constituents. At sub-MIC concentrations, T. daenensis EO inhibited biofilm formation by 68% and disrupted mature biofilms by 54%, while S. hortensis EO showed 45 and 37% inhibition, respectively. Both EOs significantly downregulated QS-related genes, indicating strong anti-QS activity.
Conclusion: The EOs derived from T. daenensis and S. hortensis exhibited strong antibacterial, anti-biofilm, and anti-QS properties against S. Typhimurium. These findings support their potential as natural therapeutic agents for combating resistant Salmonella infections.