Background and Objectives: The conservation of indigenous medicinal plants is of paramount importance. This study investigated two native medicinal plants from Lorestan province: Stachys lavandulifolia and Teucrium polium, both widely used in traditional medicine. T. polium is recognized for its anti-diabetic, anti-inflammatory, and antimicrobial properties, whereas S. lavandulifolia exhibits analgesic and anti-inflammatory effects, potentially serving as an effective alternative to synthetic pharmaceuticals. The objective of this research was to identify the essential oil constituents of these plants and evaluate their antimicrobial properties against four bacterial species: Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Enterococcus faecalis. Methodology: In July 2023, the aerial parts of S. lavandulifolia and T. polium were collected at full flowering stage from Zarrin Meshk Mountain (Aleshtar) and the Ivan-Dar area (Khorramabad), respectively, in Lorestan province, Iran. The plant specimens were identified, shade-dried, ground, and subjected to hydro-distillation using a Clevenger apparatus to extract their essential oils. Phytochemical characterization of the essential oil compounds was performed using Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). A bacterial suspension equivalent to the 0.5 McFarland standard (1.5×108 CFU/mL) was prepared from standard strains of human pathogenic bacteria (P. aeruginosa, E. coli, S. aureus, E. faecalis) and cultured on Mueller-Hinton Agar plates. Subsequently, 5 µL of the extracted essential oil was impregnated onto sterile blank paper discs. A control disc was impregnated with 5 µL of Dimethyl Sulfoxide (DMSO). Standard antibiotic discs, SAM (Ampicillin) and CN (Cephalexin), served as positive controls. The discs were placed onto the prepared bacterial lawns and incubated at 37°C for 24 hours. The discs containing the essential oils were then examined for the presence or absence of inhibition zones. Results: Thirty-four compounds were identified in the essential oils of both plant species. The main constituents of T. polium essential oil were Caryophyllene (25.82%), tau-Cadinol (16.91%), and α-Cadinol (9.03%), whereas the major compounds of S. lavandulifolia essential oil were β-Phellandrene (13.44%), Myrcene (13.42%), Caryophyllene (11.86%), and α-Terpineol (10.97%). Variation in essential oil composition can be attributed to multiple factors, including plant genetic structure, climatic conditions, soil characteristics, and developmental stage. In the assessment of antimicrobial effects against the four bacterial species, the essential oils of both plants exhibited non-significant inhibitory activities. However, previous studies indicate that the antimicrobial efficacy of essential oils and extracts depends on numerous factors, such as the plant’s chemical
profile, extraction methodology, bacterial species, and the geographical conditions of the plant's habitat. Conclusion: This study contributes to the improved identification of indigenous medicinal plants of Lorestan province and emphasizes the need for more comprehensive research to fully elucidate their pharmacological properties. Further investigations using plant extracts are recommended to evaluate their antimicrobial effects. |