Efficient Extraction of Essential Oils from Rosemary and Evaluation of Their Antimicrobial Activity

Abstract

Background: Rosemary (Rosmarinus officinalis L.) is an aromatic medicinal plant widely recognized for its essential oil, which contains bioactive compounds with potential antimicrobial properties. This study compared the chemical composition and antibacterial activity of naturally extracted rosemary essential oil with those of a commercially available rosemary oil against bacterial isolates recovered from a hospital environment. Methods: Rosemary essential oil was extracted from plants collected in Al-Jabal Al-Akhdar, Libya, by steam distillation. The chemical composition of the natural and commercial oils was determined using gas chromatography–mass spectrometry (GC–MS). Environmental bacterial isolates were collected from different departments of Al-Bayda Central Hospital and identified using conventional microbiological methods and 16S rRNA gene sequencing. Antibacterial activity was evaluated by agar well diffusion, while minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using the broth microdilution method. Results: The naturally extracted rosemary oil yielded 2.8% (w/w) essential oil and contained 28 identified volatile compounds. The major constituents were 1,8-cineole, camphor, α-pinene, and borneol, whereas the commercial oil showed substantially lower reported concentrations of these major constituents. The natural oil exhibited concentration-dependent antibacterial activity, with statistically significant differences among concentrations for all tested bacterial species (one-way ANOVA, all P < 0.001), while the commercial oil showed no measurable inhibition under the tested conditions. Conclusion: Naturally extracted rosemary essential oil demonstrated superior chemical quality and significantly greater in vitro antibacterial activity than the commercial preparation evaluated. These findings support further investigation of standardized rosemary essential oil as a potential complementary antimicrobial agent, although additional toxicological and in vivo studies are required before clinical application