Antibacterial Activity of a Laboratory-Prepared Salvia officinalis Absolute and Commercial Sage Oil against Clinical Isolates

Abstract

The increasing prevalence of multidrug-resistant bacteria necessitates the exploration of alternative antimicrobial agents. Essential oils are considered promising candidates; however, product quality and concentration can substantially influence their antimicrobial efficacy. This study compared the inhibitory activity of a laboratory-prepared *Salvia officinalis* absolute extract with that of a commercially available sage oil product against several clinical bacterial isolates and evaluated the effects of concentration and bacterial species on antibacterial activity. A total of 250 bacterial isolates were recovered from 160 clinical samples collected from four hospital wards. The sage absolute extract was prepared in the laboratory using *n*-hexane extraction followed by fractional distillation under vacuum, whereas the commercial sage oil was purchased from the local market. The disc diffusion assay was performed using concentrations of 10%, 20%, and 30% for both preparations, with an additional undiluted (100%) condition for the commercial oil. Gentamicin (10 µg) served as the positive control, while DMSO and distilled water were used as negative controls. Inhibition zones were measured after 24 h of incubation at 37°C. The chemical compositions of both preparations were determined using gas chromatography–mass spectrometry (GC–MS). The laboratory-prepared sage absolute extract exhibited moderate, concentration-dependent inhibitory activity, whereas the commercial sage oil produced no inhibition zones at any tested concentration (10%, 20%, 30%, or undiluted 100%). Inhibition zones ranged from 5.2 ± 0.4 mm against *Pseudomonas aeruginosa* at 10% to 22.4 ± 1.1 mm against *Staphylococcus aureus* at 30%. GC–MS analysis revealed that 1,8-cineole (21.4%), thujone (18.7%), and camphor (14.2%) were the major constituents of the sage absolute extract, whereas these compounds were absent or present only in trace amounts in the commercial product. Gentamicin produced inhibition zones ranging from 18 to 22 mm. Differences among concentrations and bacterial species were statistically significant (P < 0.001 and P < 0.01, respectively). The laboratory-prepared sage absolute extract demonstrated moderate antibacterial activity but was less effective than the conventional antibiotic control. The tested commercial product showed no antibacterial activity, most likely due to dilution, product degradation, or storage-related deterioration. Future studies should investigate potential synergistic effects, determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using broth microdilution methods, and evaluate potential applications in controlled environmental disinfection.