• antibacterial
• essential oil
• Salvia

The main scope of this study was to test the antimicrobial activity of the essential oils from five Salvia species using the disc diffusion assay method. The EOs of species which were tested were: S. officinalis (two different essential oils, one from branches and leaves and the other from flowers), S. dolomitica, S. patens and S. somalensis. The experiments were carried out on five ATCC certified bacteria strains, two gram-negative and three gram-positive:
• Escherichia coli (gram -) ATCC 28922
• Pseudomonas aeruginosa (gram -) ATCC 27853
• Enterococcus faecalis (gram +) ATCC 29212
• Staphylococcus aureus (gram +) ATCC 29213
• Staphylococcus epidermidis (gram +) ATCC n/a
There are some previous publications about antimicrobial activity of S. officinalis, but none of them was relating S. officinalis grown in Malta. The other species under investigation were not tested yet with disc diffusion assay on these bacteria strains.
Every essential oil was also analyzed by gas chromatography and mass spectrometry at University of Pisa in order to find out the composition.
Salvia officinalis from Argotti Botanic Garden was hydro-distilled with a Clevenger apparatus at the scene while other oils were extracted with the same technique at University of Pisa, Department of Pharmaceutical Sciences.
Each experiment was replicated three times in order to have a statistical validity.
The results of the analysis of the data were conducted with the statistical program SPSS. The program was set to make a general linear model univariate analysis: the dependent variable was the diameter of the zone of inhibition and the independent variables were trial, concentration and essential oil.
The essential oils tested displayed a certain activity against one or more bacteria, but the concentrations needed were very high in most cases. It probably cannot be possible to use them as new antibiotic agents.
Not all the oils tested showed an inhibitory effect on all the bacteria tested; for example Salvia patens was not effective at all against Pseudomonas aeruginosa. The oils which presented an antibiotic activity showed a certain trend linking concentration and zone of inhibition: the higher the concentration, the wider is the diameter of the zone of inhibition. This meant that the procedure used for testing was good.
The standard deviation between the three replicates resulted acceptable, so that repeatability was assured.