Many herbs have been studied for their pharmaceutical properties and therapeutic potential during recent years. In this context, oregano (Origanum vulgare subsp. hirtum) and rosemary (Rosmarinus officinalis L.) aromatic and medicinal plants have been assessed for antioxidant, antibacterial and antifungal properties. Although the essential oils of oregano and rosemary have a significant commercial value and their therapeutical properties have been well documented, the solid residues of the essential oil hydrodistillation process however have not been studied for their antibacterial properties, to our knowledge. Therefore, the main purpose of this study was to investigate the effect of oregano and rosemary waste solid residues of hydrodistillation process on pathogenic bacteria. More specifically, the antibacterial effect of both aromatic plants herbage before distillation (raw) and the sun-dried essential oil residue were investigated on the following bacteria: Escherichia coli, Salmonella enterica subsp. enterica, Listeria monocytogenes, Staphylococcus aureus, Bacillus subtilis, Bacillus licheniformis, and B. cereus. The raw and the solid residues were grounded and incorporated in Mueller-Hinton agar before sterilization in various concentrations (5 mg/ml, 10 mg/ml and 20 mg/ml). The medium was distributed in plates and bacteria were inoculated on the plates (3 plates per bacterium). After incubation, plates were assessed for bacteria growth. Results showed that rosemary solid residue was able to inhibit the growth of all Bacilli (B. subtilis, B. licheniformis, B. cereus) strains, while oregano solid residue was able to inhibit the growth of Listeria monocytogenes and Staphylococcus aureus, even in the minimum concentration incorporated, whereas B. cereus, in the maximum concentration. These results suggest a potential use of the solid residue from the hydrodistillation of oregano and rosemary as antimicrobial substrate.
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