Antimicrobial and Antiquorum Sensing Activity of Different Parts of Laurus nobilis L. Extracts

Since quorum sensing controls the density and pathogenesis of a wide variety of bacteria, it became inviting to test some plant extracts for their anti-quorum sensing (AQS) and antimicrobial activity. Laurus nobilis L. commonly known as bay leaf belongs to the Lauracea family. It has been a potential culinary and medicinal plant in east Mediterranean including Jordan. In this study, 24 aqueous, ethanol, butanol, hexane, chloroform and methanol extracts of L.nobilis L. leaves, bark, fruit and flowers were tested for their antiquorum sensing, antibacterial and antifungal activities. Test microorganisms included Chromobacterium violaceum for anti-quorum sensing activity. Two gram positive, two gram negative bacteria and four fungi species. Of these extracts, significant antiquorum sensing activity was associated mainly with the hexane (25mm of AQS halo) and ethanol (21 mm) flowers extracts of L.nobilis L.Other extracts showed low (10-14 mm halo) to moderate 15-20 varying degrees of antiquorum sensing activity. As for antimicrobial testing, the magnitude of activity varied in terms of the type and number of bacteria and fungi tested as well as to the degree of inhibition. Superior antifungal activity as compared with nystatin was recorded for ethanol and hexane leaf and bark extracts especially against Aspergillus fumigatus (25,23 mm inhibition zone), Aspergillus niger 21,20 and Candida albicans. 11,13 The antibacterial activity also varied among different extracts and different gram positive and negative bacterial species. To be highlighted is the superior activity of aqueous bark extract against methicillin resistant Staphylococcus aureus (25 mm) compared with penicillin G (33 mm).A moderate antibacterial activity of flowers, fruits and leaves extracts against gram negative Klebsiella pneumoniae and Salmonella typhimurium was also recorded. MICs values for both bacteria and fungi were relatively high (525-3000 µg), this is understandable since we are dealing with crude extracts. These results stress for the first time the importance of antiquorum sensing activity of L.nobilis L. extracts as an antipathogenic agents and being a possible new alternative for bacterial disease therapy. It also substantiates and validates medicinal plants use in folk medicine