Phytochemicals Analysis, Antibacterial and Antioxidant Activity Evaluation of Bay Leaf (Laurus nobilis) Extract

Abstract

Bay Leaf (Laurus nobilis) is an evergreen perennial shrub that belongs to the laurel family (Lauraceae). L. nobilis is found effective against many infections from fungi, viruses, bacteria, and protozoa. The aim of this study was to determine the antibacterial and antioxidant activities of Bay Leaf (Laurus nobilis) extract against selected human pathogenic bacteria and to analyze its chemical composition. The plant leaf was collected from Addis Ababa around Piassa area. The leaf was then washed, air dried and the powder was extracted by using solvents like n hexane, methanol, chloroform and ethyl acetate. The ethyl acetate extract was subjected to column chromatography over silica gel (60-120 mesh). The structures of these compounds were characterized using 1H-NMR, 13C NMR and DEPT-135. The essential oil of L. nobilis leaf was hydrodistilled by using a Clevenger apparatus. The crude extract, isolated compounds and essential oil of the plant were tested against four Gram negative (P. aeruginosa (ATCC 27853), E. coli (ATCC 25922), S. typhimurium (ATCC 13311), K. pneumoniae (ATCC 700603)) and two Gram positive (S. aureus (ATCC 25923) and E. faecalis (ATCC 29212)) bacterial strains and also the samples were assessed for radical scavenging activity using DPPH assay. Antibacterial activities of the plant extracts were assessed using the agar disk diffusion method. The MIC and MBC test was performed for the bacteria which show the positive result in disk diffusion assay. Two compounds were furnished namely compound1and compound 2. These compounds are flavonoids. The extracted oil was analyzed by GC- MS and revealed presence of a total of 48 chemical components, accounting for 91.4 % of the total compositions. The major constitutes were; 1,8-cineole (26.3%),α-terpinyl acetate (17.1%), Methylisoleugenol (9.1%), α.-Terpineol (5.2%), and Linalool ( 4.6 %). These results showed the crude extract inhibited the growth of the test organisms in the order of magnitude of concentration from 25 mg/mL to 200 mg/mL. The maximum inhibition zone was recorded against E. faecalis (13.33± 1.52 mm), E. coli (14.33± 1.53mm) and S. typhimurium (16.00± 1,00mm).The highest activity of the isolated compound 1, compound 2 and essential oil exhibited maximum inhibition against S.aureus (13.0±1.73mm),E. coli (12.0±1.0 mm) and P. aeruginosa & K. pneumonia (12.33±0.58mm) respectively. Among the studied crude samples methanol extract of (1000 µg/mL) with % inhibition and IC50 of 94.56 and 0.02, respectively had better radical scavenging activity among the investigated samples. In the case of isolated compounds, compound 2 showed radical scavenging activity % inhibition at 77.75 and its IC50 value was 15.45. The finding of this study showed that bay leaf has considerable antimicrobial, antioxidant properties, which should be further examined with particular attention to the mechanisms of antimicrobial activity.