Growth Inhibition of Pathogenic Skin Bacteria Using Agarwood Leaf Extract

Chong, Kristin Hui Min (2023) Growth Inhibition of Pathogenic Skin Bacteria Using Agarwood Leaf Extract. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Plant extracts are known to exhibit a wide range of bioactivities due to their abundance of secondary metabolites, otherwise known as phytochemicals. This study aims to investigate the anti-bacterial and anti-biofilm activity of the ethanolic leaf extract of Aquilaria malaccensis (AMEE). These properties were tested against Gram-negative bacteria Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis and Gram-positive bacteria Staphylococcus aureus, using the broth microdilution, agar well diffusion, and mature biofilm assays. The broth microdilution assay indicated that AMEE possessed anti-bacterial activity against Klebsiella pneumoniae in a dose-dependent manner, with a minimum inhibitory concentration (MIC) of 3 mg/mL, with an inhibitory percentage of 84.66±1.66%. However, only partial inhibition of 51.92% was observed for Staphylococcus aureus at concentration of 3 mg/mL. No growth inhibitory effect was observed for Pseudomonas aeruginosa and Proteus mirabilis when tested with the extract. Agar well diffusion assay performed on Klebsiella pneumoniae and Staphylococcus aureus showed no inhibitory zone even at extract concentrations as high as 50 mg/mL. In the antibiofilm assay, AMEE extract showed growth inhibition in a dose dependant manner against Klebsiella pneumoniae for concentrations of 3 mg/mL and 2 mg/mL, with a percentage inhibition of 54.18±0.02% and 8.37±0.04% respectively. However, AMEE did not demonstrate anti-biofilm activity against S. aureus. Instead, the extract promoted biofilm formation for Proteus mirabilis. Finally, phytochemical analysis of the leaf extracts was conducted using Fourier Transform Infrared (FTIR) Spectroscopy Analysis to determine the phytochemicals responsible for the bioactivity of the leaf extracts. The results of the analysis showed that AMEE had multiple functional groups (O-H stretching and bending, C-H and C=C stretching and bending, C=O bending, and C-O stretching) that could be indicative of the presence of flavonoids, phenolic compounds, tannins, fatty acids, and steroids which are most likely the source of the plant extract’s anti-bacterial and anti-biofilm activity against Klebsiella pneumoniae and Staphylococcus aureus. Keywords: Aquilaria malaccensis, ethanolic leaf extract, broth microdilution, agar well diffusion, mature biofilm, Fourier Transform Infrared (FTIR) Spectroscopy