Antibacterial Activities of Boesenbergia stenophylla (Jerangau Merah) against Selected Waterborne Bacteria

Emmanuelle Usun, Stephen (2025) Antibacterial Activities of Boesenbergia stenophylla (Jerangau Merah) against Selected Waterborne Bacteria. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Boesenbergia stenophylla is a critically endangered ginger native to the highlands of Borneo and has been traditionally used as herbal medicine. Nevertheless, there is a scarcity of information regarding the specific components of ginger and the techniques used to extract and preserve the bioactive compounds of B. stenophylla rhizome and leaf parts. Thus, the objectives of this study were to identify the chemical constituents of ethyl acetate, ethanolic and methanolic leaf and rhizome extracts via Gas Chromatography-Flame Ionization Detector (GC-FID) and Gas Chromatography-Mass Spectrometry (GC-MS), while evaluating their antibacterial activities. In this study, soxhlet extraction with ethyl acetate, ethanol and methanol were utilized to produce crude extract from rhizomes and leaves of B. stenophylla. Then, the identities of phytochemicals in the crude extracts were then identified using GC-FID and GC-MS. The crude extracts were diluted and tested for antibacterial activities against selected waterborne bacteria, namely Bacillus sp., Staphylococcus sp., Citrobacter sp., Enterobacter sp. and Klebsiella sp through disc-diffusion and colorimetric broth microdilution assays. From the yield extraction, the ethanolic rhizome extract has the most yield (5.817 ± 0.613 mm), followed by methanolic rhizome extract (5.329 ± 0.536 mm) and ethanolic leaf crude extract (3.387 ± 0.774 mm). Based on the GC-FID and GC-MS analysis, 72 out of 110 phytochemicals were identified for various biological effects including potential antibacterial effects in the crude extracts. From the disc-diffusion assay, ethanolic leaf crude extracts showed the largest inhibition zone against Enterobacter sp. and Citrobacter sp. with average diameters of 21.6 ± 0.3 mm and 20.0 ± 0.6 mm, respectively. This is followed by methanolic rhizome crude extract against Bacillus sp. (16.3 ± 0.8 mm). These crude extracts were tested in the colorimetric broth microdilution assay where the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ethyl acetate rhizome extract against Bacillus sp. were identified as low as 0.781 μg/μL. The MIC/MBC ratio of ethanolic and methanolic B. stenophylla extracts tested were found to be less than 4, which indicates the extracts can be utilized as bactericidal agents. However, the ethyl acetate crude extracts, except for rhizome extracts against Bacillus sp. and Klebsiella sp. as well as leaves extract against Klebsiella sp. showed MIC/MBC ratio same or greater than 4, suggesting the potential to be utilized as bacteriostatic agents. From this study, the crude extracts of B. stenophylla, especially ethanolic and methanolic rhizome and leaves displayed the highest extraction to treat the selected waterborne bacteria. Thus, these mentioned crude extracts should be intensively studied by purification and identification of the fractions or molecules that had potential to be used as the antibacterial agents to treat the waterborne bacteria.

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