Discovery Of Antibacterial-Producing Actinobacteria From Selected Malaysian Mangrove Sediments

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dc.contributor.authorMohd Syafiq Awang
dc.date.accessioned2021-03-01T07:10:32Z
dc.date.available2021-03-01T07:10:32Z
dc.date.issued2018-09
dc.description.abstractThe rapid emergence of multi-drug resistant pathogenic bacteria has called for intensive research on the discovery of new and potent antibacterial metabolites. Actinobacteria is one of the major producers of antibacterial secondary metabolites. Among the most reliable sources for the isolation of actinobacteria are forest soil and marine sediments. Mangrove is a rich marine environment, but it is seldom explored for actinobacterial isolation. Accordingly, the present study was carried out with the main aim to isolate and screen for potential antibacterial-producing actinobacteria from mangrove sediments. The mangrove sediments were sampled from the mangrove environment located at Balik Pulau, Pulau Pinang, Malaysia. A total of 131 actinobacterial isolates were successfully isolated by using a combination of selective pre-treatment and isolation media. Preliminary screening of these isolates against five species of Gram-positive and Gram-negative bacteria using cross streak plate method showed that 54 % of the isolates were capable of producing antibacterial metabolites. Among these active isolates, 70 % have broad-spectrum antibacterial activity against both Gram-positive and Gram-negative test bacteria, 24 % have narrow-spectrum antibacterial activity against only Gram-positive bacteria and 6 % against only Gram-negative test bacteria. Five actinobacterial isolates with potent broad-spectrum antibacterial activity were selected for cultivation in three litres submerged culture fermentation using a bubble-column bioreactor. The crude fermentation broth extract was obtained through solvent extraction using ethyl acetate at 1:1 ratio and tested for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against 17 test bacteria. The lowest MIC value detected was 9.77 􀁐g/mL against the clinical isolates Pseudomonas aeruginosa, Enterococcus faecalis and Listeria monocytogenes ATCC 19114. No MBC value was recorded even at the highest test concentration of 5000 􀁐g/mL of the ethyl acetate extract. Preliminary purification of the most active actinobacterial ethyl acetate extract through column chromatography produced a total of 11 fractions. Only Fractions 1 to 4 showed antibacterial activity against clinical isolates P. aeruginosa, E. faecalis, Staphylococcus aureus, Methicilin resistant Staphylococcus aureus, Shigella boydii ATCC 9207, and Staphylococcus aureus ATCC 12600. Fraction 1 exhibited the lowest MIC and MBC values of 0.15 􀁐g/mL and 2500 􀁐g/mL, respectively against P. aeruginosa and E. faecalis. Fraction 1 was further separated using thin layer chromatography, which produced three spots. Bioautography of these spots against S. aureus ATCC 12600 showed that only one spot with Rf value of 0.88 was active. Ultra-performance liquid chromatography analysis also detected only one major peak in the chromatogram, which might be the possible metabolite of interest. One actinobacterial isolate with the most active ethyl acetate extract, namely isolate PBD-310J was selected for isolate characterization and identification. Characterization through morphological and physiological characteristics, and the 16S rRNA gene sequence showed that the isolate was a species of Streptomyces and closely related to Streptomyces praecox. Thus, the finding from this study revealed that the Malaysian mangrove sediments showed a good reservoir of antibacterialproducing actinobacteria which could be candidates for future antibacterial agent.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/11628
dc.language.isoenen_US
dc.publisherUniversiti Sains Malaysiaen_US
dc.subjectActinobacteriaen_US
dc.subjectMangrove plantsen_US
dc.titleDiscovery Of Antibacterial-Producing Actinobacteria From Selected Malaysian Mangrove Sedimentsen_US
dc.typeThesisen_US
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