Identification Of An Endophytic Fungus, Aspergillus Terreus Mp15 Isolated From Swietenia Macrophylla Leaves With Antibacterial And Antioxidant Activities
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Date
2015-11
Authors
Chan, Olivia Jade Yin
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
This research was aimed to study the antimicrobial activity of the endophytic
fungi previously isolated from the leaves of Swietenia macrophylla King. In the
primary screening, one out of nine endophytic fungal isolates exhibited antimicrobial
activity against at least one of the tested microorganisms. This fungal isolate was
selected for further tests and was then identified as Aspergillus terreus based on its
cultural features and molecular sequences. Based on the result obtained from the disc
diffusion assay, the ethyl acetate extract (extracellular) of this fungal isolate showed
promising and stable antibacterial activity against all the tested Gram positive
bacteria. The zones of inhibition recorded were ranged from 10.3 ± 0.4 to 13.7 ± 0.6
mm, whilst minimal inhibitory concentration (MIC) ranged from 0.75 to 2.00 mg/mL
and minimal bactericidal concentration (MBC) ranged from 2.00 to 8.00 mg/mL. The
extract was bactericidal against Bacillus subtilis, Bacillus spizizenii and
Staphylococcus aureus, while bacteriostatic against Bacillus cereus. Furthermore, the
addition of host plant extract in the fermentation broth had no significant effect on
the antibacterial activities of the endophytic fungal isolate, suggesting that it may
have its own biosynthetic pathway to produce bioactive compounds. Besides, time
kill study revealed that the antibacterial activity of the ethyl acetate extract was
concentration dependant towards S. aureus. Moreover, starting at the 4th hour of
treatment, the bacterial cells were completely killed with MIC without any regrowth
in subsequent hours. The significant bactericidal effect of extract against S. aureus
was also evidenced when viewed under scanning electron microscope. The bacterial
cells were collapsed, no longer in coccal shape and there were formation of cavities
on the cell surfaces. On the other hand, this A. terreus MP15 extract exhibited
potential antioxidant activity and also consisted of high total phenolic content.
Furthermore, on bioautography assay, it revealed that a yellow spot with retention
factor, Rf value 0.52 from this extract contributed to the antibacterial activity.
Subsequently, the yellow fraction labeled as 2a of the extract exhibited more potent
antibacterial activity as the MIC and MBC values were lowered, both ranged from
0.25 to 0.50 mg/mL. Besides, brine shrimp toxicity test also demonstrated that the
fraction was non-toxic. The gas chromatography-mass spectrometry analysis of this
yellow fraction revealed that the major compound was di-n-octyl phthalate, which
may contribute to the antibacterial and antioxidant activities of the extract. Therefore,
the extract of A. terreus MP15 can be regarded as a safer and potential source as
antibacterial and antioxidant food preservatives, as well as yellow colorant.
Description
Keywords
Endophytic Fungus