Abstract:
The accelerating pharmaceutical problem of bacteria growing resistant to existing antibiotics forces
the scientific community to search for new antibacterial compounds for antibiotic drug development.
Literature reveals that Sri Lankan mangrove inhabiting endolichenic fungal (ELF) population is rich
in many such bioactive compounds. Previously isolated and cultured ELF, Xylaria feejeensis; from
the lichen Graphis librata inhabiting in the mangrove plant Rhizophora mucronata was cultured
on 60 large potato dextrose agar medium containing petri dishes and incubated for 14 days at
room temperature. After extracting secondary metabolites to ethyl acetate (EA) the resulted crude
extract was tested for its antibacterial and antioxidant activity. EA crude extract showed negligible
antioxidant activity in DPPH radical scavenging assay hence this assay was not proceeded further.
The activity of crude extract (5 mg/ml) against Escherichia coli (ATCC25922), Staphylococcus aureus
(ATCC25923) and Bacillus subtilis (ATCC6051) was tested using agar well diffusion antibacterial
assay. An inhibition zone diameter of 1.9 cm, 2.2 cm, and 2.2 cm against three bacterial strains with
Azithromycin positive control (5 mg/ml) 2.2 cm, 2.2 cm and 2.3 cm was observed respectively. By
partitioning of EA crude extract resulted two antibacterial active hexane and chloroform fractions
and one antibacterial inactive 60% methanol in water fraction. Hexane fraction showed the highest
antibacterial activity with inhibition diameter zone of 2.6 cm against E.coli with 2.6 cm diameter of
inhibition zone for positive control. Further purification of hexane fraction was performed by normal
phase column chromatography and 4 fractions were resulted. The highest polar fraction showed 1.4,
2.1 and 1.7 cm diameter inhibition zones of growth of E.coli, S. aureus and B. subtilis comparable with
2.2 cm Azithromycin. The other 3 fractions showed no antibacterial activity against these bacterial
strains. Results suggest that further purification of active fraction and structure elucidation might
result in new antibiotic lead compounds.
