Abstract:
Majority of human pathogenic bacteria has become resistant to the exsisting antibiotics causing a
human health crisis in the world. Thus discovering novel antibacterial drug leads has become an
urgent concern. Entomopathogenic fungi (EPF) infect insects and kill or disable them. Previous
research have shown entomopathogenic fungi exhibit various bioactivities. Thus, the objective of the
current study was to isolate entomopathogenic fungi from a beetle, a Harmonia sp. in Sri Lanka and
evaluvate their potential of producing antibacterial compounds. EPF were isolated from surface
sterilized insect cadavers collected from Balangoda area in Sri Lanka. Isolated fungi were grown in
potato dextrose agar and broth media, incubated close to sporulation, harvested and extracted into
ethyl aceate. The obtained weights of the crude extracts of solid and liquid cultures were compared
using ANOVA. Antibacterial activity of the crude extracts were evaluated using agar disc diffusion
bioassays at 400 μg/disc, against two Gram-positive bacteria, Staphylococcus aureus (ATCC 25923),
Bacillus cereus (ATTC 11778) and two Gram-negative, Escherichia coli (ATCC 35218) and
Pseudomonas aeruginosa (ATCC 9027). The positive control used was Gentamycin and the negative
control was methanol. Seven morphologically different EPF were isolated from Harmonia sp. The
crude weights of the solid cultures were significantly higher than the crude weights of the liquid
cultures (ANOVA, p < 0.05). This result showed fungi have preferred to synthesize more metabolites
under solid culture conditions than liquid. Six out of the seven fungi showed antibacterial acitivities
against at least one bacterium tested. EPF cultures BET 06, 08 and 10 showed high inhibition zones
against the S. aureus and B. cereus. According to ANOVA there was a significant difference between
the antibacterial activities of the crude extracts (p < 0.05). None of the fungal extracts showed
activity against P. aeruginosa while BET 05, 06 and 08 showed mild activity against E. coli.
According to the microscopic characteristics the fungi were tentatively identified as belong to
Penicillium and Aspergillus species. A bioautography study reveled the presence of several bioactive
compounds in BET 05, 06, 08 and 10 extracts. The results of this study showed that
entomopathogenic fungi are potential sources for isolating antibacterial compounds.
Keywords: Antibacterial; Entomopathogenic fungi; Harmonia sp.; Penicillium; Aspergillus
