Antibiofilm and antimicrobial assessment of naphthopyranones and other polyketides from the marine-associated fungus Aspergillus sp. SSD-A-2

Background Marine-associated fungi present a prolific source of unique natural products with interesting antimicrobial and antibiofilm activities. Methods Fungal isolate was identified using PCR via sequencing of the ITS region. Large-scale fermentation was performed on solid rice media followed by extraction with Ethyl acetate. The fungal extract was subjected to chromatographic workups to the purification utilizing high pressure liquid chromatography (HPLC). Isolated compounds were identified using HR-ESI-MS and NMR techniques. Antibacterial and antibiofilm activities of compounds 1–3 were evaluated using broth micro-dilution method (BMD) and crystal violet staining technique, respectively. Results Chemical investigation of ethyl acetate extract of a marine-associated fungus Aspergillus sp. SSD-A-2 derived from the inner tissues of the Egyptian sand dollar Mellita quinquiesperforata resulted in the isolation of one previously undescribed naphtho-α-pyrone derivative identified as (3 S )-8-carboxy-semivioxanthin ( 1 ) along with the known dimeric naphtho-α-pyrone xanthomegnin ( 2 ) and two known α-pyrone derivatives dihydroaspopyrone ( 3 ), a diastereotopic mixture of γ-lactone butanolides aspilactonols F/G ( 4 / 5 ) and 4-methyl-5,6-dihydro-2-pyranone ( 6 ). The identified compounds were evaluated for their antioxidant potential against induced mitochondrial oxidative stress model in neuroblastoma SH-SY5Y cell line. However, none of the tested compounds revealed significant activity. Compounds 1–3 exhibited biofilm inhibition percentages ranged from 79.58% to 23.68%. The test compounds induced a significant reduction in the performed biofilm optical densities in a concentration-dependent manner. Conclusions The α-pyrones and polyketides ( 1–3 ) isolated from the marine-derived fungus Aspergillus sp. SSD-A2 revealed significant and promising antibiofilm activity against three different biofilm-forming microbes at concentrations below their respective minimum inhibitory concentration values. These results indicate the importance of pursuing the search for bioactive secondary metabolites from natural, in particular, fungal sources that are considered as a repertoire of antimicrobial agents to help combatting the emerging antibiotic-resistant microbes.