Characterization and growth optimization of marine fungi, and antibacterial and biofilm removal activities of its extracts

Marine derived fungi known as source of bioactive compounds and many were found to produce compounds with antibacterial and biofilm removal activities. The objectives of this study are; 1) to characterize fungal isolates, 2) to study the effect of media, temperature and salinity on fungal growth, 3) to determine antibacterial activity of marine fungal extracts against food-borne bacteria; Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella typhimurium and 4) to examine biofilm removal activity of marine fungal extracts. Four fungal isolates; PR1T4, PP2L4, PR3T13 and PR5T4 isolated from Pulau Redang and Pulau Payar Marine Parks, Malaysia, were characterized using morphological and molecular identification. All isolates were subjected to study of the effect of media (PYGA, MEA and PDA), temperatures (25°C and 37°C) and salinities (0% and 15% of NaCl) on their growth. Antibacterial activity of all fungal extracts was tested against the selected bacteria using agar well diffusion assay. Test surface was done on stainless steel disc (SSD); adhesion, detachment and biofilm formation of tested bacteria. Screening of fungal extracts potential as biofilm removal agents was done against tested bacteria. The isolates were identified as Penicillium citrinum (PR1T4), Sarocladium strictum (PP2L4), Aspergillus sydowii (PR3T13) and Aspergillus species (PR5T4). All isolates responded differently on all growth media but showed general preference to Malt Extract Agar (MEA) with additional of 15% sodium chloride, while 25°C was a preferable growth temperature (p>0.05) by all isolates. All isolates (PR1T4, PP2L4, PR3T13 and PR5T4) cultured in Malt Extract Broth (MEB) displayed significantly (p<0.05) higher antibacterial activity against S. aureus (16.36±0.36mm, 27.57±0.81mm, 22.60±0.62mm and 15.82±0.49mm, respectively) and L. monocytogenes (21.45±0.21mm, 22.34±0.78mm, 21.30±0.50mm and 17.27±0.38mm, respectively) compared to cultures on other media. Ethyl acetate (EA) was the best extraction solvent as crude extracts gave significantly (p