Antimicrobial Activity of Putative Endophytic Fungal Isolates from Leaves of Gray Mangrove (Avicennia marina) Mangrove Species in Bula Mangrove Sanctuary in General Santos City

Mangroves are not only significant in climate mitigation as carbon sinks, but also a potential solution to the growing antimicrobial resistance worldwide. This study involves the evaluation of endophytic fungal isolates from Avicennia marina mangrove leaves which are known for their production of unique biological compounds or metabolites with pharmacological activity. Fungal endophytes from A. marina leaves from Bula Mangrove Sanctuary, Barangay Bula, General Santos City, were isolated. There were four (4) putative endophytes isolated which exhibited varying antimicrobial activity against Bacillus subtilis (ATCC 6633), Escherichia coli (ATCC 25922), and Staphylococcus aureus (ATCC 25923). The isolates grown in PDB were tested using the extract source mycelia (M) and broth (B) used. It was found that against B. subtilis the zone of inhibition (ZOI) of Avicennia marina Endophyte (AME) AME3 and AME4 were very active, AMEI was active, and AME2 was partially active in inhibition. While, AMEI-B, AME2- B, AME3-B, and AME4-B have no ZOI activity, hence are inactive according to the protocol of Quinto and Santos (2005). Against E. coli, AME4-M is active, AME3-M is partially active, and AME1-M and AME2-M are inactive against. On the other hand, the AME1-B and AME3-B are partially active, while AME2-B and AME4-B have an active zone of inhibition. Lastly, inactive/no inhibition zone was observed and recorded against S. aureus among all the endophyte isolates.