Assessment of antibacterial and anti-biofilm activities of marine fungal epiphytes associated with red and green algae of the Kenyan coast

Marine-derived fungal epiphytes represent an important yet largely unexplored source of bioactive compounds. This study investigates the antibacterial and anti-biofilm properties of cultivable fungal epiphytes associated with red and green algae collected from a single coastal site in Kenya. A total of 330 fungal isolates were initially identified based on their morphological characteristics. Following agar-plug screening, nine active isolates have been identified through ITS-rDNA sequencing. Ethyl acetate and methanolic fungal extracts were evaluated against six multidrug-resistant microorganisms using disc diffusion, MIC, MBC, and microtiter biofilm disruption assays. The five best-performing extracts were subjected to SEM imaging, with two (Cer sp-2 and Ulr-1) further analyzed via GC-MS. Extracts from both solvents showed remarkable antibacterial effects, producing zones of inhibition that spanned between 10.00 ± 0.00 and 29.00 ± 0.00 mm. Furthermore, MIC and MBC assays revealed strong activity, with the lowest recorded values being 0.039 mg/mL and 0.156 mg/mL, respectively. Scanning electron microscopy (SEM) analysis displayed structural changes in bacterial cells, supporting a membrane-targeting mechanism of action. They also exhibited significant anti-biofilm properties (P < 0.05-0.0001) compared to the PBS-treated control. Although most biofilm reduction percentages were relatively low, the extracts displayed measurable activity in disrupting pre-formed biofilms. GC-MS identified a diverse profile of bioactive metabolites in the two representative extracts. Overall, Kenyan coastal algae harbor bioactive fungal epiphytes with promising potential to combat multidrug-resistant and biofilm-forming pathogens. Comprehensive studies are needed to discover novel therapeutic candidates in the future.