Antibacterial activity of marine-derived fungal extract against clinical and environmental Pseudomonas aeruginosa strains

Abstract

Pseudomonas aeruginosa is a dangerous opportunistic pathogen and its high resistance to traditional antibiotics prompts researchers to explore alternative strategies targeting virulence factors and bacterial growth. Among these alternatives there are marine-derived fungi, and they represent a promising source of bioactive secondary metabolites with antibacterial potential and anti-virulence properties. This study aims to evaluate the antibacterial and anti-virulence activities of marine fungal extracts against clinical and environmental strains of P. aeruginosa, and comparing them to a standard reference strain (ATCC 27853). From the isolated marine fungi three species were selected for this study: Penicillium sp. (P1), Aspergillus flavus (A2), and Aspergillus terreus (A4), and their secondary metabolites were extracted using ethyl acetate. The antibacterial activity was evaluated using disk and well diffusion techniques, determining minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC), as well as the anti-virulent effect on biofilm formation and pyocyanin production, an important virulent factor regulated by quorum sensing. The results showed moderate antibacterial activity, with MIC values of 2.5 and 5 mg/mL, while MBC values were 10 and 20 mg/mL. In contrast, diffusion tests showed weak activity, indicating limited diffusion of the compounds in the solid medium. As the most active extract, Aspergillus flavus extract (A2) was selected for studying its effect on virulence factors, where it demonstrated a strong ability in inhibiting pyocyanin production by 85 to 99% in all strains, and reducing biofilm formation in the clinical strain by 24.4% and the ATCC 27853 strain by 28.5%, while a slight increase was observed in the environmental strain by 3.7%. Finally, these results indicate that marine fungal extracts have moderate antibacterial activity and high efficacy in inhibiting virulence factors associated with the quorum-sensing system, highlighting their potential as alternative therapeutic agents that target bacterial virulence factors rather than bacterial growth.