Bactericidal Activity of Marine Algae Extracts Against Biofilm-Forming Pathogenic Bacteria

Abstract

Antibiotic-resistant bacteria are becoming more widespread and communities, necessitating the development of new strategies. Marine species are believed to be one of the possible origins of a broad range of bioactive substances that can be used to combat a wide range of biological activities. As a result, algae, especially marine brown algae and green algae, were adopted to examine their bactericidal activity towards biofilm-forming human bacterial pathogens. It was examined the extract of Sargassum aquifolium (Turner) C. Agardh (Phyophyceae) and Ulva lactuca (Chlorophyceae) for the relevant bioactive compounds either alone or in combination with commercially available antibiotics and with naturally derived antibacterial agents. Antibacterial activity was determined using disk diffusion and broth microdilution assays, and Fractional inhibitory concentration (FIC) was determined using the checkerboard broth microdilution method towards Gram-positive and Gram-negative biofilm-forming bacteria. Furthermore, using gas-chromatography-mass spectroscopy, the active compound present in the extracts was established (GC-MS). A total of 21 and 32 bioactive compounds with various chemical natures were detected using GC-MS analysis in ethanolic extracts of S. aquifolium (Turner) C. Agardh and U. lactuca n-hexane extracts, respectively. The crude ethanolic extraction S. aquifolium (Turner) C. Agardh was fractionated sequentially from less to intense polarity using the eluotropic sequence. The ethanolic extract has the maximum zone of inhibition on Listeria monocytogenes with a value of 38.00±0.17 mm, and the lowest was 10.67±0.06 mm for ethyl acetate fraction on Pseudomonas aeruginosa. Ethyl acetate fractionates showed a higher effectivity than other fractionations. The 256 μg/mL MIC value was recorded towards Staphylococcus aureus and L. monocytogenes and 512 μg/mL against Escherichia coli and P. aeruginosa. Its ethanolic extract also showed synergism with oxytetracycline on S. aureus, L. monocytogenes, and E. coli. Furthermore, the same extracts also showed synergism with tetracycline on E. coli and with erythromycin on P. aeruginosa. The extractions of U. lactuca were carried out using water and different organic solvents (ethanol, n-hexane, dichloromethane, and ethyl acetate). The antibacterial effectiveness of U. lactuca n-hexane extract against tested pathogens was the highest of any extract studied, with the minimum bactericidal concentration (MBC) and lowest minimum inhibitory concentration (MIC) values. Furthermore, n-hexane extracts have been used to increase the potency of naturally derived (from plants and aquatic organisms) compounds as well as conventional antibiotics after being augmented at sub-MIC amounts. Most studied antibiotics and natural medicines showed synergistic and additive antimicrobial effect against the tested bacterial species while used at sub-MIC levels. The bactericidal activity of S. aquifolium (Turner) C. Agardh ethanolic extract and U. lactuca n-hexane extract against human pathogenic bacteria is documented in this study. Also, it describes the combinatorial action of old-fashioned antibiotics and naturally derived bactericidal agents towards both types of bacterial pathogens. Keywords: Antibacterial; algae, extract, natural anti-bacterial agents, pathogenic bacteria