Abstract

Aim: To study the bactericidal activity of crude ethanolic extract and fractionations obtained from Sargassum aquifolium (Turner) C. Agardh (brown algae) towards Gram-positive bacteria and Gram-negative biofilm-forming human pathogenic bacteria.

Background: The increasing emergence of antibiotic-resistant bacteria in the hospital and community settings has led to the discovery of alternative strategies. Marine organisms are considered as one of the potential sources of diverse bioactive molecules against several biological activities. Hence, the algae, especially the marine brown algae were selected to evaluate its antibacterial activities towards biofilm-forming human pathogenic bacteria.

Objective: To restrain the drug-resistant ability of pathogenic bacteria, we checked the extract of Sargassum aquifolium (Turner) C. Agardh (Phyophyceae) for the concerned bioactive compounds.

Methods: Antibacterial activity towards both Gram-positive and Gram-negative bacteria was evaluated using disk diffusion and broth microdilution assays. Furthermore, the active compound present in the extracts was also identified using Gas-Chromatography-Mass Spectroscopy (GC-MS).

Results: A total of 21 bioactive compounds were identified using GC-MS analysis with different chemical natures. The crude ethanolic extraction was fractionated sequentially according to the eluotropic series from less to extreme polar. The highest zone of inhibition was recorded for ethanolic extract 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 fractionate showed a higher effectivity than other fractionations. An MIC value of 256 μg/mL was recorded against 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.

Conclusion: The present study reports the antibacterial activity of the S. aquifolium (Turner) C. Agardh extracts against human pathogenic bacteria. Furthermore, it also predicts the synergistic activity of selected antibiotic combinations against both selected Gram-positive and Gram-negative pathogenic bacteria.

Keywords: Antibacterial, extraction, fractionations, Sargassum aquifolium (Turner) C. Agardh, synergy, pathogens.

Graphical Abstract