Comparative Efficacy of Cold and Hot Aqueous Extracts of Some Libyan Marine Algae in Inhibiting the Growth of Food borne Pathogenic Bacteria

Abstract

This study aimed to evaluate and compare the antibacterial activity of cold and hot aqueous extracts of six marine algal species (Ulva lactuca, Codium tomentosum, Padina pavonica, Sargassum sp.,  Hypnea sp., and Petrocladia sp.) collected from the western coast of Libya (Al-Khums and Tajoura) against three foodborne bacterial strains (Escherichia coli, Staphylococcus aureus, and Bacillus cereus), using the agar well diffusion assay. The results revealed variations in the inhibitory activity depending on the algal species, extraction method, and tested bacterial strain, with hot aqueous extracts generally outperforming cold ones in achieving larger zone of inhibition diameters. The hot extract of  Padina pavonica exhibited the highest inhibitory activity against B. cereus with a diameter of (17 ± 0.3 mm), followed by Codium tomentosum at (16 ±0.2 mm). Furthermore, both Padina pavonica and Hypnea sp. recorded the highest activity against S. aureus, with inhibition diameters of (15 ±0.4 mm) and (15 ±0.2 mm), respectively, while the hot extract of Codium tomentosum achieved the largest inhibition diameter against E. coli, reaching (14 ±0.3 mm). Gram-positive bacteria demonstrated higher sensitivity compared to E. coli, whereas Petrocladia sp. displayed the lowest overall inhibitory activity. These findings indicate that Libyan marine macro algae, particularly Padina pavonica and Codium tomentosum, represent promising sources of natural antibacterial compounds, warranting further investigations to explore their potential in food and pharmaceutical applications