Etude de l’activité antimicrobienne des extraits d’une algue marine

Abstract

Recently, there has been a great deal of interest in natural substances and bioactive compounds as alternatives to synthetic products. Seaweeds particularly red algae produce a wide variety of metabolites (polyphenols, flavonoids, carotenoids…). Considered to be active compounds with a broad spectrum of biological activities (antifungal, antibacterial, antioxidant…). The aim of this study was to assess and determine the antimicrobial activity of extracts of the red seaweed Asparagopsis armata against pathogenic microbial strains. The extraction method used is maceration in four solvents: Methanol, dichloromethane, hexane and acetone. The yield from the methanol extract was the highest. Phytochemical screening of the two extracts, methanol and dichloromethane, revealed the presence of several secondary metabolites like phenols, flavonoids, terpenoids and carotenoids. The antimicrobial activity of these two extracts was tested at different concentrations. Antibacterial testing of the studied extracts was carried out using the disc diffusion method against five bacterial strains: three gram positive (Bacillus subtilis ATCC 6633, Listeria monocytogenes ATCC 13932 and Staphylococcus aureus 639c) and two gram negative (Escherichia coli and Pseudomonas aeruginosa). Antibiograms were used as positive controls. The dichloromethane extract exhibited the best antibacterial effect with inhibitory diameters that vary between 9±0 mm and 26±0 mm. The strain L. monocytogenes was the most sensitive to both extracts at all concentrations. The strains were sensitive to some of the antibiotics tested. The method of direct contact was used to evaluate the antifungal activity against four strains: Aspergillus carbonarius M 333, Aspergillus flavus NRRL 3251, Aspergillus ochraceus ATCC 3174, Penicillium glabrum. Positive controls were tested with the antifungal Nystatin. The results showed antifungal activity, more remarkable in methanolic extract with inhibitory rates up to 100% for A. carbonarius and P. glabrum. Nystatin completely inhibited the growth of all fungi.