Antimicrobial Activity of Most Abundant Marine Macroalgae of the Caribbean Coast of Costa Rica

Marine ecosystems have a very large diversity of resources, most of them still partially unknown, and a few others exploited for development of new industrial and toxicological products. Seaweeds are directly exposed and are susceptible to ambient microorganisms such as bacteria, fungi and viruses. In this study, ethanolic and acetonic extracts of 13 marine algae belong to Rhodophyceae (Galaxaura marginata, Gelidiella acerosa, Corallina officinalis, Gracilaria cervicornis, Bryothamnion triquetrum, Laurencia obtusa, Laurencia papillosa), Phaeophyceae (Dictyota mertensii, Padina gymnospora, Sargassum polyceratium) and Chlorophyceae (Codium isthmocladum, Udotea flabellum, Caulerpa racemosa) from the Caribbean Coast of Costa Rica were tested in vitro for their antibacterial and antifungal activities against different types of bacteria: one Gram positive (Staphylococcus aureus) and two Gram negative (Erwinia carotovora and Escherichia coli); and one fungus (Geotrichum candidum) using disc diffusion method. Acetonic extracts of S. polyceratium showed inhibition against all microorganisms tested. The highest inhibition activity among all the acetonic extracts was shown for S. polyceratium against S. aureus. Furthermore, the acetonic extract from S. polyceratium has shown broader activity spectrum against the entire tested organism. On the other hand, the ethanolic extract of S. polyceratium, C. racemosa and G. cervicornis were active against S. aureus, however, no significant response was found against G. candidum, E. carotovora and E. coli, when the ethanolic extracts of other species were applied. Active metabolite of S. polyceratium extract was isolated by High Performance Liquid Chromatography (HPLC) and the molecular structure was preliminarily characterized through Gas Chromatography Mass Spectrometry (GC-MS), Infrared (IR), and Ultraviolet (UV) spectroscopy.