Comparative assessment of microalgal fatty acids as topical antibiotics

Bacteria are increasingly resistant to common antibiotics. Certain fatty acids are effective antibacterial agents and, when compared to conventional antibiotics, have fewer incidences of bacterial resistance. Algae naturally synthesize these fatty acids and can provide a sustainable source of these antibiotics. To evaluate the antibacterial properties of fatty acids, 29 acids present in algae were tested for topical antibacterial properties on Escherichia coli and Staphylococcus aureus using surface zone inhibition assay. From the set of fatty acids showing good antibacterial activity, five representative fatty acids—capric acid (10:0), palmitoleic acid (16:1), gamma-linolenic acid [18:3 (n-6)], arachidonic acid [20:4 (n-6)], and docosadienoic acid [22:2 (n-6)]—were selected for further analysis. Algal growth conditions (light, temperature, and nutrients) were manipulated to increase the content of the selected target fatty acids in five algal species (Rhodella maculata, Phaeodactylum tricornutum, Boekelovia hooglandii, Goniochloris sculpta, and Chloridella simplex). P. tricornutum contained the highest content of the target antibacterial fatty acids, with a maximum of 206 mg g⁻¹ dry weight (dw). However, biomass productivity was low; thus, for commercial viability, initial growth should be under optimum conditions and then shifted to enhance antibacterial fatty acid content. B . hooglandii had the highest biomass productivity and a total antibacterial fatty acid content of 32.6 mg g⁻¹ dw in Erddekokt + Salze + Peptone (ESP) medium, 18 °C, 80 μmol photons m⁻² s⁻¹, and 17:7-h light/dark cycle. This study identifies fatty acids that have effective antibacterial properties and potential use as topical antibacterial products and determined growth conditions that result in algae rich in these acids.