Antibacterial and antifungal activities of some marine diatoms in culture

Non-axenic unialgal cultures of eleven marine diatoms were screened against 13 pathogenic bacteria and 8 pathogenic fungi by agar disc diffusion method. The lipophilic and aqueous extracts of 6 diatoms which showed high antibacterial activity were separately screened against the same bacterial strains and two diatoms which showed high antifungal activity were screened against the same fungal strains. Gram positive bacteria, Aspergillus niger and Cryptococcus neoformans were the most susceptible pathogens. The diatom Thallassiothrix frauenfeldii showed the highest activity. Lipophilic extracts were highly active against the pathogens tested.