In vitro antimicrobial activity of methanol extracts from Spongia officinalis, Spongia agaricina, Aplysina aerophoba collected from the Gulf of Saros in Turkey was screened against sixteen microorganisms in this study. The antimicrobial activity was determined using agar disc diffusion method. Bacillus cereus ATCC 7064, Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25902, Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 122228, Klebsiella pneumoniae, Enterococcus faecalis, Aspergillus niger, Aspergillus fumigatus var. elipticus, Aspergillus flavus, Penicillium granulatum, Penicillium rugulosum, Penicillium jenseii, Aspergillus canditus, Geotrichum candidum and Candida albicans ATCC 10239 were used as test microorganisms. Zones of inhibition of the extracts were compared with different standard antibiotics like Ampicillin and Penicillin for antibacterial activity and Ketoconazole and Nystatin for antifungal activity. The results showed that especially Aplysina aerophoba and Spongia agaricina remarkably inhibited both bacterial and fungal growth. While antimicrobial activity was obtained from the extract of the Aplysina aerophoba against the Gram-positive bacteria, the Gram-negative bacteria and some fungi, Spongia agaricina extract exhibited antimicrobial activity against all of the test microorganisms excluding one bacterium. Hence, it has been demonstrated that a new bioactive natural product can be discovered from the two sponges in this study
