Saat ini banyak penelitian yang membuktikan bahwa bakteri staphylococcus aureus dan escherichia coli telah resisten terhadap antibiotik yang disebut multi drug resistan (mdr). bakteri tersebut menyebabkan berbagai penyakit pada manusia. maka dari itu diperlukan eksplorasi dan pengembangan antibiotik baru, salah satu sumber potensial adalah bakteri simbion spons stylissa sp. yang telah banyak dilaporkan oleh penelitian terdahulu. penelitian ini bertujuan untuk mengisolasi bakteri yang berasosiasi dengan spons stylissa sp., mengidentifikasi secara morfologi jenis bakteri spons stylissa sp., dan menentukan aktivitas daya hambat bakteri asosiasi spons stylissa sp. terhadap bakteri multidrug resistant (mdr). hasil isolat spons menghasilkan 20 bakteri murni, yang ditandai secara morfologi berdasarkan bentuk koloni, margin, warna dan elevasi. hasil pengamatan pewarnaan gram menunjukkan 15 isolat tergolong bakteri gram positif dan 5 isolat memiliki bakteri gram negatif. dari 20 isolat bakteri simbion spons terdapat 8 isolat yang menunjukkan potensi sebagai agen antimikroba. hasil pengujian aktivitas antimikroba dengan kode isolat ss02 menunjukkan zona bening 20.5 mm terhadap bakteri staphylococcus aureus dan pada kode isolat ss16 menunjukkan zona bening 15.5 mm terhadap bakteri escherichia coli. kata kunci: spons stylissa sp, multi drug resistant (mdr), pulau derawan

Currently, many studies have proven that the bacteria staphylococcus aureus and escherichia coli are resistant to antibiotics, called multi drug resistant (mdr) these bacteria cause various diseases in humans. therefore, research and development of new antibiotics is needed, a potential source is the sponge symbiont stylissa sp. which has been widely reported in previous studies. the purpose of the research was to isolate bacteria associated with stylissa sp. sponge. morphologically identify the type of stylissa sp sponge bacteria, and determine the inhibitory activity of stylissa sp sponge associated bacteria against multidrug resistant (mdr) bacteria. the results of sponge isolates produced 20 pure bacteria, which were morphologically characterized based on colony shape, margin, color and elevation, gram staining observations showed 15 isolates belonged to gram- positive bacteria and 5 isolates had gram-negative bacteria. of the 20 isolates of sponge symbiont bacteria, there are 8 isolates that show potential as antimicrobial agents. the results of antimicrobial activity testing with isolate code ss02 showed a clear zone of 20.5 mm against staphylococcus aureus bacteria and isolate code ss16 showed a clear zone of 15.5 mm against escherichia coli bacteria. keywords: spons stylissa sp. multi drug resistant (mdr), derawan island