Morinda citrifolia俗名為 noni，中文名稱為海巴戟天。果實內具有調節免疫的成分，也具有抑制肺癌及肉瘤生長的功能；將海巴戟天葉以乙醇及已烷萃取，發現萃取液具有抗氧化的活性及抗結核菌生長的成分。本研究主要是以熱水及99.5%乙醇萃取海巴戟天葉、果實、青莖、褐莖，所得到的萃取液測試oxacillin resistant Staphylococcus aureus (ORSA)、oxacillin susceptible Staphylococcus aureus (OSSA )抗菌能力。結果顯示海巴戟天果實99.5%乙醇萃取物具有抗菌的效果，最小抑制濃度(minimum inhibitory concentration, MIC)為20 mg/ml。再將果實99.5%乙醇萃取物和β-lactam類的抗生素，如oxacillin和ampicillin一起作用於ORSA和OSSA，結果微量抑制濃度指數(fractional inhibitory concentration index, FIC index)分別為0.25及0.5，表示果實99.5%乙醇萃取物和β-lactam類的抗生素具有協同作用。但是與minocycline和ofloxacin共同進行抑菌，則發現不具有協同作用。此外，也發現果實99.5%乙醇萃取物會降低ORSA及OSSA對高離子和低滲透壓的耐受性。 Noni is the common name for Morinda citrifolia L. The fruit of Noni contains immunomodulatory polysaccharide-rich substance with anti-tumor activity in the Lewis lung. The ethanolic and hexane extracts from the noni leaves exhibited antioxidative activity and antibacterial property against mycobacterium tuberculosis. In this study, the aqueous and 99.5% ethanolic crude extracts were isolated from the leaves, fruits stems of Morinda citrifolia, which were used to estimate the antibacterial activity against Staphylococcus aureus. Our results showed that the ethanolic extract from the fruits of Morinda citrifolia reveal the growth inhibitory activity against oxacillin-susceptible and oxacillin-resistant Staphylococcus aureus (OSSA and ORSA), the minimum inhibitory concentration (MIC) of the ethanolic extract from fruits against ORSA and OSSA were 20 mg/ml. Combinations of the ethanolic extract from the fruits with β-lactams, including oxacillin and ampicillin, showed the fractional inhibitory concentration (FIC) index of the tested β-lactams against ORSA and OSSA were 0.25 and 0.5, respectively. The results indicating that the ethanolic extract from the fruits synergizes the activity of β-lactams against effect against ORSA and OSSA. However, indifferent effect was observed in the combinations between the fruits ethanolic extract and minocycline or ofloxacin. The fruits ethanolic extract also reduced the tolerance of ORSA and OSSA to high ionic strength and low osmotic pressure.