Algal alkaloids are widely used for their pharmacological properties as antimicrobial agents. This study determined the antibacterial activities of algal alkaloid-rich extracts against isolates of multidrug-resistant Staphylococcus aureus and enterohaemorrhagic Escherichia coli (EHEC) O157, as well as the probable mode of action underlying their antibacterial effect. The total alkaloids were extracted from two Libyan brown algae, namely Sargassum hornschuchii and Cystoseira compressa and tested against six different isolates from the bacteria mentioned above using the agar-well diffusion method, and their mode of action on isolates was evaluated by several bacterial physiological indicators, including intracellular potassium ion efflux and nucleotide leakage. Also, the extracts' hemolytic activity was assessed as an indicator of their cytotoxicity on red blood cells. Although not to the same extent, both alkaloid extracts presented antibacterial activities against all tested isolates with no evidence of bacterial regrowth. The alkaloid extract from S. hornschuchii exerted the best effect on bacteria growth with minimum inhibitory concentration values ranging between 125 and 500 mg/mL. The results showed that the alkaloid extracts significantly induced a distinct release of nucleotide and potassium ions out of the cell membrane, indicating that they cause a change in the fluidity or permeability or both of the cell membrane. Moreover, the results revealed that there were very low cytotoxic effects. Therefore, algal alkaloids may contribute to the development of potential antibacterial agents in the future.

藻类生物碱由于其作为抗微生物剂的药理特性而被广泛使用。这项研究确定了富含藻类生物碱的提取物对耐多药金黄色葡萄球菌和肠出血性大肠杆菌（EHEC）O157的分离物的抗菌活性，以及它们潜在的抗菌作用方式。从两种利比亚褐藻（Sargassum hornschuchii和Cystoseira compressa）中提取总生物碱。并使用琼脂井扩散法针对上述细菌对六种不同的分离物进行了测试，并通过多种细菌生理指标（包括细胞内钾离子流出和核苷酸泄漏）评估了它们对分离物的作用方式。此外，提取物的溶血活性被评估为它们对红细胞的细胞毒性的指标。尽管程度不同，但两种生物碱提取物均对所有测试的分离物均具有抗菌活性，而没有细菌再生的迹象。霍恩链霉菌的生物碱提取物以最小的抑制浓度值在125到500 mg / mL之间对细菌的生长产生最好的作用。结果表明，生物碱提取物显着诱导了核苷酸和钾离子从细胞膜中的明显释放，表明它们引起了细胞膜的流动性或通透性的改变。此外，结果显示细胞毒性作用非常低。因此，藻类生物碱可能会在将来促进潜在抗菌剂的开发。