Abstract：
Antibacterial resistance causes around 1.27 million deaths annually around the globe and has been recognized as a top 3 priority health threat. Antimicrobial photodynamic therapy (aPDT) is considered a promising alternative to conventional antibiotic treatments. Algal lipid extracts have shown antibacterial effects when used as photosensitizers (PSs) in aPDT. In this work we assessed the photodynamic efficiency of lipidic extracts of microalgae belonging to different phyla (Bacillariophyta, Chlorophyta, Cyanobacteria, Haptophyta, Ochrophyta and Rhodophyta). All the extracts (at 1 mg mL-1) demonstrated a reduction of Staphylococcus aureus >3 log10 (CFU mL-1), exhibiting bactericidal activity. Bacillariophyta and Haptophyta extracts were the top-performing phyla against S. aureus, achieving a reduction >6 log10 (CFU mL-1) with light doses of 60 J cm-2 (Bacillariophyta) and 90 J cm-2 (Haptophyta). The photodynamic properties of the Bacillariophyta Phaeodactylum tricornutum and the Haptophyta Tisochrysis lutea, the best effective microalgae lipid extracts, were also assessed at lower concentrations (75 μg mL-1, 7.5 μg mL-1, and 3.75 μg mL-1), reaching, in general, inactivation rates higher than those obtained with the widely used PSs, such as Methylene Blue and Chlorine e6, at lower concentration and light dose. The presence of chlorophyll c, which can absorb a greater amount of energy than chlorophylls a and b; rich content of polyunsaturated fatty acids (PUFAs) and fucoxanthin, which can also produce ROS, e.g. singlet oxygen (1O2), when photo-energized; a lack of photoprotective carotenoids such as β-carotene, and low content of tocopherol, were associated with the algal extracts with higher antimicrobial activity against S. aureus. The bactericidal activity exhibited by the extracts seems to result from the photooxidation of microalgae PUFAs by the 1O2 and/or other ROS produced by irradiated chlorophylls/carotenoids, which eventually led to bacterial lipid peroxidation and cell death, but further studies are needed to confirm this hypothesis. These results revealed the potential of an unexplored source of natural photosensitizers (microalgae lipid extracts) that can be used as PSs in aPDT as an alternative to conventional antibiotic treatments, and even to conventional PSs, to combat antibacterial resistance.
摘要：
抗生素耐药性每年在全球范围内造成约127万人死亡，并被认为是三大优先健康威胁。抗微生物光动力疗法（aPDT）被认为是传统抗生素治疗的有希望的替代方案。藻类脂质提取物在aPDT中用作光敏剂（PS）时已显示出抗菌作用。在这项工作中，我们评估了属于不同门（Bacillariophyta，绿藻门,蓝细菌,Haptophyta,斑藻和红藻）。所有提取物（1mgmL-1）显示金黄色葡萄球菌的减少>3log10（CFUmL-1），具有杀菌活性。芽孢杆菌和半乳杆菌提取物是抗金黄色葡萄球菌的最佳门，在光剂量为60Jcm-2（芽孢杆菌）和90Jcm-2（Haptophyta）的情况下，减少>6log10（CFUmL-1）。三orornutumPhaeodactuma和鱼叶草的光动力学特性，最佳有效的微藻脂质提取物，还在较低浓度(75μgmL-1、7.5μgmL-1和3.75μgmL-1)下进行了评估，到达，总的来说,失活率高于使用广泛使用的PS获得的失活率，如亚甲基蓝和氯e6，在较低的浓度和光剂量。叶绿素c的存在，它可以比叶绿素a和b吸收更多的能量；富含多不饱和脂肪酸（PUFA）和岩藻黄质，也可以产生ROS，例如单线态氧(1O2)，当光通电时；缺乏光保护类胡萝卜素，如β-胡萝卜素，生育酚含量低，与对金黄色葡萄球菌具有较高抗菌活性的藻类提取物有关。提取物表现出的杀菌活性似乎是由于辐照的叶绿素/类胡萝卜素产生的1O2和/或其他ROS对微藻PUFA的光氧化所致，最终导致细菌脂质过氧化和细胞死亡，但是需要进一步的研究来证实这一假设。这些结果揭示了未开发的天然光敏剂（微藻脂质提取物）来源的潜力，可以用作aPDT中的PSs，作为常规抗生素治疗的替代品，甚至是传统的PS，对抗抗菌抗性。
