Copper oxide nanoparticles as an effective anti-biofilm agent against a copper tolerant marine bacterium, Staphylococcus lentus

Biofilm formation on antifouling coatings is a serious concern in seawater cooling systems and the maritime industry. A prolific biofilm forming strain (Staphylococcus lentus), possessing high tolerance (>1,000 µg ml−1) to dissolved copper ions (Cu++) was isolated from titanium coupons exposed in the coastal waters of Kalpakkam, east coast of India. S. lentus formed increased biofilm (p < 0.05) at 100 µg ml−1 of Cu++ ions, when compared with the untreated control. To combat biofilm formation of this strain, the efficacy of copper oxide nanoparticles synthesized from copper nitrate by varying the concentrations of hexamine and cetyl trimethyl ammonium bromide (CTAB), was investigated. Complete (100%) inhibition of biofilm formation was observed with plain CuO NP (0.5 M hexamine, uncapped) at 1,000 µg ml−1. Capping with CTAB, influenced the morphology and the purity of the synthesized CuO NPs but did not alter their surface charge. Capping reduced metal ion release from CuO NPs and their antibacterial and anti-biofilm property against S. lentus. Overall, uncapped CuO NPs were effective in controlling biofilm formation of S. lentus. Concurrent release of copper ions and contact mediated physical damage by CuO NPs offer a promising approach to tackle metal tolerant biofilm bacteria.

防污涂料表面的生物膜形成是海水冷却系统与海事行业面临的严峻问题。从印度东海岸卡尔帕卡姆近海水域中放置的钛试片上，分离得到一株高产生物膜的缓慢葡萄球菌（Staphylococcus lentus），该菌株对溶解铜离子（Cu++）的耐受性超过1000 μg·ml⁻¹。与未处理对照组相比，该菌株在100 μg·ml⁻¹的Cu++环境中生物膜形成量显著提升（p < 0.05）。为防控该菌株的生物膜形成，本研究考察了以硝酸铜为原料，通过改变六亚甲基四胺与十六烷基三甲基溴化铵（CTAB）的浓度合成的氧化铜纳米颗粒（CuO NPs）的防控效能。结果显示，当浓度达到1000 μg·ml⁻¹时，以0.5 M六亚甲基四胺合成的未包覆型纯相CuO NPs可完全抑制该菌株的生物膜形成（抑制率达100%）。经CTAB包覆修饰后，合成的CuO NPs的形貌与纯度发生变化，但表面电荷未受影响；同时包覆作用降低了CuO NPs的金属离子释放量，也削弱了其对缓慢葡萄球菌的抗菌与抗生物膜活性。综上，未包覆型CuO NPs可有效防控缓慢葡萄球菌的生物膜形成。CuO NPs通过铜离子释放与接触介导的物理损伤协同发挥作用，为应对耐金属生物膜细菌提供了极具潜力的防控策略。