EAGER: Antibacterial clay effects on pathogenic biofilms

研究者最近对杀死人类病原体的粘土的研究，包括像耐甲氧西林金黄色葡萄球菌（MRSA）这样的耐抗生素菌株，已经记录了它们的共同特征。在世界范围内，迄今为止所研究的粘土中，只有5- 10%在水化和体外测试时具有抗菌作用。大多数抗菌粘土来自热液蚀变的火山，火山流体产生含有还原金属的矿物。含铁伊利蒙石（I-S）是最常见的粘土矿物，尽管高岭土在一些样品中占主导地位。抗菌粘土矿物组合也可能含有非粘土还原的铁矿物（如黄铁矿），这些铁矿物会氧化，对细胞膜和细胞内蛋白质造成损害。关键是粘土矿物组合将水合水缓冲到pH和Eh条件下，从而释放出对抗菌过程至关重要的金属，从而允许与细菌相互作用。抗菌粘土还与细菌膜交换结构离子，从而削弱细菌的防御能力。这项研究将通过测试它们对生物膜的影响，将对抗菌过程的新理解提升到一个新的水平。人类传染病通常会形成生物膜，这是一种细菌群落，对抗生素的耐药性比测试的“自由漂浮”细菌悬浮液更强。抗菌粘土在生物膜上的有效性是支持在动物试验中进行昂贵的杀菌效果测试的重要步骤。如果抗菌粘土对生物膜有效，体内试验可能会导致设计新的抗生素耐药细菌治疗方法，在伤口敷料、医疗植入物（关节置换、导管）、动物饲料、农业病原体和抗菌建筑材料的生产中有潜在的应用。这项研究的科学目标是记录一种抗菌粘土在传染病最常见的生物膜上对广泛的浮游人类病原体的作用。与梅奥诊所（Rochester， MN）的传染病研究人员合作，研究者将制定将粘土应用于生物膜的方案，并评估导致或限制其抗菌活性的条件。将对临床分离的常见和耐药细菌菌株进行检测。研究人员已经证明，抗菌粘土释放金属（铝、铁），这些金属共同作用，破坏细胞膜和细胞内蛋白质，因此他们将监测这些金属与生物膜的相互作用。测试抗生素的标准方法必须修改，以测试天然粘土，因为矿物质，虽然释放金属，并没有完全溶解，因此会影响细菌活力的光谱评估。此外，研究人员发现，各种生长介质中的金属形态通过限制金属与细菌的反应性来影响结果。因此，在特氟龙圆盘上生长的健康生物膜将与粘土悬浮液孵育，培养物将通过连续稀释和平板计数来评估其生存能力。如果成功，该项目将弥合矿物学和医学之间的差距，促进粘土或其衍生物在抗生素耐药感染中的应用。这将加强制定医学规程，以评价能改善人类健康的矿物质。对社会的最终好处将是建立一种经济和安全的天然矿物治疗抗生素耐药感染。在伤口护理中应用抗菌活性和安全性的证明可能会导致经济地使用粘土来治疗伤口，或开发具有类似抗菌特性的新药。

Recent research by the investigator on clays that kill human pathogens, including antibiotic resistant strains like methicillin resistant S. aureus (MRSA), has documented their common characteristics. Worldwide, only 5-10 % of clays studied to date are antibacterial when hydrated and tested in vitro. Most antibacterial clays are from hydrothermally altered volcanics, where volcanogenic fluids produce minerals containing reduced metals. Ferruginous illite-smectite (I-S) is the most common clay mineral, although kaolins dominate some samples. Antibacterial clay mineral assemblages may also contain non-clay reduced Fe-minerals (e.g., pyrite) that oxidize, causing damage to cell membranes and intracellular proteins. The key is that the clay mineral assemblage buffers the hydration water to pH and Eh conditions that release metals critical to the antibacterial process, allowing interaction with the bacteria. Antibacterial clays also exchange structural ions with the bacterial membrane that weaken bacterial defenses. This research will take this new understanding of the antibacterial process, to the next level by testing their effect on biofilms. Infectious diseases in humans commonly form biofilms, which are communities of bacteria more resistant to antibiotics than the "free floating" bacterial suspensions tested. The effectiveness of antibacterial clay on biofilms is an important step in supporting the costly testing of the bactericidal effect in animal trials. If antibacterial clay is effective against biofilms, in vivo testing may lead to design of new treatments for antibiotic resistant bacteria, with potential applications in wound dressings, medical implants (joint replacements, catheters), animal feed stocks, agricultural pathogens, and production of antibacterial building materials. The scientific goal of this research is to document the effect of an antibacterial clay previously tested against a broad spectrum of planktonic human pathogens, on biofilms most common to infectious diseases. In collaboration with infectious disease researchers at the Mayo Clinic (Rochester, MN), the investigator will develop protocols for the application of clays to biofilms and evaluate conditions that lead to, or limit, their antibacterial activity. Clinical isolates of common and antibiotic resistant bacterial strains will be tested. The investigator has demonstrated that antibacterial clays release metals (Aluminum, Iron) that act together to damage cell membranes and intracellular proteins so they will monitor the interaction of these metals with the biofilms. Standard methods for testing antibiotics must be modified for testing natural clay because the minerals, while releasing metals, are not completely dissolved and therefore will affect spectroscopic evaluations of bacterial viability. Furthermore, the investigator found that metal speciation in various growth media affect results by limiting metal reactivity with bacteria. Therefore, healthy biofilms grown on Teflon disks will be incubated with clay suspensions and cultures will be evaluated for viability by serial dilution and plate counting. If successful, this project will bridge the gap between mineralogy and medicine promoting applications of clay or its derivatives to antibiotic resistant infections. This will enhance development of medical protocols for evaluating minerals that improve human health. The ultimate benefit to society will be to establish an economical and safe natural mineral cure for antibiotic-resistant infections. Proof of the antibacterial activity and safety for applications in wound care may lead to an economic use of clays to treat wounds, or to development of new medicines that incorporate similar antibacterial properties.