In 2017, the World Health Organisation (WHO) published a list of high priority pathogens for which new antibiotics are needed in an attempt to galvanize action in fighting antibiotic resistance (ABR). If ABR is not tackled head on, we could see up to 10 million deaths each year by 2050. Therefore, with ongoing acceleration in research and innovation, it becomes evident that we must find alternatives to traditional therapies.
Two studies involving ISIS Neutron and Muon Source focused on methods vastly different from the conventional antibiotic routes to kill bacteria:
Self-assembling antimicrobial peptide
The first study, published in ACS Applied Materials and Interfaces, was done in collaboration with the University of Manchester, University of Melbourne, China University of Petroleum, and Institute Laue Langevin. Alongside ISIS scientists, the researchers studied how self-assembling antimicrobial peptides kill bacteria.
Antimicrobial peptides (AMPs) are naturally occurring molecules that kill microorganisms such as bacteria. However, researchers have highlighted that AMPs can be designed for a myriad of biomedical applications - such as smart drug delivery. A key challenge with AMPs is to allow the molecules to diffuse properly so they interact with bacteria's cell membrane, disrupt it and then eventually kill the bacteria.
To show the structural targeting of AMPs, researchers developed a group of structurally simple peptides with the structure Cx-G(IIKK)yI-NH2, where G, I and K are the amino acids glycine, isoleucine and lysine. For this study, they used y=2, and varied x between 4 and 12.
Unlike most conventional antibiotics, C8G2 and C12G2 readily kill bacteria by attacking their membranes. With the help of the small angle neutron scattering (SANS) instrument Loq, researchers were able to reveal elliptical cylinders of nanofibers that had self-assembled in the aqueous solution.
They then exposed these peptide cylinders to lipid membranes that mimic bacterial membrane walls. The researchers found that the long peptide nanofibers quickly disassembled into monomers and smaller aggregates that, as shown in the diagram below, inserted into the membranes. This membrane insertion is consistent with their efficient bacterial killing action.
ACS Appl. Mater. Interfaces 2020, 12, 50
The other study that ISIS researchers supported, published in ACS Nano, was led by Imperial College London and the Karolinska Institute, Sweden. Their approach was based on creating an artificial nanoparticle system, known as a nanoreactor. This system was inspired by the activity of white blood cells, which help to fight infection in the human body.
To create their nanoreactor, they encapsulated two enzymes, myeloperoxidase (MPO) and glucose oxidase (GOX), within a nanocompartment called a dendrimersome, as shown in A, below. This nanoreactor converted glucose to hypochlorite (otherwise known as bleach), which was then shown to be an excellent bacterium killer; destroying two WHO-listed pathogens, crucially, without using antibiotics.
Dendrimersomes have interesting properties including enhanced stability and programmable self-assembly. SANS was crucial for characterisation of the dendrimersome assembly during this work; experiments on the Sans2D instrument determined properties such as size and membrane thickness with excellent resolution.
Although both approaches are in their infancy, self-assembling lipopeptides and a dendrimersome-based nanoreactor system have great potential not just in combatting antimicrobial resistance but also in further biomedical applications. Using SANS provides invaluable insights into these, and other biological structures, showcasing it as a key tool in these areas of research.