A group of scientists from Biopolis, Zhejiang University, The University of South Carolina and Nanyang Technological University [Liu et al., DOI: 10.1038/NNANO.2009.153] have shown that a novel class of core–shell nanoparticles formed by self-assembly of an amphiphilic peptide have strong antimicrobial properties against a range of bacteria, yeasts and fungi.

The nanoparticles show a high therapeutic index against Staphylococcus aureus infection in mice and are more potent than their unassembled peptide counterparts. Liu et al show that the nanoparticles can cross the blood–brain barrier and suppress bacterial growth in infected brains. Taken together, these nanoparticles are promising antimicrobial agents that can be used to treat brain infections and other infectious diseases.

Compared with fungal and bacterial infection, viral infection is the least severe in most cases. The patients usually recover with no long-term effects after treatment with conventional antiviral drugs. Bacterial infection is far more serious and progresses quickly. It may result in hearing loss, learning disability or brain damage. Despite antibiotic treatment, there is high mortality and morbidity because of the difficulty in delivering drugs across the blood–brain barrier (BBB) to the brain.

To understand the mechanism of the antimicrobial functions of the nanoparticles, the scientists investigated morphological changes of various microorganisms before and after incubation with the nanoparticles at lethal doses for various periods of time through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations.

Liu et al successfully designed and synthesized antimicrobial core–shell structured nanoparticles self-assembled from an amphiphilic peptide, and gone on to demonstrate that the formation of nanoparticles strongly enhances its antimicrobial activities.

These nanoparticles possess a broad spectrum of antimicrobial activities, which efficiently inhibit the growth of various types of gram-positive and drug-resistant gram-positive bacteria, fungi and yeast, yet induce relatively low haemolysis. In addition, they have a high therapeutic index. These peptide nanoparticles are able to suppress bacterial growth in the brain. Importantly, they do not cause significant toxicity to the major organs, indicating that these nanoparticles may provide an efficient antimicrobial agent in treating brain infections. They may also be applied to other infectious diseases such as MRSA-associated infections and C. albicans-caused brain infections.

“We are able to kill bacteria better than conventional antibiotics. By attacking the cellular structure of the microbes, our nanoparticles can be used to successfully combat persistant bacterial infections,” added IBN scientist Lihong Liu, Ph.D.