In the “humanity against bacteria” arms race, bacteria are currently ahead of us. Our ancient miracle weapons, antibiotics, fail more and more frequently when germs use delicate maneuvers to protect themselves from the effects of these drugs. Some species even retreat into human cells, where they remain “invisible” to the immune system. These particularly feared pathogens include multi-resistant staphylococci (MRSA), which can cause life-threatening illnesses such as sepsis or pneumonia.
In order to hunt down germs in their hiding places and eliminate them, a team of researchers from Empa and ETH Zurich is developing nanoparticles that use a completely different mode of action from conventional antibiotics: while antibiotics have to Difficult to penetrate human cells, these nanoparticles, due to their small size and structure, can penetrate the membrane of affected cells. Once there, they can fight bacteria.
Bioglass and metal
The team of Inge Herrmann and Tino Matter used cerium oxide, a material with antibacterial and anti-inflammatory properties in its nanoparticulate form. The researchers combined the nanoparticles with a bioactive ceramic material called bioglass. Bioglass is of interest in the medical field because it has versatile regenerative properties and is used, for example, for the reconstruction of bones and soft tissues.
They then synthesized hybrids of flame-made nanoparticles, made of cerium oxide and bioglass. The particles have already been successfully used as wound adhesives, due to which several interesting properties can be used simultaneously: thanks to the nanoparticles, bleeding can be stopped, inflammation can be alleviated and wound healing can be accelerated. In addition, the new particles show significant efficacy against bacteria, while the treatment is well tolerated by human cells.
Recently, the new technology has been successfully patented. The team has now published their findings in the scientific journal Nanoscale in the “Collection of emerging researchers 2021”.
Destruction of germs
The researchers were able to show the interactions between hybrid nanoparticles, human cells and germs using electron microscopy, among other methods. If the infected cells were treated with the nanoparticles, the bacteria inside the cells began to dissolve. However, if the researchers specifically blocked the absorption of the hybrid particles, the antibacterial effect was gone.
The exact mode of action of particles is not yet fully understood. Other metals have also been shown to have antimicrobial effects. However, cerium is less toxic to human cells than, for example, silver. Scientists currently speculate that the nanoparticles affect the cell membrane of bacteria, creating reactive oxygen species that lead to the destruction of germs. Because the membrane of human cells is structurally different, our cells are not affected by this process.
Researchers believe that resistance is less likely to develop against such a mechanism. “In addition, the cerium particles regenerate over time, so that the oxidizing effect of the nanoparticles on bacteria can start again,” explains Empa researcher Tino Matter. In this way, the cerium particles could have a lasting effect.
Next, the researchers want to analyze in more detail the interactions of particles in the infection process in order to further optimize the structure and composition of nanoparticles. The objective is to develop a simple and robust antibacterial agent, effective inside infected cells.
Delicate germs Among bacteria, some particularly sneaky pathogens enter cells and are therefore invisible to the immune system. This is how they survive times when the body’s defense is on alert. This phenomenon is also known for
staphylococci. They can be withdrawn into the cells of the skin, connective tissue, bones and even the immune system. The mechanism of this persistence is not yet fully understood.
Staphylococci are mostly harmless germs that can be found on the skin and mucous membranes. Under certain conditions, however, the bacteria flood the body and cause severe inflammation, even leading to toxic shock and sepsis. This makes staphylococci the leading cause of death from infection with a single type of pathogen.
The growing number of staphylococcal infections that no longer respond to antibiotic treatment is particularly precarious. MRSA, multi-resistant germs, are particularly feared in hospitals where, as nosocomial pathogens, they cause poorly treatable wound infections or colonize catheters and other medical equipment. In total, around 75,000 hospital infections occur each year in Switzerland, of which 12,000 are fatal.
Cerium: a jack of all trades among the chemical elements
The chemical element cerium has been wrongly named after the dwarf planet Ceres; the silver metal is currently causing a stir. As cerium oxide, it is incorporated into catalytic converters in cars, and it is also used in the manufacture of products as diverse as self-cleaning ovens, windshields and light emitting diodes (LEDs). Its antimicrobial and anti-inflammatory properties also make it interesting for medical applications.