Low electrical currents could help fight superbugs
Scientists have shown that currents measured in millionths of amperes kill bacteria by disrupting their outer membranes. The discovery could inspire new antimicrobial technologies that use electricity to slow the spread of antibiotic-resistant infections.
Scientists have known since the 1960s that electricity can kill or suppress the growth of bacteria. However, the growing threat posed by antibiotic-resistant superbugs in recent years has made the search for new ways to reduce the transmission of bacteria more urgent.
According to a report released by the Centers for Disease Control and Prevention (CDC) in 2019, there is
Most of the early research into the bactericidal effects of electricity involved relatively large electric currents or fields. More recently, studies suggested that a current of less than 5 thousandths of an amp applied for at least 72 hours can kill bacteria by damaging their membranes.
But it’s unclear exactly how electricity destroys bacteria, and whether even weaker currents might work as well.
Today, a team of scientists from the University of Arkansas, Fayetteville, showed that a current of less than 100 millionths of an amp, or microamps, applied for 30 minutes can kill bacteria.
The current, the researchers found, works by disrupting the membranes of bacteria, allowing proteins, ions and other small molecules to seep in and out of cells.
A voltage of less than 1.5 volts was sufficient to generate the required current. “The electrical power we used is very low,” explains Professor Yong Wang, lead author of the new study. “A household battery can provide enough energy. The same goes for a 1 square centimeter solar panel. “
The results indicate that electricity may be a convenient way to continuously sterilize items, such as doorknobs, that people touch frequently. The currents are too small to harm humans, says Professor Wang.
Scientists could also use tiny currents to prevent resistant bacterial colonies, or biofilms, from forming on the surfaces of water storage or purification facilities.
Research elements in the journal Applied and environmental microbiology.
For their experiments, the researchers used tubes containing a solution of the bacteria Escherichia coli and a pair of aluminum electrodes.
They applied a variety of techniques to compare the state of bacteria in tubes where the voltage across the electrodes was on and in tubes where it was off.
For example, they exposed bacteria to a red fluorescent dye called propidium iodide which stains DNA, making it visible under a microscope. This revealed that more propidium iodide penetrated the membranes of the bacteria and bound to their DNA after the current was applied.
The experiment shows, the researchers say, that ions and other small molecules such as amino acids have leaked into and out of cells.
Another technique, called a filtration test, has proven that even molecules as large as proteins and nucleic acids can escape from cells after their membranes have been damaged by electric current.
Researchers believe that the current can disrupt the membrane by altering the normal voltage across it, known as the membrane potential.
When they applied a fluorescent dye called MitoTracker Green to bacteria, their membranes glowed brighter after exposure to electricity. While this remains a matter of debate, the authors say, some microbiologists believe that the binding of MitoTracker Green molecules to membranes is dependent on the electrical potential of the membranes.
The researchers conclude:
“This study shows that the treatment of bacteria with [an] electric current to [less than 100 microamps] for 30 minutes caused extensive damage to the membrane and led to bidirectional leakage of ions, small molecules and proteins. Interestingly, the electrical power leading to severe membrane damage of bacteria is very low, which should facilitate the use of microampere (and low voltage) electrical current for antimicrobial applications.