Laser pulses shred superbugs without harming human cells

Antibiotics were one of the most important inventions of the 20th century, but their effectiveness is plummeting as bacteria develop resistance to them. Now, researchers at Washington University in St. Louis have shown that ultrashort pulses of laser light can kill bacteria and viruses, without harming human cells.

Image showing proteins inside bacteria
Ultrashort laser pulses can kill viruses and antibiotic-resistant bacteria, by disrupting proteins inside them.

The rise of multidrug-resistant “superbugs” is a looming health crisis that, according to some studies, could claim up to 10 million lives per year by 2050. Our last line of defense is already beginning to fail, and some strains of bacteria are now resistant to every antibiotic in use.

New antibiotics are always in development, but that’s just kicking the problem down the road. To break the loop, scientists are investigating other methods for killing bacteria that they can’t evolve resistance to – physical attacks like jagged materials, synthetic polymers, molecular drills, liquid-metal shredders, poisoned arrow molecules, and black phosphorus coatings.

And now we might be able to add lasers to that list. The Washington researchers had previously been exploring how ultrashort pulses of laser light could kill off viruses and regular bacteria, but for the new study they investigated how well they might destroy antibiotic-resistant bacteria, as well as hard-to-kill bacterial spores.

The team turned its focus on two specific superbug species: multidrug-resistant Staphylococcus aureus (MRSA) and ESBL-producing E. coli, each representing one of the two main categories of bacteria, gram positive and gram negative. They also targeted Bacillus cereus spores, which are food-borne pathogens that can survive being boiled or cooked.

And sure enough, the laser pulses wiped out more than 99.9 percent of each microbe. The team says the technique works because the lasers excite protein structures inside viruses and bacteria, causing some of their molecular bonds to break. As the broken ends connect almost at random, protein function shuts down inside the microbe, killing them.

Importantly, the laser pulses don’t harm human cells – the team says they would need to be several orders of magnitude more powerful before they posed a threat to us. That could make them a safer disinfectant alternative to harsh chemicals, radiation or heat.

“The ultrashort-pulse laser technology uniquely inactivates pathogens while preserving human proteins and cells,” says Shaw-Wei Tsen, first author of the study. “Imagine if, prior to closing a surgical wound, we could scan a laser beam across the site and further reduce the chances of infection. I can see this technology being used soon to disinfect biological products in vitro, and even to treat bloodstream infections in the future by putting patients on dialysis and passing the blood through a laser treatment device.”

The research was published in the Journal of Biophotonics.

Written by Michael Irving

Source: Washington University in St. Louis