Life-threatening bacteria are becoming increasingly resistant to antibiotics, making the search for alternatives to antibiotics an increasingly urgent challenge. For certain applications, an alternative may be a special type of laser.
Researchers at the Washington University School of Medicine in St. Louis has found that lasers that emit ultra-short light pulses can kill multi-resistant bacteria and hardy bacterial spores. The results, available online in the Journal of Biophotonics, open up the possibility of using such lasers to destroy bacteria that are difficult to kill in other ways. Researchers have previously shown that such lasers do not damage human cells, making it possible to imagine using the lasers to sterilize wounds or disinfect blood products.
“Ultra-short pulse laser technology uniquely inactivates pathogens while preserving human proteins and cells,” said lead author Shaw-Wei (David) Tsen, MD, PhD, a director of radiology at Washington University’s Mallinckrodt Institute of Radiology (MIR). “Imagine if, before closing a surgical wound, we could scan a laser beam across the site and further reduce the chances of infection. I can see that this technology will soon be used to disinfect biological products in vitro and even to treat infections in the bloodstream. in the future by putting patients on dialysis and passing the blood through a laser treatment device. “
Tsen and senior author Samuel Achilefu, PhD, Michel M. Ter-Pogossian professor of radiology and director of MIR’s Biophotonics Research Center, have for years explored the bactericidal properties of ultra-short heart rate lasers. They have shown that such lasers can inactivate viruses and common bacteria without harming human cells. In the new study, conducted in collaboration with Shelley Haydel, PhD, professor of microbiology at Arizona State University, they expanded their research into antibiotic-resistant bacteria and bacterial spores.
The researchers trained their lasers on multiresistant Staphylococcus aureus (MRSA), which causes infections of the skin, lungs and other organs and the extended spectrum of beta-lactamase-producing Escherichia coli (E coli), which causes urinary tract infections, diarrhea and wound infections. In addition to their shared ability to make people unhappy, MRSA and E coli are very different types of bacteria that represent two distant branches of the bacterial kingdom. The researchers also looked at spores of the bacterium Bacillus cereus, which causes food poisoning and food spoilage. Bacillus spores can withstand boiling and boiling.
In all cases, the lasers killed more than 99.9% of the target organisms, reducing their number by more than 1,000 times.
Viruses and bacteria contain densely packed protein structures that can be excited by an ultra-short-pulse laser. The laser kills by causing these protein structures to vibrate until some of their molecular bonds break. The broken ends quickly attach to what they can find, which in many cases is not what they had been attached to before. The result is a root of incorrect binding inside and between proteins, and that root causes normal protein function in microorganisms to stall.
“We have previously published a paper in which we showed that laser power matters,” Tsen said. “At a certain laser power, we inactivate viruses. When you increase the power, you start inactivating bacteria. But it requires even higher power than that, and we’re talking orders of magnitude, to start killing human cells. So there’s a therapeutic window where we can adjust the laser parameters so that we can kill pathogens without affecting the human cells. “
Heat, radiation, and chemicals such as bleach are effective in sterilizing objects, but most are too harmful to be used on humans or biological products. By inactivating all kinds of bacteria and viruses without damaging cells, ultra-short pulse lasers can provide a new approach to making blood products and other biological products safer.
“Anything that comes from human or animal sources may be contaminated with pathogens,” Tsen said. “We screen all blood products before transfusing them to patients. The problem is that we need to know what we are screening for. If a new blood-borne virus shows up, like HIV did in the ’70s and’ 80s, it can get in. in the blood supply before we know it. Ultra-short pulse lasers could be a way to ensure that our blood supply is free of both known and unknown pathogens. “