FRONT PAGES: Ultrashort Pulse Lasers Kill Bacterial Spores

dWeb.News Article from Daniel Webster dWeb.News

Newswise — The search for alternative antibiotics is becoming more urgent as life-threatening bacteria become increasingly resistant to antibiotics. One type of laser may be suitable for certain applications.

Researchers from Washington University School of Medicine, St. Louis discovered that lasers emitting short pulses of light can kill hardy spores and multidrug-resistant bacteria. These findings are available online in Journal of Biophotonics. They open up the possibility of using these lasers to kill bacteria that is difficult to kill with other methods. These lasers are safe for human use.

” The ultrashort pulse laser technology uniquely inactivates disease while preserving human cells and proteins,” stated the first author Shaw Wei (David), ,, an instructor of radiology at Washington University’s Mallinckrodt Institute of Radiology . Imagine if we could scan the surgical site with a laser beam before closing it. This would further reduce the chance 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.”

Tsen and senior author Samuel Achilefu, PhD, the Michel M. Ter-Pogossian Professor of Radiology and director of MIR’s Biophotonics Research Center, have been exploring the germicidal properties of ultrashort-pulse lasers for years. These lasers are capable of inactivating viruses and other bacteria, without causing harm to human cells. The new study was conducted in collaboration Shelley Haydel (PhD), a professor at Arizona State University of microbiology. They also explored antibiotic-resistant bacteria as well as bacterial spores.

The researchers trained their lasers on multidrug-resistant Staphylococcus aureus (MRSA), which causes infections of the skin, lungs and other organs, and extended spectrum beta-lactamase-producing Escherichia coli (E. coli), which cause urinary tract infections, diarrhea and wound infections. MRSA and E.coli have the same ability to make people miserable. However, they are two different types of bacteria that represent two distinct branches of the bacterial kingdom. Researchers also examined spores from the bacterium Bacillus ceus, which can cause food poisoning and food loss. Bacillus spores can withstand boiling and cooking.

In all cases, the lasers killed more than 99.9% of the target organisms, reducing their numbers by more than 1,000 times.

Viruses, bacteria and other organisms have densely packed protein structures which can be excited with an ultrashort pulse laser. These protein structures vibrate until their molecular bonds are broken. The laser kills. Broken ends attach quickly to whatever they can find. In many cases, this is not the same thing they were attached to previously. This results in a mess of wrong linkages between and inside proteins. It causes microorganisms’ normal protein function to stop.

” We have previously published a paper that showed that the laser power is important,” Tsen stated. “A certain laser power is sufficient to activate viruses. You can activate bacteria by increasing the power. To kill human cells, however, it takes more power. We’re talking about orders of magnitude. So there is a therapeutic window where we can tune the laser parameters such that we can kill pathogens without affecting the human cells.”

Heat, radiation and chemicals such as bleach are effective at sterilizing objects, but most are too damaging to be used on people or biological products. Ultrashort pulse lasers can kill all types of bacteria and viruses, without causing damage to cells. This could be a new way to make blood products and other biological products safer.

“Anything that is derived from animal or human sources could be contaminated by pathogens,” Tsen stated. Before transferring blood products to patients, we screen them all. We need to be able to identify the type of blood product we are screening. If a new blood-borne virus emerges, like HIV did in the ’70s and ’80s, it could get into the blood supply before we know it. Ultrashort-pulse lasers could be a way to make sure that our blood supply is clear of pathogens both known and unknown.”

Tsen SWD, Popovich J, Hodges M, Haydel SE, Tsen KT, Sudlow G, Mueller EA, Levin PA, Achilefu S. Inactivation of multidrug-resistant bacteria and bacterial spores and generation of high-potency bacterial vaccines using ultrashort pulsed lasers. Journal of Biophotonics. Nov. 21, 2021. DOI: 10.1002/jbio. 202100207

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