Boiled microbes
Physicists "cooked" bacteria with a laser
Irina Usyk, "Scientific Russia" (https://scientificrussia.ru /)
Scientists from the Lebedev Physical Institute of the Russian Academy of Sciences managed to "cook" pathogenic bacteria — Staphylococcus aureus and Pseudomonas aeruginosa — using a mid-infrared laser. The experiment showed that light of this wavelength breaks the hydrogen bonds in the molecules of proteins and nucleic acids, so that the bacterium loses its activity and ability to reproduce. This method of disinfection can become a convenient option for fast contactless sterilization of products, disinfection in hospitals and food industries, and in the future, it may allow creating a portable light disinfector.
"We have shown how in practice the laser radiation of the mid-infrared range with wavelengths of three and six micrometers affects bacteria. It turned out that at the same time resonant fluctuations of molecular bonds in the main elements of the cell structure occur in the cell: in the C-N bonds of proteins and nucleic acids when exposed to radiation with a wavelength of six microns and C-H bonds of the carbon skeleton — under the influence of radiation of three microns," says Svetlana FIAN, an employee of the laboratory of Laser Nanophysics and Biomedicine Shelygina.
The widespread use of antibiotics has led to the fact that today the proportion of microorganisms resistant to them is growing in the world. Antibacterial agents are becoming less effective, so it becomes urgent to search for "physical" methods of disinfection that solve the problem of resistance of microorganisms without the use of toxic chemicals.
Chemical disinfectants destroy the superstructure of proteins and other major components of the cell wall, disrupting cellular metabolism, but they can also be toxic to humans. UV treatment leads to photolytic or photochemical damage to cell molecules: UV irradiation destroys DNA by direct exposure or through the formation of dimers of cyclobutane and pyrimidine-(6-4)-pyrimidine photoproducts. Thus, it causes DNA mutations and inactivates microorganisms.
However, ultraviolet light has a destructive effect on the DNA of mammalian cells and can provoke the development of melanoma. In addition, some types of bacteria are able to "repair" DNA by expressing the enzyme DNA photoliase, which reduces the effect of ultraviolet light to zero. Therefore, these two traditional means cannot be used everywhere, and scientists are studying other wavelength ranges.
Of great interest is the mid-infrared range, since such radiation selectively causes fluctuations in the molecular bonds of vital structures of microorganisms. Scientists have repeatedly demonstrated the harmful effects of medium IR radiation on microorganisms from heat sources, such as infrared lamps, at temperatures over 1000 degrees. The use of laser sources for these purposes can be very effective due to the high intensity of laser radiation using only the wavelength necessary for exposure.
In the course of the study, the scientists placed bacteria from cultures of Staphylococcus aureus and Pseudomonas aeruginosa on a substrate of calcium fluoride 1 millimeter thick and irradiated with femtosecond laser pulses of the mid-IR range with a wavelength of 3 and 6 microns. These wavelengths correspond to the frequencies of vibrations of the amide groups of proteins and nucleic acids (6 microns) and C-H vibrations of the carbon skeleton, the most common bond for all biopolymers (3 microns).
The pulse duration was 130 femtoseconds, the pulse energy was up to 4 microjoules, and the frequency was 1 kilohertz. Then the scientists obtained dynamic spectra of the optical density of bacterial radiation. For both bacterial cultures, the spectra showed a blue spectral shift and illumination of the samples in the spectral range of characteristic oscillations of the C-N and C-H bonds. C-N bonds are part of proteins and nucleic acids, whereas C-H bonds are the most common bonds in all biopolymers and are relatively evenly distributed throughout the entire volume of the bacterial cell.
"In the spectra, when hydrogen bonds are broken, a shift of bands towards shorter wavelengths is observed. This is a common phenomenon, and not only in bacterial cells. The presence of a blue shift indicates that hydrogen bonds are breaking inside the bacterium. Thus, the secondary and tertiary structure of proteins changes, denaturation occurs. At the same time, we observed a drop in the number of colony—forming units to zero," says Svetlana Shelygina.
Thus, irradiation inactivates microorganisms, destroying vital structural units of the bacterial cell: DNA, RNA, proteins and the cell wall. Proteins in bacteria are most strongly exposed to radiation, which leads to their denaturation. The observed dynamic IR laser illumination of bacterial cultures indicates the possibility of delivering radiation to a greater depth, which, as scientists suggest, will allow the use of medium IR radiation for the treatment of malignant tumors. In the future, scientists want to create a portable IR decontaminator, but this requires a sufficiently powerful compact laser source.
Such technology could be used in the food industry for non-contact disinfection of products through transparent packaging, premises and tools, in medicine for sterilization of tools and treatment of wounds, and even deep ones, since the radiation of the middle IR spectrum does not have mutagenic properties. Perhaps someday each of us will have our own portable IR disinfector, with which it will be possible to quickly sterilize any surface.
The main results were published in the journal Biomedical Optics Express (the antibacterial activity of radiation was shown, microbiological examination of samples was carried out), in Laser Physics Letters and Letters to the JETF (dynamic transmission spectra of laser pulses by a layer of bacteria were studied, for which a "blue shift" of the spectrum of the laser pulse for a sample with a layer of bacteria applied relative to a sample without bacteria was observed, which is associated with the rupture of hydrogen bonds responsible for the destruction of the secondary and tertiary structure of proteins and nucleic acids).
The news was prepared with the support of the Ministry of Science and Higher Education of the Russian Federation and the Russian Academy of Sciences.
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