Libmonster ID: BY-1552
Author(s) of the publication: Igor USHAKOV, Natalia NOVIKOVA, Sergei SHASHKOVSKY

by Igor USHAKOV, Corresponding Member of the Russian Academy of Sciences, full member of the Russian Academy of Medical Sciences (RAMS), director of the RAS Institute of Biomedical Problems, Natalia NOVIKOVA, Dr. Sc. (Biol.), head of the laboratory "Microbiology of Environmental Conditions and Antibacterial Defense" of the same institute, Sergei SHASHKOVSKY, Cand. Sc. (Tech.), sector head of the Research Institute of the Power Engineering Industry of Bauman Moscow State Technical University

Unfortunately, the degree of biological hazards in the contemporary world is on the increase. The reason for this situation is not only in the variability of the existing microbes, but also in the emergence of new bacteria, viruses and fungi resistant to disinfection and antibiotics. It takes place also against the background of weaker human immunity. The current situation calls for radically new universal methods of infection control.

Naturally far from all microorganisms pose a threat for people. On the one hand, a number of bacteria and fungi coexist peacefully with man and even take an active part in his biological cycle. On the other hand, it is microbes that provoke regular attacks of cholera, plague, yellow fever, malaria and other diseases. In this last decade this list was supplemented with HIV, atypical pneumonia, bird and swine flu, drug-resistant forms of tuberculosis, etc. Besides, if approximately 1,000 agents of infection were known by the middle of the 20th century, more than 1,200 are on the list today.

These factors should be also taken into account by medical experts. According to the World Health Organization, hospital infections proper appear in developed countries at least among 5 percent of

стр. 11

Biodamages in a space station:

a--growth of mold fungi on a viewport;

b--growth of mold fungi on the wire insulation of a communication device;

c,d--biocorrosion of a smoke detector needle.

patients. For example, in the USA up to 2 m1n diseases of such kind are registered at in-patient clinics (with as many as 98,000 patients dying); in the FRG there are 500-700,000 and in Hungary 100,000 cases, or about 1 percent of the population of those countries.

One of the main reasons for a high level of infection like that is in the unknown hospital strains of microorganisms characterized by multiple drug resistance and possessing a high acquired resistance towards a number of traditional agents of disinfection. These factors act against the background of the already mentioned weaker trend in non-specific body defenses among the planet's population as a whole due to contamination of the environment and changes in the living conditions (hypodynamia, stress, the adverse effects of noise, vibration, electromagnetic field, etc. on human organism).

A huge economic and social damage caused by such diseases to society (for example, it makes up 5-10 bln dollars annually only in the USA) promoted the development of a new trend in modern medicine, namely, epidemiology and prevention of hospital infections, which gained world recognition in the 1970s.

But this problem is topical not only for medical institutions on the Earth. It is also needed to secure the infection safety of crews and reliable operation of space engineering (it can break down due to the destructive effect of microorganisms) in manned space missions.

Another complication is that since the time needed for interplanetary flights (Earth-Mars-Earth, etc.)* and for the creation of lunar modules increases, the sanitation-and-epidemiological conditions within manned vehicles get worse as well. For example, longtime missions within orbital complexes pose the risk of microflora in the process of crew exchanges and goods delivery. On the other hand, the use of most of the known chemical disinfectants and physical disinfection methods in the airtight living space is fraught with toxicological and ecological danger (the reasons will be discussed just below).

The long-term observations have proved that the microbiological factor is the worst possible hazard in orbital stations. It can affect adversely both the health status of people and the reliable performance of equipment. For example, in the living space of the International Space Station (ISS) there were found a great deal of bacterial and fungal species, many of them potentially pathogenic for man or conducive to polymer biodestruction and metal biocorrosion; their amount may reach the critical values 105-106 of colony-forming units in 1 m3 of the air or per 100 cmof the surface. The analysis of the microflora and equipment of the orbital complexes Salyut, Mir and

See: E. Galimov, "Prospects of Planetary Studies", Science in Russia, No. 6, 2004; A. Grigoryev, B. Morukov, "Mars: Ever Closer", Science in Russia, No. 1, 2011.--Ed.

стр. 12

Protein absorption spectra and DNA inactivation with the superposed radiation spectra of mercury bactericidal and pulsed xenon lamps.

ISS showed the presence of a total of about 300 species of bacteria and microscopic fungi. In the course of the operation of the Mir complex and the ISS damages and failures of different instruments and units were detected due to the growth of microorganisms, i.e. technophiles. It was also established that the cause of a premature failure in a communication instrument was the growth of mold fungi, and a high-strength quartz window and a fire suppression gauge went out of commission due to the attack of mold fungi and spore-forming bacteria.

Therefore, both in space engineering and in practical medicine it is important to develop new disinfection agents of rooms to increase disinfection efficiency with a simultaneous decrease in toxicity, the time and labor intensity. But before discussing them, we shall consider the action of conventional disinfectants on a microbial cell. For example, chlorine-containing preparations or hydrogen dioxide interreact with its proteins causing an oxidation reaction. Mineral acids and alkali aided by hydrogen and hydroxyl ions induce hydrolysis. Phenol preparations stimulate a protein coagulation reaction. In other words, a cell is inactivated by highly concentrated toxic substances. But since metabolism in microbes and higher animals, including man, is basically similar, all chemical disinfectants are toxic for man, which hampers their wide use, first of all, in airtight rooms.

The physical methods of disinfection (bactericidal ultraviolet radiation, strong electric fields, and the like) do not imply the use of chemical agents, do not produce harmful substances in air or water and are, therefore, ecologically clean disinfection technologies.

The bactericidal UV method is the simplest one. What is its operating principle?

Bactericidal radiation is a part of the ultraviolet spectrum and is positioned between the visible and X-ray regions in the wavelength range from 400 to 9 nm. Photobiology (subdiscipline which studies the regularities and mechanism of light action on different systems) and medicine consider the effect of ultraviolet radiation on biological objects, which passes freely through the atmosphere, i.e. from 190 to 400 nm. Depending on the biological effects in this UV range, it is divided into three main parts: long-wave (315-400 nm), medium-wave (erythema radiation, 280-315 nm) and short-wave (bactericidal radiation <280 nm) ranges.

It should be remembered that the law of photochemistry and photobiology says that only absorbed light produces effect. But the main components of all living beings, i.e. proteins, nucleic acids and lipids, are targets for quanta of short-wave ultraviolet light. Besides, in living cells this light is absorbed mainly by nucleic acids contained in DNA and proteins. The numerous experiments have shown that four kinds of photochemical damage of DNA by short-wave ultraviolet radiation are liable to occur, which cause death to microorganisms. First, it is photodimerization, i.e. linkage of two equal molecules under exposure to light. Secondly, it is photohydration, a process of addition of a water molecule or hydroxyl bases (OH-) with double bond breaking (unlike dimerization this reaction is not pho-toreversible). Thirdly, it is photocrosslinking with proteins, i.e. formation of chemical bonds of nucleic acids of DNA with protein. And, at last, it is photosplitting of DNA chains.

стр. 13

Pulsed xenon lamps and their radiation spectrum.

Today actually all ultraviolet disinfecting facilities are equipped with mercury or amalgam lamps of continuous light emission which irradiate mainly one line of 254 nm in the bactericidal spectral region (about 80 percent of the total light generated by lamp). The mechanism of such monochromatic radiation is well studied, i.e. under its action thymine dimers* are formed in DNA, and that causes death of microorganisms.

It should be noted that each type of photochemical damage depends on absorbed photon energy. But the radiation spectrum of a mercury lamp (254 nm) almost agrees with the maximum absorption of nucleic acids of DNA (265 nm). Consequently, in order to intensify the destruction processes of a microbial cell it is necessary to expand the spectral range of a light flux, first of all, in the short-wave region and, at the same time, to increase its intensity for additional activation of the proceeding photochemical reactions.

These requirements are realized in our new pulsed plasma-optical technology for disinfection of different objects. It is based on pulsed radiation of a constant spectrum (similar in composition to a solar spectrum) including its infrared, visible and ultraviolet regions. Treatment of contaminated (infected) objects is performed by several short (from dozens to hundreds of microseconds) light pulses of a very high intensity (above 10 kW/cm2) exceeding dozens of thousands times the intensity of the most powerful mercury bactericidal lamps. Besides, the frequency of pulse succession is adjusted from single exposure on the object to hundreds of bursts per second in continuous operation.

A pulsed xenon lamp in the form of a quartz tube with tungsten electrodes serves as a generator of such radiation. When high voltage is applied to the electrodes, the interelectrode gap is broken down, and a powerful electric arc discharge occurs. The formed dense xenon plasma with a temperature of 10,000-20,000 K and concentration of electrons of 1018-1019 cm3 is a source of a powerful thermal radiation in the visible and ultraviolet ranges, which is characterized by a constant spectrum. To realize the pulsed plasma-optical technology we developed designs of lamps and their operation modes in the air medium without forced cooling.

The new disinfection method exercises a destructive influence on all vital structures of microorganism cells (nucleic acids, proteins, biomembranes, etc.), which decreases their adaptation potential and increases substantially the biocidal effect. Expansion of the radiation spectrum range (200-350 nm) allows to cause photochemical damages of DNA accompanied by photodimerization, photohydration, photocrosslinking with proteins and even its chain breaking. On the wavelength less than 240 nm protein is denaturated, enzymic activity and processes of light and dark reactivation (ability of cells to correct chemical damages and breaks in DNA molecules) are suppressed.

Due to the high radiation intensity of xenon lamps the role of chain destruction reactions with the implication of radical particles intensifies many times. Besides, at the levels of radiation fluxes from 1 to 5 kW/cm2 the photothermal processes of cell destruction are triggered. In intervals dozens of microseconds long the temperature jumps can reach hundreds of degrees, which enhances the disinfection effectiveness of objects

Thymine is 5-methyluracil, a natural organic compound, contained in all organisms as part of DNA.--Ed.

стр. 14

Pulsed ultraviolet radiation acting on fungal microflora.

located in proximity to a light source. By changing the frequency of its operation it is possible to dose an ultraviolet energy flux coming to the object and to control the disinfection temperature.

The new technology agrees fully with the criteria of ecological purity and security, it requires no disinfec-tive agents and has no negative side effects (ozone and nitrogen oxides are not produced, and no ionizing component of electromagnetic radiation is present). The usable lamps contain no mercury and other toxic chemical substances.

Comparative experiments proved that pulsed ultraviolet radiation of xenon lamps acted more effectively on stable forms of microorganisms (bacteria, fungus spores) than continuous radiation of mercury lamps did. In particular, the threshold surface energy doses (bactericidal flux per 1 cm2 of the irradiated surface) of the pulsed ultraviolet radiation are 7 to 10 times below the respective doses of continuous radiation of mercury lamps. Besides, the limiting values of the disinfection effectiveness for surfaces and air by a pulsed lamp are one or two orders higher than those obtained in operation of a mercury lamp for more than 1 hour.

To make an objective assessment of the proposed sterilization method, research in the biocidal activity of pulsed ultraviolet radiation was carried out on the basis of relevant research institutes of the RAS, RAMS, Rospotrebnadzor (Federal Inspectorate for Protection of Consumers) and the Federal Biomedical Agency of the Russian Federation. As a result, a database was formed of threshold doses for above 100 species of microorganisms including 43 species isolated from the living space of the orbital space stations and above 20 highly resistant (hospital strains) species isolated from hospital wards. Disinfection effectiveness values as high as 99.9 percent to 100 percent were proved for all microflora species.

The new method of sterilization is already carried out in practice. The Melitta research and production enterprise (Moscow) has developed and mastered the manufacture of portable, mobile and stationary pulsed ultraviolet setups of the Alpha series for rapid disinfection of rooms in medical and preventive treatment facilities. By means of such plants it is possible to carry out prompt disinfection during breaks between surgical operations without decreasing the number of patients and to maintain the minimal microbial background throughout the working day. For example, the Alpha-1 setup needs only 3.5 minutes for sterilization of 100 mof air with the efficiency of 99 percent.

A high fungicidal activity of such setups provides not only for disinfection of air contaminated by bacterial spores and mold fungi, but also for prompt decontamination of open surfaces. They are also effective against the tuberculosis agent. For example, a 100 percent death of irradiated cultures was recorded upon treatment of each of 10 drug-resistant strains isolated from patients with different forms of this infectious disease.

Remote control is also important, as it provides for a higher level of biological safety of the personnel in emergency situations connected with a high concentration of pathogenic and potentially pathogenic microorganisms in rooms.

Alpha setups are operating in 39 regions of Russia and also in the USA, Israel and the Republic of South Africa. More than 500 mobile and portable plants are used in polyclinics, maternity hospitals and other medical and preventive treatment facilities of the Russian

стр. 15

Mobile Alpha-01, portable Alpha-05 and stationary Alpha-02 setups for rapid disinfection of rooms.

Ministry of Health and Social Security and that has greatly decreased the level of hospital infections. For example, in 2007-2008 the monitoring of medical treatment institutions of the Altai Territory equipped with pulsed ultraviolet setups showed a 25-27 percent drop in purulent and septic infections among newborn babies and women in labor. Taking into account that about 10 percent of hospital deaths is not due to the main disease, but is caused by purulent and septic complications, it is obvious that saving the life of each fourth patient in this risk area is an important contribution to practical public health.

To sum up, just an example from space activities. The use of the pulsed ultraviolet equipment in sterilization of rooms in the Baikonur launching area has decreased essentially the probability of transmission of pathogenic agents by the aerogenic way during communication of cosmonauts with accredited representatives of mass media, members of the State Commission and of the Cosmonaut Training Center. The treatment of cosmonauts' personal kits and goods by the Alpha setup before delivery to the International Space Station has increased the efficiency of the sanitary-hygienic and antiepidemic maintenance of space flights.

A team of research scientists (headed by Igor Ushakov) has merited an award of the Russian Federation's government in the field of science and technology in 2010 for the development and introduction of pulsed plasma-optical technologies and setups into space and practical medicine. These are Igor Ushakov, director of the RAS Institute of Medicobiological Problems; Natalia Novikova and Nikolai Polikarpov, research scientists of the same institute; Alexander Kamrukov and Sergei Shash-kovsky of Bauman State Technical University; Yakov Goldstein, director of the Melitta R&D enterprise; Mikhail Shandala, director of the Desinfectology Institute, and Viktor Yuzbashev of the same institute; Vyacheslav Rogozhnikov, deputy head of the Federal Medicobiological Agency.


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Igor USHAKOV, Natalia NOVIKOVA, Sergei SHASHKOVSKY, STERILIZING LIGHT // Minsk: Belarusian Electronic Library (BIBLIOTEKA.BY). Updated: 23.09.2021. URL: https://biblioteka.by/m/articles/view/STERILIZING-LIGHT (date of access: 27.10.2021).

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