The cause of death of microorganisms when exposed to ionizing radiation. Living bacterium. Concentration of microbial cells in the irradiated object

In addition to spores, which are highly resistant to ionizing radiation, highly radioresistant bacteria are known that do not form spores. Highly radioresistant bacteria are most often found among cocci. The surface of various medical products, as well as the air in the premises where these products are manufactured, can be contaminated with various bacteria, including Sarcins, which are particularly resistant to ionizing radiation. The well-known Micrococcus radiodurans, isolated from irradiated meat by Anderson et al., also belongs to cocci. Spectrophotometric analysis of the pigment of radioresistant micrococci isolated by Anderson showed that most of the pigments are carotenoids. Pigments isolated from radioresistant cells were sensitive to radiation. However, non-pigmented micrococcus variants also exhibited high radioresistance. Subsequently, the micrococcus isolated by Anderson attracted the attention of radiobiologists and was named Micrococcus radiodurance. It was more resistant not only to x-rays or gamma radiation, but also to ultraviolet irradiation. The micrococcus turned out to be 3 times more resistant to ultraviolet rays than E. coli. To delay DNA synthesis in micrococcus cells, fractions are required that are 20 times higher than those that cause a similar effect in Escherichia coli.

It can be assumed that the high radioresistance of the micrococcus is associated with a special system for repairing damage caused by radiation. The different nature of repairs of damage to Micrococcus radiodurnence resulting from ultraviolet irradiation and the action of ionizing radiation has been noted.

Highly radioresistant bacteria were isolated from dust from factories producing plastic medical devices in Denmark by Christensen et al. They were Streptococcus Faccium. It turned out that the radioresistance of different strains of the same type of microorganisms varies significantly. Thus, for most strains of Sir, faecium, a dose of 20 - 30 kGy is bactericidal, and only a few strains can withstand irradiation at a dose of 40 kGy. Strains Str. faecium isolated from dust turned out to be more radioresistant. Although most strains died when irradiated at doses from 20 to 30 kGy, some strains (4 out of 28 studied) withstood irradiation at doses up to 45 kGy.

Concentration of microbial cells in the irradiated object

One of the reasons playing significant role in the effectiveness of radiation sterilization, is the concentration of microbial cells in the irradiated object.

In 1951, Hollander et al. established that the sensitivity of bacteria to irradiation is a function of cell concentration. As the concentration in the irradiated suspension decreases, its radiosensitivity increases. 10 7 cells were the optimal concentration of bacteria at which the effect of ionizing radiation was most effective. Many researchers noted that the sterilizing effect of irradiation depends both on the fraction of irradiation and on the density and volume of the irradiated suspension (7 , 36, 75 , 141 - 143). When E. coli is irradiated with beta rays from a Van de Graaff accelerator (2 MeV ) It was found that the absolutely sterilizing dose depends only on the concentration of the irradiated suspension. There is a direct proportional relationship between the concentration of microbes and the dose that kills 100% of cells: the lower the density of the irradiated suspension, the lower the radiation dose that gives the full bactericidal effect.

Figure 2.1 - Inactivation curves of various microorganisms.

1 - M. radiodurans R; 2 - Staphylococci; 3 - Micrococci; 4 - Coryneform rod; 5 - Spores; 6 - Str. faecium.

When irradiating a culture of Escherichia coli bacteria, the sterilizing effect of gamma radiation for relatively thin suspensions (8 * 10 5 -10 8 microbial bodies per 1 ml) was achieved at a dose of 2 kGy. Irradiation of a denser microbial suspension containing 10 10 microbial bodies per 1 ml at a dose of 2 kGy did not produce a bactericidal effect. Even with irradiation at doses of 4 and 5 kGy, growth of single colonies was sometimes observed. Complete sterilization of suspensions containing 10 10 and 2 * 10 10 microbial bodies per 1 ml was achieved only with irradiation at a dose of 6 kGy. A further increase in the number of microbial bodies in 1 ml of the irradiated medium did not require an increase in the irradiation dose for a full bactericidal effect. So. a suspension of Flexner dysentery bacteria at a concentration of 7*10 10 microbial bodies in 1 ml was completely inactivated by a dose of 6 kGy. Sarcina is one of the most radioresistant microorganisms. When thick suspensions of various microorganisms, both more radioresistant and less radioresistant, were irradiated at doses of 1, 2, 4, 8 kGy and 15 kGy, a relationship was observed between a decrease in the number of surviving microorganisms and an increase in the radiation dose. The higher the radiation dose, the fewer microorganisms survived after irradiation. A complete sterilizing effect was achieved by irradiating microorganisms at a concentration of 4 * 10 10 billion microbial bodies per 1 ml at a dose of 15 kGy. This proportion also killed the most resistant microorganisms - sarcin and Bacillus subtilis.

Thus, an increase in the concentration of microorganisms in an irradiated object increases their radioresistance. This situation is true for microorganisms with different radiosensitivities.

However, the increase in radioresistance of the irradiated suspension is not a consequence of the formation of radioresistance in irradiated cells. After irradiation of thick suspensions in bactericidal doses, single individuals survive, forming colonies of microbes when sown on agar. A study of the radiosensitivity of these surviving bacteria showed that they did not become more resistant to radiation compared to the original bacterial culture. This phenomenon can occur when suspensions of microorganisms of significantly less density are irradiated. It is known in the literature under the name "tail". The study of the tails also showed that bacteria that survived irradiation at lethal doses do not have increased radiosensitivity. An explanation for the observed phenomena should be sought among the reasons causing the death of microorganisms from ionizing radiation. The most likely reason for the increase in radioresistance of microorganisms with increasing concentration is a decrease in the partial pressure of dividing cells. During cell division, the nucleus becomes more vulnerable to irradiation

ovaniya. The temperature range at which the growth of psychrophilic bacteria is possible ranges from -10 to 40 °C, and the temperature optimum ranges from 15 to 40 °C, approaching the temperature optimum of mesophilic bacteria.

Mesophiles include the main group of pathogenic and opportunistic bacteria. They grow in the temperature range 10-47 °C; the optimum growth for most of them is 37 °C.

At higher temperatures (40 to 90 °C), thermophilic bacteria develop. At the bottom of the ocean in hot sulfide waters live bacteria that develop at a temperature of 250-300 ° C and a pressure of 262 atm. Thermophiles live in hot springs and participate in the processes of self-heating of manure, grain, and hay. The presence of a large number of thermophiles in the soil indicates its contamination with manure and compost. Since manure is richest in thermophiles, they are considered an indicator of soil contamination.

The temperature factor is taken into account when carrying out sterilization. Vegetative forms of bacteria die at a temperature of 60 ° C for 20-30 minutes; spores - in an autoclave at 120 ° C under steam pressure.

Well resistant to microorganisms low temperatures. Therefore, they can be stored frozen for a long time, including at liquid gas temperature (-173 ° C).

Drying. Dehydration causes dysfunction of most microorganisms. Pathogenic microorganisms (causative agents of gonorrhea, meningitis, cholera, typhoid fever, dysentery, etc.) are most sensitive to drying. Microorganisms protected by sputum mucus are more resistant. Thus, tuberculosis bacteria in sputum can withstand drying for up to 90 days. Some capsule- and mucus-forming bacteria are resistant to desiccation. But bacterial spores are particularly resistant.

Drying under vacuum from a frozen state - lyophilization - is used to prolong the viability and preservation of microorganisms. Lyophilized cultures of microorganisms and immunobiological preparations are stored for a long time (for several years) without changing their original properties.

Effect of radiation. Non-ionizing radiation - ultraviolet and infrared rays sunlight, as well as ionizing radiation - gamma radiation from radioactive substances and high-energy electrons have a detrimental effect on microorganisms after a short period of time. UV rays are used to disinfect air and various objects in hospitals, maternity hospitals, and microbiological laboratories. For this purpose, bactericidal UV lamps with a wavelength of 200-450 nm are used.

Ionizing radiation is used to sterilize disposable plastic microbiological glassware, culture media, dressings, medicines etc. However, there are bacteria that are resistant to ionizing radiation, for example Micrococcus radiodurans was isolated from a nuclear reactor.

Action of chemicals. Chemical substances can have different effects on microorganisms: serve as sources of nutrition; not to exert any influence; stimulate or suppress growth. Chemicals that destroy microorganisms in the environment are called disinfectants. The process of destroying microorganisms in the environment is called disinfection. Antimicrobial chemicals can have bactericidal, virucidal, fungicidal effects, etc.

Chemical substances used for disinfection belong to various groups, among which the most widely represented are substances related to chlorine-, iodine- and bromine-containing compounds and oxidizing agents. In chlorine-containing preparations, chlorine has a bactericidal effect. These drugs include bleach, chloramines, pantocid, neopantocid, sodium hypochlorite, calcium hypochlorite, desam, chlordesine, sulfochloranthine, etc. Iodopyrine and dibromantine are considered promising antimicrobial drugs based on iodine and bromine. Intense oxidizing agents are hydrogen peroxide, potassium permanganate, etc. They have a pronounced bactericidal effect.

Phenols and their derivatives include phenol, lysol, lysoid, creosote, creolin, chlor-p-naphthol and hexachlorophene.

Bactericidal soaps are also produced: phenol, tar, green medical, “Hygiene”. Soap "Hygiene" contains 3-5% hexachlorophene, has the best bactericidal properties and is recommended for washing the hands of employees of infectious diseases hospitals, maternity hospitals, child care institutions, and enterprises Catering and microbiological laboratories.

Acids and their salts (oxolinic, salicylic, boric) also have an antimicrobial effect; alkalis (ammonia and its salts, borax); alcohols (70-80° ethanol, etc.); aldehydes (formaldehyde, p-propiolactone).

A promising group of disinfectants are surfactants related to quaternary compounds and ampholytes, which have bactericidal, detergent properties and low toxicity (nirtan, ampholan, etc.).

For disinfection of precision instruments (e.g. spaceships), as well as equipment and apparatus, use a gas mixture of ethylene oxide and methyl bromide. Disinfection is carried out under sealed conditions.

Influence of biological factors. Microorganisms are in various relationships with each other. The coexistence of two different organisms is called symbiosis (from the Greek simbiosis - life together). There are several options for beneficial relationships: metabiosis, mutualism, commensalism, satelliteism.

Metabiosis is a relationship between microorganisms in which one microorganism uses the waste products of another organism for its vital functions. Metabiosis is characteristic of soil nitrifying bacteria, which use ammonia for metabolism - a waste product of ammonifying soil bacteria.

Mutualism is a mutually beneficial relationship between different organisms. An example of a mutualistic symbiosis is lichens - a symbiosis of a fungus and blue-green algae. Receiving organic substances from algae cells, the fungus, in turn, supplies them with mineral salts and protects them from drying out.

Commensalism (from Latin commensalis - table mate) - cohabitation of individuals different types, in which one species benefits from symbiosis without causing harm to the other. Commensals are bacteria, representatives of the normal human microflora.

Satellism is an increase in the growth of one type of microorganism under the influence of another microorganism. For example, colonies of yeast or sarcin, releasing metabolites into the nutrient medium, stimulate the growth of colonies of microorganisms around them. With the joint growth of several types of microorganisms, their physiological functions and properties can be activated, which leads to a more rapid effect on the substrate.

Antagonistic relationships, or antagonistic symbiosis, are expressed in the form of an adverse effect of one type of microorganism on another, leading to damage and even death of the latter. Antagonist microorganisms are common in soil, water and the body of humans and animals. The antagonistic activity of representatives of the normal microflora of the human large intestine - bifidobacteria, lactobacilli, E. coli, etc., which are antagonists of putrefactive microflora, is well known.

The mechanism of antagonistic relationships is varied. A common form of antagonism is the formation of antibiotics - specific metabolic products of microorganisms that suppress the development of microorganisms of other species. There are other manifestations of antagonism, for example, a high reproduction rate, the production of bacteriocins, in particular colicins, the production of organic acids and other products that change the pH of the environment.

4.7. Microflora of plant medicinal raw materials, phytopathogenic microorganisms, microbiological control of medicines

Herbal medicinal raw materials can become contaminated with microorganisms during the process of their production: infection occurs through water, non-sterile pharmaceutical containers, the air of production premises and the hands of personnel. Contamination also occurs due to the normal microflora of plants and phytopathogenic microorganisms - pathogens of plant diseases. Phytopathogenic microorganisms are capable of spreading and infecting large numbers of plants.

Microorganisms that normally develop on the surface of plants are classified as epiphytes (Greek epi - above, phyton - plant). They do not cause harm, are antagonists of some phytopathogenic microorganisms, and grow due to normal plant secretions and organic contamination of the plant surface. Epiphytic microflora prevents the penetration of phytopathogenic microorganisms into plant tissue, thereby strengthening plant immunity. Nai large quantity The epiphytic microflora consists of gram-negative bacteria Erwinia herbicola, which form golden-yellow colonies on meat peptone agar. These bacteria are antagonists of the causative agent of soft rot of vegetables. Other bacteria are also found normally - Pseudomonas fluorescens, less commonly Bacillus mesentericus and a small amount of fungi. Microorganisms are found not only on leaves, stems, but also on plant seeds. Violation of the surface of plants and their seeds contributes to the accumulation of large amounts of dust and microorganisms on them. The composition of plant microflora depends on the species, age of plants, soil type and temperature environment. When humidity increases, the number of epiphytic microorganisms increases, and when humidity decreases, it decreases.

In the soil, near the roots of plants, there is a significant amount of

Microorganisms are found in the most unsuitable, in our opinion, ecological niches. Thus, some species of bacteria (Bacillus submarinus) are able to live in the oceans at a depth of more than 5000 m, withstanding hydrostatic pressure over 3.1–10 8 Pa, the extremely thermophilic bacteria Thermus aquaticus are isolated from the water and silt of hot springs, the temperature of which reaches 92 ° C , extreme halophilic bacteria found in Dead Sea water.

Certain environmental factors can have different effects on microorganisms, have a depressing effect on them, or cause the death of the microbial population. The positive or negative effect of the active factor is determined both by the nature of the factor itself and by the properties of the microorganism.

Humidity. The presence of moisture determines the level of metabolic processes in the cell, the flow of nutrient substrate substances into it, the energy of growth and reproduction of bacteria.

Most bacteria develop normally at environmental humidity above 20%.

Drying of bacteria leads to dehydration of the cell cytoplasm, almost complete cessation of metabolic processes and ultimately to the transition of the microbial cell to a state of suspended animation. Drying is used in food storage.

Often, even in conditions of deep drying, bacteria remain viable. Thus, Mycobacterium tuberculosis remains viable in the dried sputum of a patient for more than 10 months, spores of bacilli anthrax in a dry state they survive up to 10 years. Method sublimation (drying) Currently, it is widely used for long-term storage of live vaccines against tuberculosis, plague, smallpox, influenza, as well as for maintaining industrial and museum cultures of microorganisms.

Temperature. The life activity of prokaryotes directly depends on the temperature range. It is characterized by three cardinal points: the minimum temperature below which the growth and development of bacteria stops; the optimal temperature corresponding to the highest growth rate of a microbe, the maximum temperature above which the growth rate of bacteria practically decreases to zero. Based on their temperature range, all prokaryotes are divided into 3 groups: psychrophiles, mesophiles and thermophiles.

Psychrophiles(from the Greek psychros - cold, phileo - love) are represented by bacteria that develop at low temperatures from – 5 to 20–35 0 C. Among them, a subgroup of obligate psychrophiles is distinguished, unable to grow at temperatures above 20 ° C. These are bacteria from deep lakes, northern seas and oceans. The second very large subgroup consists of facultative psychrophiles - bacteria that have adapted to the action of variable temperatures from – 5 ° C to 20–35 ° C and inhabit the temperate climate zone.

Low temperatures slow down metabolic processes in cells, which is the basis for the use of refrigerators, cellars and glaciers for storing food. Many microorganisms in the thickness natural ice capable of remaining in a state of suspended animation “buried” for up to 12,000 years.

TO mesophiles(from the Greek mesos - average) refers to the overwhelming mass of prokaryotes, for which the temperature range lies within 10–47 ° C, with optimal temperatures of 30–40 ° C. This group includes many pathogenic bacteria that cause diseases in warm-blooded animals and humans.

Thermophiles(from the Greek thermos - heat, heat) constitute a diverse group of bacteria growing in the temperature range from 10 to 55–60° C. Facultative thermophiles develop equally successfully at temperatures of 55–60° C and at 10–20° C, and obligate thermophiles, incapable of growth at temperatures below 40° C. Extreme thermophiles live at temperatures above 70° C. They were isolated from hot springs and assigned to the genera Thermomicrobium, Thermus, Thermothrix, etc. They exhibit particular resistance to high temperatures bacterial spores that can withstand boiling temperatures for two to three hours.

Radiant Energy. Different kinds radiation affects bacteria differently. Infrared radiation (wavelengths from 760 nm to 400 μm) is not capable of causing any significant photochemical changes in living cells. X-rays (wavelengths less than 10 nm) ionize macromolecules of living cells. The resulting photochemical changes cause the development of mutations or cell death. Selected species bacteria are remarkably resistant to x-rays. These are thionic bacteria that live in uranium ore deposits, as well as Micrococcus radiodurans bacteria, isolated from the water of nuclear reactors at a dose of ionizing radiation of 2–3 million rads.

Visible light (wavelengths from 380 to 760 nm) has a beneficial effect only on the development of photosynthetic bacteria.

Strong effect have ultraviolet rays with a wavelength of 253.7 nm. The bactericidal effect of ultraviolet rays on bacteria is based on their use for the disinfection of food, culture media, dishes, as well as the disinfection of wards, operating rooms, and maternity hospital premises.

Ultrasound. Ultrasound is high-frequency vibrations of sound waves (more than 20,000 Hz). Ultrasound has a powerful bactericidal effect on prokaryotes. The strength of this action depends on the frequency of vibrations, the duration of exposure, as well as on the physiological state and individual characteristics of the microorganism. With prolonged sonication of a microbial culture, a 100% lethal effect is observed.

The effect of ultrasound is irreversible physical and chemical changes in the components of the microbial cell and mechanical damage to all cellular structures. Currently, ultrasound is used to sterilize food, laboratory equipment and vaccines.

Environmental reaction. The reaction of the environment is one of the important factors determining the development of bacteria, affecting the solubility of nutrient substrate substances and their entry into the cell. A change in the reaction of the environment is often accompanied by an increase in the concentration of toxic compounds.

Prokaryotes can be divided into several groups in relation to the acidity of the environment. The vast majority of them belong to neutrophils, for which a neutral environment is optimal. In this group, many bacteria are capable of exhibiting acid or alkali resistance.

Among prokaryotes there are acidophiles, developing in acidic environment with a pH value of 2–3. Moderate acidophiles include bacteria that live in the water of acidic swamps and lakes, as well as in acidic soils with
pH 3–4. Extreme acidophiles are bacteria of the genera Thiobacillus and Sulfomonas, as well as Thermoplasma acidophila.

Alkalophilic bacteria exist in alkaline environment. Alkaliphilic bacteria include representatives of the genus Bacillus and Vibrio cholerae, the reproduction of which increases at a pH value above 9.

The use of marinades is based on the negative effect of increased acidity on most microorganisms.

Oxygen. Most prokaryotes require oxygen to survive and are called obligate (strict) aerobes.

Obligate aerobes are able to withstand oxygen concentrations of about 40–50%. Bacteria for which molecular oxygen is required in small quantities - no more than 2% - are called microaerophiles.

The second group of prokaryotes consists of microorganisms for whose life activity molecular oxygen is not needed. Such microorganisms are called obligate anaerobes. These include butyric acid, methane-forming, sulfate-reducing and some other bacteria. In the cells of obligate anaerobes, oxidation of substrate substances occurs without the participation of oxygen. These include representatives of the genera Methanobacterium, Methanosarcina, Fusobacterium, etc.

Many types of butyric acid bacteria are resistant to molecular oxygen and are called aerotolerant. An example of aerotolerants are bacteria of the genus Clostridium. Endospores of butyric acid bacteria exhibit particular aerotolerance. Prokaryotes, capable of growing in both aerobic and anaerobic conditions and switching their energy metabolism from one method of obtaining energy to another, are called facultative aerobes or facultative anaerobes. Examples of facultative anaerobes are denitrifying and desulphating bacteria, as well as a large group of enterobacteria.

Antiseptics. Chemical compounds that have a detrimental effect on microorganisms are called antiseptics.

The effect of an antiseptic on bacteria can be bacteriostatic or bactericidal. The bacteriostatic effect only stops the growth and reproduction of microbial cells; bactericidal - causes the death of bacteria, which is often accompanied by cell lysis. The resulting effect depends on the nature itself chemical compounds, their concentration, on the duration of action of the antiseptic on microorganisms, as well as on associated environmental factors - temperature, pH value, etc.

Antiseptics are represented by various organic and inorganic compounds. From Not organic compounds strong antiseptics are salts of heavy metals - mercury (sublimate), lead, silver, zinc, etc. Salts of mercury, silver, arsenic exhibit a strong inhibitory effect on the enzymes of microbial cells. Even in small concentrations of 1:1000, heavy metal salts cause the death of most bacteria within a few minutes.

Of the organic compounds, ethyl and isopropyl alcohols (70% solutions), phenol, cresol and their derivatives, and formaldehyde have an antiseptic effect. Phenol (carbolic acid) is especially widely used. Most microbes die from the action of a 1–5% solution of carbolic acid. Formaldehyde is a strong antiseptic.

Temperature - one of the main factors determining the possibility and intensity of microorganism reproduction.

Microorganisms can grow and exhibit their vital activity in a certain temperature range and depending on the relationship to temperature are divided into psychrophiles, mesophiles and thermophiles. Temperature ranges for the growth and development of microorganisms of these groups are given in Table 9.1.

Table 9.1 Division of microorganisms into groups depending on

from relation to temperature

microorganisms		T(°C) max.		Separate representatives
1. Psychrophiles (cold-loving)				Bacteria living in refrigerators, marine bacteria
2. Mesophiles				Most fungi, yeasts, bacteria
3. Thermophiles (heat-loving)				Bacteria living in hot springs. Most form persistent spores

The division of microorganisms into 3 groups is very arbitrary, since microorganisms can adapt to temperatures that are unusual for them.

Temperature limits for growth are determined by the thermoresistance of enzymes and cellular structures containing proteins.

Among mesophiles, there are forms with a high temperature maximum and a low minimum. Such microorganisms are called thermotolerant.

The effect of high temperatures on microorganisms. Increasing the temperature above the maximum can lead to cell death. The death of microorganisms does not occur instantly, but over time. With a slight increase in temperature above the maximum, microorganisms may experience"heat shock"

and after a short stay in this state they can be reactivated. The mechanism of the destructive effect of high temperatures is associated with the denaturation of cellular proteins.

The denaturation temperature of proteins is affected by their water content (the less water in the protein, the higher the denaturation temperature). Young vegetative cells, rich in free water, die when heated faster than old, dehydrated ones. Heat resistance –

the ability of microorganisms to withstand prolonged heating at temperatures exceeding the temperature maximum of their development. The death of microorganisms occurs when different meanings

temperatures and depends on the type of microorganism. Thus, when heated in a humid environment for 15 minutes at a temperature of 50–60 °C, most fungi and yeasts die; at 60–70 °C – vegetative cells of most bacteria, fungal and yeast spores are destroyed at 65–80 °C. The vegetative cells of thermophiles (90–100 °C) and bacterial spores (120 °C) have the greatest heat resistance.

The high heat resistance of thermophiles is due to the fact that, firstly, the proteins and enzymes of their cells are more resistant to temperature, and secondly, they contain less moisture. In addition, the rate of synthesis of various cellular structures in thermophiles is higher than the rate of their destruction.

The heat resistance of bacterial spores is associated with their low content of free moisture and multilayer shell, which includes calcium salt-dipicolinic acid. Various methods of destroying microorganisms in food products are based on the destructive effect of high temperatures. These include boiling, cooking, blanching, frying, as well as sterilization and pasteurization. Pasteurization – the process of heating to 100˚C during which the vegetative cells of microorganisms are destroyed. Sterilization –

complete destruction of vegetative cells and microorganism spores. The sterilization process is carried out at temperatures above 100 °C. Microorganisms are more resistant to low temperatures than to high temperatures. Despite the fact that the reproduction and biochemical activity of microorganisms stop at temperatures below the minimum, cell death does not occur, because microorganisms become (suspended animation hidden life

) and remain viable for a long time. As the temperature rises, cells begin to multiply intensively. Reasons death of microorganisms when exposed to low temperatures

are:

Metabolic disease;

An increase in the osmotic pressure of the environment due to freezing of water;

Ice crystals may form in the cells, destroying the cell wall.

Low temperature is used when storing food in a refrigerated state (at a temperature of 10 to –2 °C) or frozen (from –12 to –30 °C). Radiant energy. In nature, microorganisms are constantly exposed to solar radiation

. Light is necessary for the life of phototrophs. Chemotrophs can grow in the dark, and with prolonged exposure to solar radiation, these microorganisms can die. The effect of radiant energy is subject to laws of photochemistry: changes in cells can only be caused by absorbed rays.

Consequently, the penetrating ability of the rays, which depends on the wavelength and dose, is important for the effectiveness of irradiation.

The radiation dose, in turn, is determined by the intensity and time of exposure. In addition, the effect of radiant energy depends on the type of microorganism, the nature of the irradiated substrate, the degree of its contamination with microorganisms, as well as on temperature.

Low intensities of visible light (350–750 nm) and ultraviolet rays (150–300 nm), as well as low doses of ionizing radiation either do not affect the vital activity of microorganisms or lead to an acceleration of their growth and stimulation of metabolic processes, which is associated with the absorption of light quanta certain components or substances of cells and their transition to an electronically excited state. Higher doses of radiation cause inhibition of certain metabolic processes, and the action of ultraviolet and x-rays can lead to changes in the hereditary properties of microorganisms - mutations

which is widely used to obtain highly productive strains. Death of microorganisms under the influence of ultraviolet rays

linked:

With inactivation of cellular enzymes;

With the destruction of nucleic acids;

It should be noted that the most resistant to ultraviolet rays are bacterial spores, then fungal and yeast spores, then colored (pigmented) bacterial cells. The least resistant are vegetative bacterial cells.

Death of microorganisms under the influence of ionizing radiation called:

Radiolysis of water in cells and substrate. In this case, free radicals, atomic hydrogen, peroxides, which, when interacting with other substances of the cell, cause a large number of reactions that are not characteristic of a normally living cell;

Inactivation of enzymes, destruction of membrane structures, nuclear apparatus.

The radiostability of various microorganisms varies widely, and microorganisms are much more radioresistant than higher organisms (hundreds and thousands of times). The most resistant to ionizing radiation are bacterial spores, then fungi and yeast, and then bacteria.

The destructive effect of ultraviolet and x-ray γ-rays is used in practice.

Ultraviolet rays are used to disinfect the air of refrigeration chambers, medical and industrial premises, and the bactericidal properties of ultraviolet rays are used to disinfect water.

Processing food products with low doses of gamma radiation is called radurization.

Electromagnetic vibrations and ultrasound. Radio waves- This electromagnetic waves, characterized by a relatively long length (from millimeters to kilometers) and frequencies from 3·10 4 to 3·10 11 hertz.

The passage of short and ultra-radio waves through a medium causes the appearance of high-frequency (HF) and ultra-high-frequency (microwave) alternating currents in it. In an electromagnetic field Electric Energy converted to heat.

The death of microorganisms in a high-intensity electromagnetic field occurs as a result of the thermal effect, but the mechanism of action of microwave energy on microorganisms has not been fully disclosed.

IN last years UHF electromagnetic processing of food products is increasingly used in the food industry (for cooking, drying, baking, reheating, defrosting, pasteurization and sterilization of food products). Compared to the traditional method of heat treatment, the time of heating with microwave energy to the same temperature is reduced many times, and therefore the taste and nutritional properties of the product are more fully preserved.

Ultrasound. Ultrasound refers to mechanical vibrations with frequencies greater than 20,000 vibrations per second (20 kHz).

The nature of the destructive effect of ultrasound on microorganisms is associated with:

WITH cavitation effect. When ultrasonic waves propagate in a liquid, rapidly alternating rarefaction and compression of liquid particles occurs. When the medium is discharged, tiny hollow spaces are formed - “bubbles”, which are filled with environmental vapors and gases. During compression, at the moment the cavitation “bubbles” collapse, a powerful hydraulic shock wave arises, causing a destructive effect;

With electrochemical action of ultrasonic energy. In an aquatic environment, water molecules are ionized and oxygen dissolved in it is activated. In this case, highly reactive substances are formed, which cause a number of chemical processes that adversely affect living organisms.

Due to its specific properties, ultrasound is increasingly used in various fields of engineering and technology in many industries. National economy. Research is underway on the use of ultrasound energy for sterilization drinking water, food products (milk, fruit juices, wines), washing and sterilization of glass containers.

Physical, chemical and biological environmental factors have different effects on microorganisms: bactericidal - leading to cell death; bacteriostatic - suppressing the proliferation of microorganisms; mutagenic - changing the hereditary properties of microbes.

4.3.1. Influence physical factors

Effect of temperature. Representatives of various groups of microorganisms develop at certain temperature ranges. Bacteria,

those growing at low temperatures are called psychrophiles; at average (about 37 °C) - mesophytes; at high temperatures - thermophiles.

Psychrophilic microorganisms grow at temperatures from -10 to 40 "C; the temperature optimum ranges from 15 to 40 ° C, approaching the temperature optimum of mesophilic bacteria. Psychrophiles include a large group of saprophytes - inhabitants of the soil, seas, fresh water bodies and Wastewater(iron bacteria, pseudomonads, luminous bacteria, bacilli). Some psychrophiles can cause food spoilage in the cold. Some pathogenic bacteria also have the ability to grow at low temperatures (the causative agent of pseudotuberculosis reproduces at a temperature of 4 °C, and the causative agent of plague - in the range from 0 to 40 °C with an optimum growth of 25 °C). Depending on the cultivation temperature, the properties of bacteria change. So , Serratia marcescens forms at a temperature of 20-25 ° C a greater amount of red pigment (prodigiosan) than at a temperature of 37 ° C. The plague pathogen grown at 25 °C is more virulent than at 37 °C. The synthesis of polysaccharides, including capsular ones, is activated at lower cultivation temperatures.

Mesophiles grow in the temperature range from 10 to 47 ° C, the optimum growth is about 37 ° C. They include the main group of pathogenic and opportunistic bacteria.

Thermophilic bacteria develop at higher temperatures (from 40 to 90 °C). At the bottom of the ocean in hot sulfide waters live bacteria that develop at a temperature of 250-300 ° C and a pressure of 265 atm. Thermophiles live in hot springs and participate in the processes of self-heating of manure, grain, and hay. The presence of a large number of thermophiles in the soil indicates its contamination with manure and compost. Since manure is the richest in thermophiles, they are considered an indicator of soil contamination.

The temperature factor is taken into account when carrying out sterilization. Vegetative forms of bacteria die at a temperature of 60 °C for 20-30 minutes, spores die in an autoclave at 120 °C under pressure steam conditions.

Microorganisms tolerate low temperatures well. Therefore they can

Store frozen for a long time, including at liquid nitrogen temperature (-173 °C).

Drying. Dehydration causes dysfunction of most microorganisms. The most sensitive to drying are the pathogens of gonorrhea, meningitis, cholera, typhoid fever, dysentery and other pathogenic microorganisms. Microorganisms protected by sputum mucus are more resistant. Thus, tuberculosis bacteria in sputum can withstand drying for up to 90 days. Some capsulo- and mucus-forming bacteria are resistant to desiccation. Bacterial spores are particularly resistant. For example, anthrax spores can persist in the soil for centuries.

To prolong the viability, when preserving microorganisms, lyophilization is used - drying under vacuum from a frozen state. Lyophilized cultures of microorganisms and immunobiological preparations are stored for a long time (for several years) without changing their original properties.

Effect of radiation. Ionizing radiation is used to sterilize disposable plastic microbiological glassware, culture media, dressings, medications, etc. However, there are bacteria that are resistant to ionizing radiation, for example Micrococcus radiodurans was isolated from a nuclear reactor.

Non-ionizing radiation - ultraviolet and infrared rays of sunlight, as well as ionizing radiation - gamma radiation from radioactive substances and high-energy electrons have a detrimental effect on microorganisms within a short period of time.

Ultraviolet rays reaching the earth's surface have a wavelength of 290 nm. UV rays are used to disinfect air and various objects in hospitals, maternity hospitals, and microbiological laboratories. For this purpose, bactericidal ultraviolet lamps with a wavelength of 200-400 nm are used.

4.3.2. Effect of chemicals

Chemicals can have different effects on microorganisms: serve as sources of nutrition; not to exert any influence; stimulate or suppress growth, cause death. Antimicrobial chemicals are used as antiseptics and disinfectants, as they have bactericidal, virucidal, fungicidal, etc. effects.

Chemicals used for disinfection belong to various groups, among which the most widely represented are chlorine-, iodine-, and bromine-containing compounds and oxidizing agents (see Section 7.7).

4.3.3. Influence of biological factors
Microorganisms are in different
significant relationships with each other.
Coexistence of two different
organisms are called symbiosis(from Greek
symbiosis- living together). Distinguish
several options that are useful in relation to each other
ideas: metabiosis, mutualism, commensalism,
satelliteism.

Metabiosis- the relationship of microorganisms in which one of them uses the waste products of the other for its vital activity. Metabiosis is characteristic of soil nitrifying bacteria, which use ammonia for their metabolism, a waste product of ammonifying soil bacteria.

Mutualism- mutually beneficial relationships between different organisms. An example of a mutualistic symbiosis is lichens - a symbiosis of a fungus and blue-green algae. Receiving organic substances from algae cells, the fungus, in turn, supplies them with mineral salts and protects them from drying out.

Commensalism(from lat. commensalis- companion) - cohabitation of individuals of different species, in which one species benefits from the symbiosis without causing harm to the other. Commensals are bacteria - representatives of the normal human microflora

Satellism- increased growth of one type of microorganism under the influence of another type of microorganism. For example, colonies of yeast or sarcin, releasing metabolites into the nutrient medium, stimulate the growth of colonies of other microorganisms around them. With the joint growth of several types of microorganisms, their physiological functions and properties can be activated, which leads to a more rapid effect on the substrate.

Antagonistic relationships, or antagonistic symbiosis, are expressed in the form of an adverse effect of one type of microorganism on another, leading to damage and even death of the latter. Antagonist microorganisms are common in soil, water and in the body of humans and animals. The antagonistic activity against foreign and putrefactive microflora of representatives of the normal microflora of the human large intestine - bifidobacteria, lactobacilli, E. coli, etc. - is well known.

The mechanism of antagonistic relationships is varied. A common form of antagonism is the formation of antibiotics - specific metabolic products of microorganisms that suppress the development of microorganisms of other species. There are other manifestations of antagonism, for example, a high rate of reproduction, production bacteriocins, in particular colicins, production of organic acids and other products that change the pH of the environment.