The cause of death of microorganisms under the influence of ionizing radiation. The influence of physical and chemical factors on microorganisms
Influence of physical factors.
The effect of temperature. Different groups of microorganisms develop at certain temperature ranges. Bacteria growing at low temperatures are called psychrophiles, at medium (about 37 ° C) - mesophiles, at high - thermophiles.
To psychrophilic microorganisms includes a large group of saprophytes - inhabitants of the soil, seas, fresh water and Wastewater(iron bacteria, pseudomonads, luminous bacteria, bacilli). Some of them can cause food spoilage in the cold. Some pathogenic bacteria also have the ability to grow at low temperatures (the causative agent of pseudotuberculosis multiplies at a temperature of 4 °C). Depending on the cultivation temperature, the properties of bacteria change. The temperature range at which the growth of psychrophilic bacteria is possible ranges from -10 to 40 °C, and the temperature optimum - 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 of 10-47 °C; the optimum growth for most of them is 37 °C.
At higher temperatures (from 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, participate in the processes of self-heating of manure, grain, 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 as an indicator of soil contamination.
Microorganisms withstand low temperatures well. Therefore, they can be stored frozen for a long time, including at liquid gas temperature (-173 °C).
Drying. Dehydration causes disruption of the functions 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.
Drying under vacuum from a frozen state - lyophilization - is used to prolong the viability, 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 of 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, microbiological laboratories. For this purpose, bactericidal lamps of UV radiation with a wavelength of 200-450 nm are used.
Ionizing radiation is used to sterilize disposable plastic microbiological utensils, nutrient media, dressings, drugs, etc. However, there are bacteria that are resistant to ionizing radiation, for example, Micrococcus radiodurans was isolated from a nuclear reactor.
Sterilization involves the complete inactivation of microbes in the objects being processed.
There are three main methods of sterilization: thermal, radiation, chemical.
Heat sterilization based on the sensitivity of microbes to high temperature. At 60 "C and the presence of water, protein denaturation, degradation of nucleic acids, lipids occurs, as a result of which the vegetative forms of microbes die. Spores containing a very large amount of water in bound state and having dense shells, are inactivated at 160-170 °C.
For heat sterilization, mainly dry heat and pressurized steam are used.
dry heat sterilization carried out in air sterilizers (the former name is “dry ovens or Pasteur ovens”). The air sterilizer is a tightly closed metal cabinet heated by electricity and equipped with a thermometer. Disinfection of the material in it is carried out, as a rule, at 160 °C for 120 minutes. However, other modes are also possible: 200 ° C - 30 minutes, 180 "C - 40 minutes.
Dry heat sterilize laboratory glassware and other glassware, tools, silicone rubber, i.e. objects that do not lose their qualities at high temperatures.
Most sterilized items do not withstand such treatment, and therefore they are decontaminated in steam sterilizers.
Processing with steam under pressure in steam sterilizers (the old name - "autoclaves") is the most versatile method of sterilization.
Steam sterilizer (there are many of its modifications) - a metal cylinder with strong walls, hermetically sealed, consisting of a water-steam and sterilizing chambers. The apparatus is equipped with a pressure gauge, thermometer and other instrumentation. An increased pressure is created in the autoclave, which leads to an increase in the boiling point.
Since, in addition to high temperature, steam also affects microbes, spores die already at 120 ° C. The most common operating mode of a steam sterilizer: 2 atm - 121 ° C - 15-20 min. Sterilization time decreases with increasing atmospheric pressure and, consequently, the boiling point (136 ° C - 5 min). Microbes die in a few seconds, but the material is processed for a longer time, because, firstly, the high temperature must also be inside the sterilized material and, secondly, there is a so-called safety margin (calculated for a small malfunction of the autoclave).
Most of the items are sterilized in an autoclave: dressings, underwear, corrosion-resistant metal instruments, nutrient media, solutions, infectious material, etc.
One type of heat sterilization is fractional sterilization, which is used to process materials that cannot withstand temperatures above 100 ° C, for example, to sterilize nutrient media with carbohydrates, gelatin. They are heated in a water bath at 80°C for 30-60 minutes.
Currently, another method of heat sterilization is used, designed specifically for milk - ultra-high temperature(UHT): milk is processed for a few seconds at 130-150 °C.
Chemical sterilization involves the use of toxic gases: ethylene oxide, a mixture of OB (a mixture of ethylene oxide and methyl bromide in a weight ratio of 1:2.5) and formaldehyde. These substances are alkylating agents, their ability to inactivate active groups in enzymes, other proteins, DNA and RNA in the presence of water leads to the death of microorganisms.
Sterilization with gases is carried out in the presence of steam at a temperature of 18 to 80 ° C in special chambers. In hospitals, formaldehyde is used, in industrial conditions - ethylene oxide and a mixture of OB.
Before chemical sterilization, all products to be processed must be dried.
This type of sterilization is unsafe for personnel, for the environment and for patients using the sterilized items (most sterilizing agents remain on the items).
However, there are objects that can be damaged by heat, such as optical instruments, radio and electronic equipment, objects made of non-heat-resistant polymers, protein culture media, etc., for which only chemical sterilization is suitable. For example, spacecraft and satellites, equipped with precision equipment, are decontaminated with a gas mixture (ethylene oxide and methyl bromide) to decontaminate them.
AT recent times due to the widespread use in medical practice of products made of thermolabile materials equipped with optical devices, such as endoscopes, they began to use decontamination with chemical solutions. After cleaning and disinfection, the device is placed on certain time(from 45 to 60 min) in a sterilizing solution, then the device must be washed with sterile water. For sterilization and washing use sterile containers with lids. The product sterilized and washed from the sterilizing solution is dried with sterile wipes and placed in a sterile container. All manipulations are carried out under aseptic conditions and in sterile gloves. Store these products for no more than 3 days.
Radiation sterilization is carried out either with the help of gamma radiation, or with the help of accelerated electrons.
Radiation sterilization is an alternative to gas sterilization in industrial environments and is also used in cases where the objects to be sterilized cannot withstand high temperatures. Radiation sterilization allows you to process a large number of items at once (for example, disposable syringes, blood transfusion systems). Due to the possibility of large-scale sterilization, the use of this method is quite justified, despite its environmental hazard and uneconomical.
Another method of sterilization is filtration.. Filtration using various filters (ceramic, asbestos, glass), and especially membrane ultrafilters from colloidal solutions of nitrocellulose or other substances, allows you to free liquids (blood serum, drugs) from bacteria, fungi, protozoa and even viruses. To speed up the filtration process, it is common to create an increased pressure in the container with the filtered liquid or a reduced pressure in the container with the filtrate.
Currently are increasingly being used modern methods sterilization, created on the basis of new technologies, using plasma, ozone.
Influence of physical factors .
The effect of temperature. Different groups of microorganisms develop at certain temperature ranges. Bacteria growing at low temperatures are called psychrophiles, at medium (about 37 ° C) - mesophiles, at high - thermophiles.
To psychrophilic microorganisms applies large group saprophytes - inhabitants of the soil, seas, fresh water and wastewater (iron bacteria, pseudomonads, luminous bacteria, bacilli). Some of them can cause food spoilage in the cold. Some pathogenic bacteria also have the ability to grow at low temperatures (the causative agent of pseudotuberculosis multiplies at a temperature of 4 °C). Depending on the cultivation temperature, the properties of bacteria change. The temperature range at which the growth of psychrophilic bacteria is possible ranges from -10 to 40 °C, and the temperature optimum - 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 of 10-47 °C; the optimum growth for most of them is 37 °C.
At higher temperatures (from 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, participate in the processes of self-heating of manure, grain, 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 as an indicator of soil contamination.
Microorganisms withstand low temperatures well. Therefore, they can be stored frozen for a long time, including at liquid gas temperature (-173 °C).
Drying. Dehydration causes disruption of the functions 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.
Drying under vacuum from a frozen state - lyophilization - is used to prolong the viability, 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 of sunlight, as well as ionizing radiation - gamma radiation of 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, microbiological laboratories. For this purpose, bactericidal lamps of UV radiation with a wavelength of 200-450 nm are used.
Ionizing radiation is used to sterilize disposable plastic microbiological utensils, nutrient media, dressings, drugs, etc. However, there are bacteria that are resistant to ionizing radiation, for example, Micrococcus radiodurans was isolated from a nuclear reactor.
Action of chemicals . Chemicals can have different effects on microorganisms: serve as food sources; not exert any influence; stimulate or inhibit growth. Chemical substances that destroy microorganisms in the environment are called disinfectants. Antimicrobial chemicals can be bactericidal, virucidal, fungicidal, etc.
Chemicals 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.
Acids and their salts (oxolinic, salicylic, boric) also have an antimicrobial effect; alkalis (ammonia and its salts).
Sterilization- involves the complete inactivation of microbes in objects that have undergone processing.
Disinfection- a procedure involving the treatment of an object contaminated with microbes in order to destroy them to such an extent that they cannot cause infection when using this object. As a rule, disinfection kills most of the microbes (including all pathogens), but spores and some resistant viruses may remain in a viable state.
Asepsis- a set of measures aimed at preventing the infection pathogen from entering the wound, the patient's organs during operations, medical and diagnostic procedures. Asepsis methods are used to combat exogenous infection, the sources of which are patients and bacteria carriers.
Antiseptics- a set of measures aimed at the destruction of microbes in a wound, pathological focus or the body as a whole, to prevent or eliminate the inflammatory process.
Dysbiosis. Preparations for the restoration of the microbiota.Stateeubiosis - dynamic balance of normal microflora and the human body - can be disturbed under the influence of environmental factors, stress, widespread and uncontrolled use of antimicrobials, radiation therapy and chemotherapy, poor nutrition, surgical interventions, etc. As a result, colonization resistance is violated. Abnormally multiplied transient microorganisms produce toxic metabolic products - indole, skatole, ammonia, hydrogen sulfide.
Conditions that develop as a result of the loss of normal functions of the microflora are calleddysbacteriosis anddysbiosis .
With dysbacteriosis there are persistent quantitative and qualitative changes in the bacteria that make up the normal microflora. With dysbiosis, changes also occur among other groups of microorganisms (viruses, fungi, etc.). Dysbiosis and dysbacteriosis can lead to endogenous infections.
Dysbioses are classified by etiology (fungal, staphylococcal, proteic, etc.) and by localization (dysbiosis of the mouth, intestines, vagina, etc.). Changes in the composition and functions of the normal microflora are accompanied by various disorders: the development of infections, diarrhea, constipation, malabsorption syndrome, gastritis, colitis, peptic ulcer disease, malignant neoplasms, allergies, urolithiasis, hypo- and hypercholesterolemia, hypo- and hypertension, caries, arthritis, liver damage, etc.
Violations of the normal human microflora are defined as follows:
1. Identification of the species and quantitative composition of representatives of the microbiocenosis of a certain biotope (intestine, mouth, vagina, skin, etc.) - by seeding from dilutions of the material under study or by imprints, flushing onto appropriate nutrient media (Blaurock medium - for bifidobacteria; MPC-2 medium - for lactobacilli; anaerobic blood agar - for bacteroids; Levin's or Endo's medium - for enterobacteria; bile-blood agar - for enterococci; blood agar - for streptococci and hemophils; meat peptone agar with furagin - for Pseudomonas aeruginosa, Sabouraud's medium - for fungi and etc.).
2. Determination in the test material of microbial metabolites - markers of dysbiosis (fatty acids, hydroxy fatty acids, fatty acid aldehydes, enzymes, etc.). For example, the detection of beta-aspartylglycine and beta-aspartylysin in the faeces indicates a violation of the intestinal microbiocenosis, since these dipeptides are normally metabolized by the intestinal anaerobic microflora.
To restore normal microflora: a) carry out selective decontamination; b) prescribe preparations of probiotics (eubiotics), obtained from freeze-dried living bacteria - representatives of the normal intestinal microflora - bifidobacteria (bifidumbacterin), Escherichia coli (colibacterin), lactobacilli (lactobacterin), etc.
Probiotics- drugs that have an effect when taken per os normalizing effect on the human body and its microflora.
Prebiotics - various substances that serve to nourish representatives of the norms. Microbiota and and improve intestinal motility. Eubiotics - m/o cultures that belong to the normal intestinal microbiota. For example - lactobacterin, vitoflor, linex.
immersion microscope.Immersion microscopy(from lat.immersio- immersion) - method microscopic exploration of small objects using immersion lenslight microscope Wednesday with high refractive index located between microscopic preparation and lens.
For research, special immersion lenses(lenses for oil immersion have a black stripe on the frame, close to the front lens; lenses for water immersion - white stripe).
liquid immersion
Various liquids were used for immersion microscopy. Found the most widespread Cedar oil (refractive index n=1.515), glycerol(n=1.4739) and water (distilled, n=1.3329). Saline has n=1.3346.
Water immersion. In practice, "water immersion" was widely used even before the invention of the concept itself. immersion, when lens microscope to keep an eye on the inhabitants ponds or puddles, completely immersed in water. This allows you to increase resolution lens and microscopic system as a whole.
For studies in light microscopy, special lenses for water immersion having an increased numerical aperture due to the fact that the refractive index of water is higher than that of air.
Oil immersion. Traditionally, cedar oil is used as a medium for oil immersion. However, it has a significant drawback: as it gradually oxidizes in air, it thickens, turns yellow and gradually turns into a too viscous dark liquid.
11. History of microbiology. Stages. Tasks. The history of the development of microbiology can be divided into five stages: heuristic, morphological, physiological, immunological and molecular genetic.
Pasteur made a number of outstanding discoveries. In a short period from 1857 to 1885, he proved that fermentation (lactic, alcoholic, acetic) is not a chemical process, but is caused by microorganisms; refuted the theory of spontaneous generation; discovered the phenomenon of anaerobiosis, i.e. the possibility of life of microorganisms in the absence of oxygen; laid the foundations for disinfection, asepsis and antisepsis; discovered a way to protect against infectious diseases through vaccination.
Many of L. Pasteur's discoveries have brought enormous practical benefits to mankind. By heating (pasteurization) diseases of beer and wine, lactic acid products caused by microorganisms were defeated; to prevent purulent complications of wounds, an antiseptic was introduced; Based on the principles of L. Pasteur, many vaccines have been developed to combat infectious diseases.
However, the significance of the works of L. Pasteur goes far beyond just these practical achievements. L. Pasteur brought microbiology and immunology to fundamentally new positions, showed the role of microorganisms in people's lives, economy, industry, infectious pathology, laid down the principles by which microbiology and immunology are developing in our time.
L. Pasteur was, moreover, an outstanding teacher and organizer of science.
L. Pasteur's work on vaccination opened a new stage in the development of microbiology, rightfully called immunological.
The principle of attenuation (weakening) of microorganisms using passages through a susceptible animal or by keeping microorganisms under adverse conditions (temperature, drying) allowed L. Pasteur to obtain vaccines against rabies, anthrax, chicken cholera; this principle is still used in the preparation of vaccines. Consequently, L. Pasteur is the founder of scientific immunology, although even before him the method of preventing smallpox by infecting people with cowpox, developed by the English physician E. Jenner, was known. However, this method has not been extended to the prevention of other diseases.
Robert Koch. The physiological period in the development of microbiology is also associated with the name of the German scientist Robert Koch, who developed methods for obtaining pure cultures of bacteria, staining bacteria during microscopy, and microphotography. Also known is the Koch triad formulated by R. Koch, which is still used in establishing the causative agent of the disease.
Tasks. - study of the biological properties of pathogenic organisms - development of methods for diagnosing the types of diseases caused - development of methods for combating pathogenic m/o - creation of methods for stimulating m/o that are useful for humans
bacterial cell comprises cell wall, the cytoplasmic membrane, the cytoplasm with inclusions, and the nucleus, called the nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria under adverse conditions are able to form spores.
cell wall. In the cell wall gram-positive bacteria contains a small amount of polysaccharides, lipids, proteins. The main component of the thick cell wall of these bacteria is a multilayer peptidoglycan (murein, mucopeptide), which makes up 40-90% of the mass of the cell wall. Teichoic acids (from the Greek. teichos- wall).
Into the cell wall Gram-negative bacteria enters the outer membrane, connected by means of a lipoprotein to the underlying layer of peptidoglycan. On ultrathin sections of bacteria, the outer membrane has the form of a wavy three-layer structure similar to the inner membrane, which is called cytoplasmic. The main component of these membranes is a bimolecular (double) layer of lipids. The inner layer of the outer membrane is represented by phospholipids, and the outer layer contains lipopolysaccharide.
Functions of the cell wall :
Determines the shape of the cell.
Protects the cell from mechanical damage from the outside and withstands significant internal pressure.
It has the property of semi-permeability, therefore nutrients selectively penetrate through it from the environment.
Carries on its surface receptors for bacteriophages and various chemicals.
Cell wall detection method- electron microscopy, plasmolysis.
L-forms of bacteria, their medical significance L-forms are bacteria completely or partially devoid of a cell wall (protoplast +/- cell wall residue), therefore, they have a peculiar morphology in the form of large and small spherical cells. Capable of reproduction.
14. Methods of cultivation of viruses. Virological method. For the cultivation of viruses, cell cultures, chicken embryos and sensitive laboratory animals are used. The same methods are also used for the cultivation of rickettsia and chlamydia, obligate intracellular bacteria that do not grow on artificial nutrient media.
Cell cultures. Cell cultures are prepared from animal or human tissues. Cultures are divided into primary (non-transplantable), semi-transplantable and transplantable.
Preparation of primary cell culture consists of several successive stages: tissue grinding, separation of cells by trypsinization, washing the resulting homogeneous suspension of isolated cells from trypsin, followed by suspension of the cells in a nutrient medium that ensures their growth, for example, in medium 199 with the addition of calf blood serum.
Transplanted crops in contrast to the primary ones, they are adapted to conditions that ensure their permanent existence in vitro and persist for several dozen passages.
Continuous single-layer cell cultures are prepared from malignant and normal cell lines that have the ability to multiply in vitro for a long time under certain conditions. These include malignant HeLa cells originally isolated from cervical carcinoma, Hep-3 (from lymphoid carcinoma), as well as normal human amnion cells, monkey kidneys, etc.
To semi-perennial crops are human diploid cells. They represent a cellular system that preserves during 50 passages (up to a year) a diploid set of chromosomes, typical for somatic cells fabric used. Diploid human cells do not undergo malignant transformation and this compares favorably with tumor cells.
About reproduction (reproduction) of viruses in cell culture judged by the cytopathic effect (CPE), which can be detected microscopically and is characterized by morphological changes in cells.
The nature of the CPD of viruses is used both for their detection (indication) and for tentative identification, i.e., determining their species.
One of the methods The indication of viruses is based on the ability of the surface of the cells in which they reproduce to adsorb erythrocytes - the hemadsorption reaction. To put it into a culture of cells infected with viruses, a suspension of erythrocytes is added, and after some time of contact, the cells are washed with isotonic sodium chloride solution. Adhering erythrocytes remain on the surface of virus-affected cells.
Another method is the hemagglutination reaction (RG). It is used to detect viruses in the culture fluid of cell culture or chorionallantoic or amniotic fluid of a chicken embryo.
The number of viral particles is determined by titration by CPE in cell culture. To do this, culture cells are infected with a tenfold dilution of the virus. After 6-7 days of incubation, they are examined for the presence of CPP. The highest dilution that causes CPE in 50% of infected cultures is taken as the virus titer. The virus titer is expressed as the number of cytopathic doses.
more accurate quantitative method accounting for individual viral particles is the plaque method.
Some viruses can be detected and identified by inclusions that they form in the nucleus or cytoplasm of infected cells.
Chicken embryos. Chicken embryos, compared with cell cultures, are much less likely to be contaminated with viruses and mycoplasmas, and also have a relatively high viability and resistance to various influences.
To obtain pure cultures of rickettsia, chlamydia and a number of viruses for diagnostic purposes, as well as for the preparation of various preparations (vaccines, diagnosticums), 8-12-day-old chicken embryos are used. The reproduction of the mentioned microorganisms is judged by morphological changes detected after opening the embryo on its membranes.
The reproduction of some viruses, such as influenza, smallpox, can be judged by the hemagglutination reaction (RHA) with chicken or other erythrocytes.
The disadvantages of this method include the impossibility of detecting the studied microorganism without first opening the embryo, as well as the presence in it of a large amount of proteins and other compounds that make it difficult to further purify rickettsiae or viruses in the manufacture of various preparations.
laboratory animals. Species sensitivity of animals to a particular virus and their age determine the reproductive ability of viruses. In many cases, only newborn animals are sensitive to a particular virus (for example, suckling mice are susceptible to Coxsackie viruses).
The advantage of this method over others is the possibility of isolating those viruses that are poorly reproduced in culture or in the embryo. Its disadvantages include contamination of the body of experimental animals with foreign viruses and mycoplasmas, as well as the need for subsequent infection of the cell culture to obtain a pure line of this virus, which prolongs the study period. The virological method includes the cultivation of viruses, their indication and identification. Materials for virological research can be blood, various secrets and excretions, biopsies of human organs and tissues. Blood tests are often performed to diagnose arbovirus diseases. In saliva, rabies, mumps, and herpes simplex viruses can be detected. Nasopharyngeal swabs are used to isolate the causative agent of influenza, measles, rhinoviruses, respiratory syncytial virus, adenoviruses. In washings from the conjunctiva, adenoviruses are found. Various enteroviruses, adeno-, reo- and rotaviruses are isolated from feces. Cell cultures, chicken embryos, and sometimes laboratory animals are used to isolate viruses. The source of cells is tissues extracted from a person during surgery, organs of embryos, animals and birds. Normal or malignantly degenerated tissues are used: epithelial, fibroblastic type and mixed. Human viruses reproduce best in cultures of human or monkey kidney cells. Most pathogenic viruses are distinguished by the presence of tissue and type specificity. For example, poliovirus reproduces only in primate cells, which determines the need to select an appropriate culture. To isolate an unknown pathogen, it is advisable to simultaneously infect 3-4 cell cultures, since one of them may be sensitive. fifteen. Microscopy methods (fluorescent, dark-field, phase-contrast, electron).
Luminescent (or fluorescent) microscopy. Based on the phenomenon of photoluminescence.
Luminescence- the glow of substances that occurs after exposure to any energy sources: light, electron beams, ionizing radiation. Photoluminescence- luminescence of an object under the influence of light. When a luminescent object is illuminated with blue light, it emits rays of red, orange, yellow, or green. The result is a color image of the object. The luminescent method of microscopy occupies an important place in the study of microorganisms. Luminescence (or fluorescence) is the emission of light by a cell due to the absorbed energy. Only a few bacteria (luminescent) are able to glow with their own light as a result of intense oxidation processes that occur in them with a significant release of energy.
Most microorganisms acquire the ability to luminesce, or fluoresce, when illuminated with ultraviolet rays after preliminary staining with special dyes - fluorochromes. By absorbing short ultraviolet wavelengths, an object emits longer wavelengths of the visible spectrum. As a result, the resolution of the microscope is increased. This makes it possible to study smaller particles. Fluorochrome dyes are more often used: acridine orange, auramine, corifosphine, fluorescein in the form of very weak aqueous solutions.
When stained with Corifosphine, diphtheria corynebacteria give a yellow-green glow in ultraviolet light, Mycobacterium tuberculosis when stained with auramine-rhodamine - golden-orange. Successful microscopy requires a bright light source, which is a high-pressure mercury-quartz lamp. A blue-violet light filter is placed between the light source and the mirror, which allows only short and medium wavelengths of ultraviolet light to pass through. Once on the lens, these waves excite luminescence in it. To see it, a yellow filter is put on the eyepiece of the microscope, which transmits the long-wavelength fluorescence light that occurs when the rays pass through the object. Short waves not absorbed by the object under study are removed and cut off by this filter.
There are special luminescent microscopes ML-1, ML-2, ML-3, as well as simple devices: a set of OI-17 (opacilluminator), OI-18 (illuminating device with a mercury-quartz lamp SVD-120A), which make it possible to use for fluorescent microscopy conventional biological microscope.
dark field microscopy. Microscopy in a dark field of vision is based on the phenomenon of light diffraction under strong side illumination of tiny particles suspended in a liquid (Tyndall effect). The effect is achieved using a paraboloid or cardioid condenser, which replaces a conventional condenser in a biological microscope. The study of microorganisms in a dark field (dark field microscopy) is based on the phenomena of light scattering under strong side illumination of particles suspended in a liquid. Dark field microscopy allows you to see smaller particles than in a light microscope. It is carried out using a conventional light microscope equipped with special condensers (paraboloid or cardioid condenser), which creates a hollow cone of light. The top of this hollow cone coincides with the object. Rays of light, passing through the object of study in an oblique direction, do not fall into the microscope objective. Only the light scattered by the object penetrates into it. Therefore, against the dark background of the preparation, brightly luminous contours of microbial cells and other particles are observed. Dark field microscopy allows determine the shape of the microbe and its mobility. Typically, dark-field microscopy is used in the study of microorganisms that weakly absorb light and are not visible under a light microscope, such as spirochetes. To create a dark field, you can also use a regular Abbe condenser by placing a circle of black paper in its center. In this case, the light is set and centered on the light field, and then the Abbe condenser is darkened. The preparation for microscopy is prepared according to the crushed drop method. The thickness of the slide should not exceed 1 - 1.1 mm, otherwise the focus of the condenser will be in the thickness of the glass. A liquid (distilled water) with a refractive index close to that of glass is placed between the condenser and the glass slide. When the lighting is set correctly, bright luminous dots are visible on a dark field.
Phase contrast microscopy. The phase-contrast device makes it possible to see transparent objects in a microscope. They acquire a high image contrast, which can be positive or negative. Positive phase contrast is a dark image of an object in a bright field of view, negative phase contrast is a bright image of an object against a dark background.
For phase-contrast microscopy, a conventional microscope and an additional phase-contrast device, as well as special illuminators, are used. The human eye can pick up changes in the wavelength and intensity of visible light only when examining opaque objects, passing through which light waves are uniformly or unevenly attenuated, i.e., change the magnitude of the amplitude. Such objects are called amplitude. Usually these are fixed and stained preparations of microorganisms or tissue sections. Living cells, due to their high water content, weakly absorb light, so almost all of their components are transparent.
The method of phase-contrast microscopy is based on the fact that living cells and microorganisms, which weakly absorb light, are nevertheless capable of changing the phase of the rays passing through them (phase objects). In different parts of cells that differ in refractive index and thickness, the phase change will be different. These phase differences, which occur when visible light passes through living objects, can be made visible using phase contrast microscopy.
Phase-contrast microscopy is carried out using a conventional light microscope and a special device, which includes a phase-contrast condenser with annular diaphragms and a ring-shaped phase plate. For initial aiming, an auxiliary microscope is used, with the help of which it is ensured that only a ring of light penetrates into the lens through the annular diaphragm of the condenser. A beam of light passing through a transparent object splits into two beams: direct and diffracted (refracted). The direct beam, having penetrated the particle, is focused on the ring of the phase plate, and the diffracted beam, as it were, goes around the particle without passing through it. Therefore, their optical paths are different and a phase difference is created between them. It is greatly increased with the help of a phase plate, and due to this, the contrast of the image is increased, which makes it possible to observe not only phase objects as a whole, but also structural details, for example, living cells and microorganisms.
Electron microscopy. Allows you to observe objects whose dimensions are beyond the resolution of a light microscope (0.2 microns). An electron microscope is used to study viruses, the fine structure of various microorganisms, macromolecular structures and other submicroscopic objects.
16. Methods for determining the sensitivity of bacteria to antibiotics. To determine the sensitivity of bacteria to antibiotics (antibiograms) usually used:
Agar diffusion method. On agar nutrient medium the test microbe is inoculated, and then antibiotics are applied. Usually, drugs are applied either to special wells in agar, or discs with antibiotics are laid out on the surface of the seed (the “disc method”). The results are recorded in a day by the presence or absence of microbial growth around the holes (discs). Disk method - qualitative and allows you to assess whether the microbe is sensitive or resistant to the drug.
Methods of determination minimum inhibitory and bactericidal concentrations, i.e., the minimum level of antibiotic that prevents the visible growth of microbes in the nutrient medium or completely sterilizes it. it quantitative methods that allow you to calculate the dose of the drug, since the concentration of the antibiotic in the blood must be significantly higher than the minimum inhibitory concentration for the infectious agent. The introduction of adequate doses of the drug is necessary for effective treatment and prevention of the formation of resistant microbes.
There are accelerated methods using automatic analyzers.
Determination of the sensitivity of bacteria to antibiotics using the disk method. The studied bacterial culture is seeded with a lawn on nutrient agar or AGV medium in a Petri dish.
AGV medium: dry nutrient fish broth, agar-agar, dibasic sodium phosphate. The medium is prepared from a dry powder in accordance with the instructions.
Paper discs containing certain doses of different antibiotics are placed on the seeded surface with tweezers at the same distance from each other. The cultures are incubated at 37°C until the next day. According to the diameter of the growth inhibition zones of the studied bacterial culture, its sensitivity to antibiotics is judged.
To obtain reliable results, it is necessary to use standard discs and nutrient media, for the control of which reference strains of the relevant microorganisms are used. The disc method does not provide reliable data for determining the sensitivity of microorganisms to polypeptide antibiotics that diffuse poorly into agar (for example, polymyxin, ristomycin). If these antibiotics are to be used for treatment, it is recommended to determine the sensitivity of microorganisms by the method of serial dilutions.
Determination of the sensitivity of bacteria to antibiotics by the method of serial dilutions. This method determines the minimum concentration of the antibiotic that inhibits the growth of the studied bacterial culture. First, a stock solution is prepared containing a specific concentration of the antibiotic (µg/ml or IU/ml) in a special solvent or buffer solution. All subsequent dilutions in broth are prepared from it (in a volume of 1 ml), after which 0.1 ml of the studied bacterial suspension containing 10 6 -10 7 bacterial cells per 1 ml is added to each dilution. Add 1 ml of broth and 0.1 ml of bacterial suspension to the last tube (culture control). The inoculations are incubated at 37 °C until the next day, after which the results of the experiment on the turbidity of the nutrient medium are noted, compared with the culture control. The last tube with a transparent nutrient medium indicates a growth retardation of the studied bacterial culture, under the influence of the minimum inhibitory concentration (MIC) of the antibiotic contained in it.
The evaluation of the results of determining the sensitivity of microorganisms to antibiotics is carried out according to a special ready-made table, which contains the boundary values of the diameters of the growth inhibition zones for resistant, moderately resistant and sensitive strains, as well as the MIC values \u200b\u200bof antibiotics for resistant and sensitive strains.
strains are susceptible microorganisms whose growth is inhibited at concentrations of the drug found in the patient's blood serum when using normal doses of antibiotics. The moderately resistant strains are, to suppress the growth of which requires concentrations that are created in the blood serum with the introduction of maximum doses of the drug. Microorganisms are resistant, the growth of which is not suppressed by the drug in concentrations created in the body when using the maximum allowable doses.
Determination of an antibiotic in blood, urine and other body fluids. Two rows of test tubes are placed in a rack. In one of them, dilutions of the reference antibiotic are prepared, in the other, the test liquid. Then, a suspension of test bacteria prepared in Hiss medium with glucose is added to each test tube. When determining penicillin, tetracyclines, erythromycin in the test liquid, a standard strain of S. aureus is used as test bacteria, and when determining streptomycin, E. coli is used. After incubation of the inoculations at 37 °C for 18-20 hours, the results of the experiment on cloudiness of the medium and its staining with an indicator due to the breakdown of glucose by test bacteria are noted. The antibiotic concentration is determined by multiplying the highest dilution of the test fluid that inhibits the growth of test bacteria by the minimum concentration of the reference antibiotic that inhibits the growth of the same test bacteria. For example, if the maximum dilution of the test liquid that inhibits the growth of test bacteria is 1:1024, and the minimum concentration of the reference antibiotic that inhibits the growth of the same test bacteria is 0.313 µg/ml, then the product of 1024x0.313=320 µg/ml is the concentration antibiotic in 1 ml.
Determination of the ability of S. aureus to produce beta-lactamase. In a flask with 0.5 ml of a daily broth culture of a standard strain of staphylococcus sensitive to penicillin, add 20 ml of molten and cooled to 45 ° C nutrient agar, mix and pour into a Petri dish. After the agar has solidified, a disk containing penicillin is placed in the center of the dish on the surface of the medium. The studied cultures are sown along the disk radii with a loop. The inoculations are incubated at 37 °C until the next day, after which the results of the experiment are noted. The ability of the studied bacteria to produce beta-lactamase is judged by the presence of growth of a standard strain of staphylococcus around one or another of the studied cultures (around the disk).
Biologists call bacteria an evolutionary recipe for success - they are so resistant to any conditions external environment. Some of them feel great even with lethal doses of radiation.
Microbiologist John Batista of the University of Louisiana has seen a lot. However, about his first encounter with a microbe, jokingly nicknamed "Superbug Conan", he said: "Honestly, it was not easy for me to believe in the reality of the existence of such an organism."
In the early 1960s, Thomas Brock discovered bacteria in Yellowstone National Park that could withstand temperatures close to boiling point. After that, microbiologists began to find more and more new types of extreme microbes. However, Conan has surpassed all: the most resistant microorganism, it withstands harsh frost, sizzling heat, acid baths and poisons. But most striking of all was his reaction to high doses of radiation exposure. Even a 1500-fold excess of a dose that is lethal to other organisms did no harm to the bacteria.
Conan was first discovered in the 1950s in spoiled canned meat destined for the army. To protect against bacterial contamination, canned food in the United States is usually sterilized using radioactive radiation. Scientists were all the more surprised when they saw pink mold in the jars with the smell of rotten cabbage, clearly of bacterial origin. They were puzzled. After all, radiation usually causes deep damage to the genetic material in living organisms. If the amount of such damage exceeds a certain critical level the microorganism dies. But for Conan the law is not written. What mechanisms save a nondescript crumb from death in any situation?
The baffled microbiologists set about unraveling the mystery of Conan. They examined his genetic material before and after exposure to radiation and analyzed metabolic processes. To their surprise, the results showed that Conan also suffered greatly from radiation, but at the same time knew how to overcome its disastrous effects.
If some poisons or ionizing radiation cause relatively minor damage to only one of the two DNA strands of an organism, then radioactive radiation causes damage to both strands of DNA, and their restoration is often unbearable for the organism. So, for the death of E. coli living in the human intestine, two or three such DNA damages are enough.
Conan, on the contrary, quickly restored two hundred such "breakdowns". The fact is that in the process of evolution, he developed effective mechanisms restoration of gene damage - including a special enzyme that looks for suitable "spare parts" in the hereditary material, copies them and pastes them into the damaged areas.
Conan's DNA recovery is facilitated by another circumstance: Conan's genome consists of four circular DNA molecules, and in each cell the genome is present not in one, as in most bacteria, but in several copies. It is thanks to these copies that the damaged areas are restored. Since the cell is most vulnerable to radiation at the time of division, when the circular DNA molecule must open, Conan developed another method of protection: the bacterium leaves three molecules folded into a ring, and uses the fourth for reproduction needs. If this chromosome is damaged by radiation, the spare chromosomes serve as templates from which the body copies the correct gene sequences.
In 2007, microbiologist Michael J. Daley discovered another reason for Conan's hypertolerance: the bacterium has an incredibly high intracellular concentration of manganese, an element that also helps repair DNA damage.
And yet, despite the discoveries made, the mystery of Conan's super-resistance to radiation has not yet been fully solved. Research is in full swing: scientists hope to effectively use Konan to clean up soils contaminated with radiation.
ovation. The temperature range at which the growth of psychrophilic bacteria is possible ranges from -10 to 40 °C, and the temperature optimum - 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 of 10-47 °C; the optimum growth for most of them is 37 °C.
At higher temperatures (from 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, participate in the processes of self-heating of manure, grain, 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 as an indicator of soil contamination.
The temperature factor is taken into account during sterilization. Vegetative forms of bacteria die at a temperature of 60 °C within 20-30 minutes; spores - in an autoclave at 120 ° C under steam pressure.
Microorganisms withstand low temperatures well. Therefore, they can be stored frozen for a long time, including at liquid gas temperature (-173 °C).
Drying. Dehydration causes disruption of the functions 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 up to 90 days. Some capsulo- and mucus-forming bacteria are resistant to drying. But bacterial spores are particularly resistant.
Drying under vacuum from a frozen state - lyophilization - is used to prolong the viability, preservation of microorganisms. Lyophilized cultures of microorganisms and immunobiological preparations are stored for a long time (for several years) without changing their original properties.
Radiation action. Non-ionizing radiation - ultraviolet and infrared rays of sunlight, as well as ionizing radiation - gamma radiation 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, microbiological laboratories. For this purpose, bactericidal lamps of UV radiation with a wavelength of 200-450 nm are used.
Ionizing radiation is used to sterilize disposable plastic microbiological utensils, nutrient media, dressings, drugs, etc. However, there are bacteria that are resistant to ionizing radiation, for example, Micrococcus radiodurans was isolated from a nuclear reactor.
The action of chemicals. Chemicals can have different effects on microorganisms: serve as food sources; not exert any influence; stimulate or inhibit 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 be bactericidal, virucidal, fungicidal, etc.
Chemicals 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, dezam, chlordesin, sulfochloranthin, etc. Iodopyrine and dibromantine are considered promising antimicrobial drugs based on iodine and bromine. Intensive oxidizing agents are hydrogen peroxide, potassium permanganate, etc. They have a pronounced bactericidal effect.
Phenols and their derivatives include phenol, lysol, lyso-id, creosote, creolin, chloro-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, children's institutions, catering establishments 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, ampholane, etc.).
For disinfection of precision instruments (e.g. spaceships), as well as equipment and apparatus, use a gas mixture of ethylene oxide with methyl bromide. Disinfection is carried out in hermetic conditions.
Influence of biological factors. Microorganisms are with each other in various relationships. The joint existence of two different organisms is called symbiosis (from the Greek simbiosis - living together). There are several variants of useful relationships: metabiosis, mutualism, commensalism, satelliteism.
Metabiosis - the relationship between microorganisms, in which one microorganism uses the waste products of another organism for its life. Metabiosis is characteristic of soil nitrifying bacteria that 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 - companion) - cohabitation of individuals different types in which one species benefits from the symbiosis without harming the other. Commensals are bacteria, representatives of the normal human microflora.
Satelliteism 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 faster 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. Microorganisms-antagonists are common in soil, water and human and animal organisms. The antagonistic activity of representatives of the normal microflora of the human large intestine - bifidobacteria, lactobacilli, Escherichia coli, etc., which are antagonists of the putrefactive microflora, is well known.
The mechanism of antagonistic relationships is diverse. A common form of antagonism is the formation of antibiotics - specific metabolic products of microorganisms that inhibit 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 medium.
4.7. Microflora of plant medicinal raw materials, phytopathogenic microorganisms, microbiological control of medicines
Herbal medicinal raw materials can be contaminated with microorganisms in the process of its production: infection occurs through water, non-sterile pharmacy utensils, the air of industrial premises and the hands of personnel. Insemination also occurs due to the normal microflora of plants and phytopathogenic microorganisms - pathogens of plant diseases. Phytopathogenic microorganisms are able to spread and infect a large number of plants.
Microorganisms that normally develop on the surface of plants are epiphytes (Greek epi - above, phyton - plant). They do no harm, are antagonists of some phytopathogenic microorganisms, grow at the expense of normal plant secretions and organic pollution of plant surfaces. Epiphytic microflora prevents the penetration of phytopathogenic microorganisms into plant tissues, thereby enhancing plant immunity. The largest number of epiphytic microflora are 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 in the norm - Pseudomonas fluorescens, less often Bacillus mesentericus and a small amount of fungi. Microorganisms are found not only on the leaves, stems, but also on the seeds of plants. Violation of the surface of plants and their seeds contributes to the accumulation of a large amount of dust and microorganisms on them. The composition of plant microflora depends on the species, plant age, soil type and ambient temperature. With an increase in humidity, the number of epiphytic microorganisms increases, with a decrease in humidity, it decreases.
In the soil, near the roots of plants, there is a significant amount
Changes in environmental conditions affect the vital activity of microorganisms. physical, chemical, biological factors environments can accelerate or inhibit the development of microbes, can change their properties or even cause death.
The environmental factors that have the most noticeable effect on are humidity, temperature, acidity and chemical composition of the environment, the action of light and other physical factors.
Humidity
Microorganisms can live and develop only in an environment with a certain moisture content. Water is necessary for all metabolic processes of microorganisms, for normal osmotic pressure in a microbial cell, to maintain its viability. Different microorganisms have different water requirements. Bacteria are mainly hygrophilous; when the humidity of the environment is below 20%, their growth stops. For molds, the lower limit of environmental humidity is 15%, and with significant air humidity it is even lower. The settling of water vapor from the air on the surface of the product promotes the growth of microorganisms.
With a decrease in the water content in the medium, the growth of microorganisms slows down and may completely stop. Therefore, dry foods can be stored much longer than foods with high moisture content. Drying food allows you to keep food at room temperature without refrigeration.
Some microbes are very resistant to drying, and some bacteria and yeasts can survive up to a month or more when dried. Spores of bacteria and mold fungi remain viable in the absence of moisture for tens, and sometimes hundreds of years.
Temperature
Temperature is the most important factor for the development of microorganisms. For each of the microorganisms there is a minimum, optimum and maximum temperature regime for growth. According to this property, microbes are divided into three groups:
- psychrophiles - microorganisms that grow well at low temperatures with a minimum at -10-0 °C, an optimum at 10-15 °C;
- mesophiles - microorganisms for which the optimum growth is observed at 25-35 °C, the minimum - at 5-10 °C, the maximum - at 50-60 °C;
- thermophiles - microorganisms that grow well at relatively high temperatures with an optimum growth at 50-65 °C, a maximum at temperatures above 70 °C.
Most microorganisms belong to mesophiles, for the development of which the temperature of 25-35 °C is optimal. Therefore, the storage of food products at this temperature leads to the rapid multiplication of microorganisms in them and the deterioration of products. Some microbes with significant accumulation in foods can lead to human food poisoning. Pathogenic microorganisms, i.e. defiant infectious diseases humans are also mesophilic.
Low temperatures slow down the growth of microorganisms, but do not kill them. In chilled food products, the growth of microorganisms is slow, but continues. At temperatures below 0 ° C, most microbes stop multiplying, i.e. when food is frozen, the growth of microbes stops, some of them gradually die off. It has been established that at temperatures below 0 °C, most microorganisms fall into a state similar to anabiosis, retain their viability, and continue their development when the temperature rises. This property of microorganisms should be taken into account during storage and further culinary processing of food products. For example, salmonella can be stored in frozen meat for a long time, and after defrosting the meat, under favorable conditions, they quickly accumulate to a dangerous amount for humans.
When exposed to high temperatures, exceeding the maximum endurance of microorganisms, their death occurs. Bacteria that do not have the ability to form spores die when heated in a humid environment to 60-70 ° C after 15-30 minutes, to 80-100 ° C - after a few seconds or minutes. Bacterial spores are much more resistant to heat. They are able to withstand 100 ° C for 1-6 hours, at a temperature of 120-130 ° C bacterial spores die in a humid environment in 20-30 minutes. Mold spores are less heat resistant.
Thermal culinary treatment of food products in public catering, pasteurization and sterilization of products in the food industry lead to partial or complete (sterilization) death of vegetative cells of microorganisms.
During pasteurization, the food product is subjected to a minimum temperature effect. Depending on the temperature regime, low and high pasteurization are distinguished.
Low pasteurization is carried out at a temperature not exceeding 65-80 ° C, for at least 20 minutes to better guarantee the safety of the product.
High pasteurization is a short-term (no more than 1 minute) exposure of the pasteurized product to a temperature above 90 ° C, which leads to the death of pathogenic non-spore-bearing microflora and at the same time does not entail significant changes in the natural properties of the pasteurized products. Pasteurized foods cannot be stored without refrigeration.
Sterilization involves the release of the product from all forms of microorganisms, including spores. Sterilization of canned food is carried out in special devices - autoclaves (under steam pressure) at a temperature of 110-125 ° C for 20-60 minutes. Sterilization provides the possibility of long-term storage of canned food. Milk is sterilized by ultra-high temperature treatment (at temperatures above 130 ° C) within a few seconds, which allows you to save all beneficial features milk.
Environment reaction
The vital activity of microorganisms depends on the concentration of hydrogen (H +) or hydroxyl (OH -) ions in the substrate on which they develop. For most bacteria, a neutral (pH about 7) or slightly alkaline environment is most favorable. Molds and yeast grow well in a slightly acidic environment. High acidity of the environment (pH below 4.0) inhibits the development of bacteria, but molds can continue to grow in a more acidic environment. The suppression of the growth of putrefactive microorganisms during acidification of the medium has practical applications. The addition of acetic acid is used when pickling products, which prevents the processes of decay and allows you to save food. The lactic acid formed during fermentation also inhibits the growth of putrefactive bacteria.
Salt and sugar concentration
Table salt and sugar have long been used to increase the resistance of foods to microbial spoilage and to improve food preservation.
Some microorganisms require high concentrations of salt (20% or more) for their development. They are called salt-loving, or halophiles. They can spoil salty foods.
High concentrations of sugar (above 55-65%) stop the reproduction of most microorganisms; this is used in the preparation of jam, jam or marmalade from fruits and berries. However, these products can also be spoiled by osmophilic molds or yeasts.
Light
Some microorganisms need light for normal development, but for most of them it is detrimental. The ultraviolet rays of the sun have a bactericidal effect, i.e., at certain doses of radiation, they lead to the death of microorganisms. The bactericidal properties of ultraviolet rays of mercury-quartz lamps are used to disinfect air, water, and some food products. Infrared rays can also cause the death of microbes due to thermal exposure. The impact of these rays is used in the heat treatment of products. Negative impact on microorganisms can have electromagnetic fields, ionizing radiation and other physical factors of the environment.
Chemical Factors
Some chemicals can have a detrimental effect on microorganisms. Bactericidal chemicals are called antiseptics. These include disinfectants (chlorine, hypochlorites, etc.) used in medicine, food industry and public catering enterprises.
Some antiseptics are used as food additives(sorbic and benzoic acids, etc.) in the manufacture of juices, caviar, creams, salads and other products.
Biological factors
The antagonistic properties of some are explained by the ability to isolate them in environment substances with antimicrobial (bacteriostatic, bactericidal or fungicidal) action - antibiotics. Antibiotics are produced mainly by fungi, rarely by bacteria, they have their own specific effect on certain types of bacteria or fungi (fungicidal action). Antibiotics are used in medicine (penicillin, chloramphenicol, streptomycin, etc.), in animal husbandry as a feed additive, and in the food industry for food preservation (nisin).
Phytoncides have antibiotic properties - substances found in many plants and foods (onion, garlic, radish, horseradish, spices, etc.). Phytoncides include essential oils, anthocyanins and other substances. They are able to cause the death of pathogenic microorganisms and putrefactive bacteria.
Egg white, fish caviar, tears, saliva contain lysozyme, an antibiotic substance of animal origin.