Factors affecting microbial growth and death

Growth is the result of the combination of microorganisms and external environmental factorsChanges in environmental conditions can cause changes in microbial morphology, physiology, growth, reproduction and other characteristics, or resist and adapt to certain changes in environmental conditions, and when changes in environmental conditions exceed certain limits, the death of microorganisms can be causedIn order to inhibit and eliminate the harmful effects of microorganisms, a variety of physical, chemical or biological methods are often used to suppress or kill microorganismsThe following terms are commonly used to indicate the degree of killing of microorganisms"text-align:center;"img src""alt"""alt"""factors affecting microbial growth and death"title":sterilization: physical or chemical methods to kill all microorganisms on the object (including pathogenic microorganisms and non-pathogenic microorganisms and bacterial spores, mold spores, etc.) called sterilizationdisinfection: physical or chemical methods can only kill pathogenic microorganisms on the object, while non-pathogenic microorganisms and buds and spores do not necessarily kill completely, called disinfectionThe drug used for disinfection is called a disinfectantantiseptic seis: A method of preventing or inhibiting microbial growth and reproduction is called anti-corrosion or antisepticChemicals used for anti-corrosion are called preservativesSome chemicals are preservatives at low concentrations and disinfectants at high concentrationssterile: the absence of living microorganismsA method of preventing or preventing all microorganisms from entering an animal body or object is called asepticIt is called aseptic operation when operated by aseptic methodIn surgical or microbiological experiments, strict aseptic operations are required to prevent microbial contaminationdifferent microorganisms are sensitive to various physical and chemical factors, the same factor different doses of the effect on microorganisms are also different, or play a sterilization effect, or may only be disinfection or antiseptic effectIn understanding and applying the inhibitory or lethal effect of any kind of physical and chemical factor on microorganisms, the combined effects of many factors should also be taken into account For example, adding another chemical to increase the temperature can accelerate the destructive effects on microorganisms In the presence of phenol, the temperature of E coli increased from 30 degrees C to 42 degrees C significantly accelerated death; Nutritional cells are generally less resistant than spores, and young, metabolically active cells are more likely to be destroyed than aging, dormant cells; For example, in acid sourcin or alkali, the damage of heat to microorganisms increases, the viscosity of the medium also affects the penetration ability of antibacterial factors, the presence of organic matter also interferes with the effect of antimicrobial chemical factors, or because of the combination of organic matter and chemicalagents to make it fail, or the organic matter covers the cell surface, hindering the infiltration of chemicalagents common physical and chemical factors that affect microbial growth and death are: 1, temperature: temperature is one of the most important factors affecting the growth and survival of organisms Its effect on the living organism is manifested in two aspects: on the one hand, as the temperature rises, the rate of biochemical reactions and growth rates in cells increase In general, the biochemical reaction rate doubles for every 10 degrees C increase in temperature, and on the other hand, important components of the body, such as proteins and nucleic acids, are more sensitive to temperature, and may suffer irreversible damage as the temperature increases Therefore, only within a certain range, the body's metabolic activity and growth and reproduction with the temperature increase, when the temperature rises to a certain extent, began to adversely affect the body, such as further rise, then the cell function dropped sharply to death in general, the temperature range of microbial growth is wide, and known microorganisms can grow at minus 12-100 degrees Celsius Each microorganism can only grow within a certain temperature range All microorganisms have the lowest temperature, the optimum temperature, the maximum temperature and the lethal temperature Minimum growth temperature: refers to the minimum temperature limit for microbial reproduction, and if it is below this temperature, the growth stops completely The most suitable growth temperature: the temperature at which the micro-organisms can grow and reproduce rapidly is called the most suitable growth temperature, at which temperature, the microbial population grows and reproduces the fastest, the shortest time The optimum growth temperature of different microorganisms is different Maximum growth temperature: refers to the maximum temperature limit for microbial growth and reproduction Fatal temperature: If the maximum growth temperature is raised further, it kills the microorganism, the minimum temperature limit of the deadly microorganism is the lethal temperature, which is related to the treatment time Micro-organisms can be divided into low-temperature microorganisms, medium-temperature microorganisms and high temperature microorganisms according to their growth temperature range As shown in the table: "? "text-align: center;" "img src""alt" "Factors affecting microbial growth and death" title"," 2, hydrogen ion concentration (pH): the acidity in the environment is usually expressed as a negative pair of hydrogen ion concentrations, i.e pH The pH in the environment has a great influence on the life activity of microorganisms, the main effects are: causing the change of cell membrane charge, which affects the absorption of nutrients by microorganisms, affecting the activity of enzymes in the metabolic process, changing the feeding properties of nutrients in the growing environment and the toxicity of harmful substances each microorganism has its most pH and a certain pH range Enzyme activity is highest in the most suitable range and, if other conditions are appropriate, the growth rate of microorganisms is highest Most bacteria, algae and protozoa have the most suitable pH of 6.5-7.5 and can grow between pH 4-10; Some bacteria can even live in strong acidic or alkaline environments microbes grow in the matrix, and metabolism changes the concentration of hydrogen ions in the matrix As the ambient pH is constantly changing, microbial growth is blocked and, when the minimum or maximum pH is exceeded, it can cause microbial death In order to maintain the stability of pH in microbial growth, the preparation of the medium should pay attention to adjust the pH, and often add a buffer to ensure the relative stability of pH in the microbial growth and reproduction process strong acids and alkalis have bactericidal power Although inorganic acid sterilization force is strong, but highly corrosive Some organic acids, such as benzoic acid, can be used as preservatives Strong alkali can be used as a fungicide, but because of their high toxicity, its use is limited to excreta and storage, sheds and other environment disinfection Strong alkali has a stronger effect on Gram-negative bacteria than virus-positive bacteria 3, redox potential: redox potential (s) has a significant effect on microbial growth The value of the environment is related to oxygen pressure and is also affected by pH At low pH, the redox potential is high, and when the pH is high, the redox potential is low The value required for the growth of various microorganisms is different General aerobic microorganisms can grow above the value of s.1 volts, and are appropriate when the value is .3 volts-plus 0.4 volts Anaerobic microorganisms can only grow below the value of .1 volts Also anaerobic microorganisms are actively at or above .1 volts for aerobic respiration and fermentation at a time of less than 0.1 volts 4, radiation: radiation is the energy that is transmitted from one place to another by fluctuation through air or outer space They are either ions or electromagnetic waves Electromagnetic radiation includes visible light, infrared, ultraviolet, X-ray, and gamma rays (1) Ultraviolet radiation is non-ionizing radiation, with a wavelength of 265-266 nanometers of the most bactericidal force Ultraviolet radiation has obvious lethal effect on microorganisms, is a strong fungicide, UV sterilization lamp in medical care and sterile operation is widely used Because of the poor penetration ability of ultraviolet light, not easy to pass through opaque substances, so uv sterilization lamp is only suitable for air and surface disinfection (2) Ionizing radiation X-rays and alpha-rays, beta-rays, and gamma rays are ionizing radiation At sufficient doses, it has a lethal effect on all kinds of bacteria Often used for the disinfection of disposable plastic products, but also for food disinfection 5, drying: moisture is essential to the normal life activities of microorganisms Drying can cause cells to lose water and cause metabolism to stop and die The types of microorganisms, environmental conditions, the degree of drying, etc all affect the effects of drying on microorganisms Sleep spores are also strong in anti-drying ability, in dry conditions can be long-term non-death, this characteristic has been used in the preservation of bacteria, such as the use of sand pipe to protect the spores Drying, drying and smoking are also commonly used in daily life to preserve food 6, osmosis pressure: water or other solvents through a semi-permeable membrane and diffusion phenomenon is osmosis The pressure of the solvent through the semi-permeable film during osmosis is called osmotic pressure Its size is proportional to the concentration of the solution The permeable pressure suitable for microbial growth is wide range, and they often have certain adaptability to osmotic pressure Sudden changes in osmosis pressure can cause microorganisms to become inactive, gradually change osmotic pressure, microorganisms can often adapt to this change For general microorganisms, if their cells are placed in a high-permeable solution, water will enter the solution around the cell through the cell membrane from the cell membrane, causing the cell to dehydrate and cause the mass wall to separate, making the cell unable to grow or even die Conversely, if the microorganism is placed in a low-seeing solution or water, the water in the outer environment will cause the cell to expand and even break the cell from the solution into the cell Because common microorganisms cannot tolerate high osmosis pressure, high concentrations of salt or sugar are commonly used in daily life to preserve food, such as pickled vegetables, meat and honey 7, ultrasound: ultrasound has a strong biological role The role of ultrasound is to break the cells, so that almost all microorganisms can be destroyed by it, the effect and frequency, processing time, microbial type, cell size, shape and number of people are related 8, heavy metals and their compounds: some heavy metal ions are components of microbial cells, when the concentration of these heavy metal ions in the medium is low, there is a role in promoting microbial growth, the opposite will produce toxic effects; As a result, most heavy metals and their compounds are effective fungicides or preservatives The strongest forces are Hg, Ag and Cu Such as: dichloride mercury, also known as mercury, is a highly bactericidal disinfectant A concentration of 0.1-1% of silver nitrate is commonly used for skin disinfection 9, organic compounds: have harmful effects on microorganisms organic compounds, including phenol, alcohol, aldehyde and so on can make proteindes, is a commonly used fungicides phenol: phenol, also known as stony charofic acid Their harmful effecton on bacteria may mainly make proteins denatured, but also have a surfacting effect, destroying the permeability of the cell membrane, so that the cell inclusions overflow When the concentration is high is a fatal factor, the opposite is a antibacterial effect Toluphenol is a derivative of phenol Sterilization is several times stronger than phenol The solubility of meth in water is low, but emulsions are easily formed in soap and alkaline solutions The commercially available disinfectant coalphenol soap (Lesur) is a mixture of lithofol and soap, often used 3-5% solution to disinfect the skin, tabletops and utensils alcohol: it is a dehydrator, protein denatured agent, but also a lipid solvent, can make the protein dehydrated, denatured, damage the cell membrane and have the ability to sterilize Ethanol is a commonly used disinfectant and is commonly used for the disinfection of rods, slides and other appliances in the laboratory 50-70% ethanol kills nutrient cells, 70% of ethanol is the best, more than 70% and no water alcohol is less effective formaldehyde: formaldehyde is also a commonly used bacteria and fungicides, the effect is good Pure formaldehyde is gas-like, soluble in water, commercially available Formarin solution is 37-40% formaldehyde aqueous solution 10, halogen elements and their compounds: iodine: is a strong fungicide 3-7% iodine dissolved in 70-83% ethanol formulated into iodine mite, is an effective disinfectant for skin and small wounds Iodine is generally used as an external drug chlorine or chloride: this is the most widely used disinfectant Chlorine gas is generally used for disinfection of drinking water, hypochlorite and other commonly used as disinfection in the food processing process The bactericidal mechanism of chlorine and chloride is the combination of chlorine and water to produce hypochloric acid (HClO), which is easily decomposed to produce new ecological oxygen, which is a strong oxidant, which is used to damage microorganisms 11, surfactants: substances with reduced surface tension effect seoktis called surfactants These substances are added to the medium and can affect the growth and division of microbial cells Such as soap, bleach, washing powder, etc 12, dye: dyes, especially alkaline dyes, at low concentrations can inhibit bacterial growth Because these dyes have the characteristics of selective bacteriology, they are often added to the medium with low concentrationofd dyes to be formulated into selected media For example: alkaline tribenzene methane dyes, including peacock green, bright green, crystalline purple, etc., on the Gram-positive bacteria have a strong inhibitory effect 13, chemical therapeutic agents: can directly interfere with the growth and reproduction of pathogenic microorganisms and can be used to treat infectious diseases of chemical drugs are chemical agents It selectively acts on a link in the metabolism of pathogenic microorganisms, inhibiting or killing their growth However, the human cytotoxicity is small, so it is often used for oral or injection There are many kinds of chemical therapy, which are divided into anti-metabolites and antibiotics according to their effect and properties