The effect of external factors on bacteria

So master the dependence ofmicroorganisms on the surrounding environment, in medical practice, on the one hand, can create favorable conditions to promote the growth and reproduction of microorganisms, isolate and culture pathogenic microorganisms from pathological materials, help the diagnosis of infectious diseases and prepare vaccines to prevent certain infectious diseases;

this section focuses on the adverse factors of the external environment to bacteria, and raises the awareness of disinfection and sterilization for practical application.

method of killing pathogenic microorganisms by disinfecting (Disinfection). The drug used for disinfection is called disinfectants ( Disinfectants) and is generally effective only for bacterial reproductions at common concentrations. For buds, it is necessary to increase the concentration of disinfectant and extend the effect of time.

method of sterilization to kill all microorganisms on an object, including pathogens and non-pathogens, and buds. Therefore, sterilization is more demanding than disinfection, but in daily life, the terms disinfection and sterilization are often common.

the presence of aseptic (Asepsis) objects or in containers. Sterile operation is the operating technique that prevents microorganisms from entering the body or other items. For example, in surgical or microbiological experiments, care should be taken to sterile operations.

antisepsis prevents or inhibits the growth and reproduction of microorganisms. Chemicals used for anti-corrosion are < called a href" > "preservatives. Many drugs at low concentrations only antibacterial action, concentration increase or extend the action time, there is a bactericidal effect.

sterilization and sterilization techniques depends on a number of factors. In practice, different suitable methods should be selected according to the different requirements of the object and purpose of disinfection and sterilization, as well as the different conditions.

1, physical factors

various physical factors can have a certain effect on bacteria.

(i) Thermosteric sterilization

high temperature has obvious lethal effect on bacteria. Thermal sterilization is mainly the use of high temperature to denature or solidify the bacteria, enzymes lose activity, and cause bacteria to die. However, more subtle changes have occurred before bacteria solidify. It is thought that the break of the single helix of DNA may be the main cause of death.

bugs protein", nucleic acid and other chemical structures are connected by hydrogen bonds, and hydrogen bonds are weak chemical bonds, when the bacteria are heated, hydrogen bonds are destroyed, proteins, nucleic acids, enzymes and other structures are also destroyed, loss of its biological activity, and bacterial death.

, high temperatures can also cause damage to cell membrane function and leak out small molecular substances and degraded cytosomes. The lethal effect of dry heat is not the same as that of wet heat, and is generally a toxic effect of protein denaturation, impaired oxidation and increased electrolyte level.

most reliable and commonly used in thermal sterilization, including wet and dry heat sterilization.

1. Wet heat sterilization method

At the same temperature, the sterilization effect of warmth is better than dry heat, for the following reasons:

(1) protein solidification required temperature is related to its water content, the greater the water content, the lower the temperature required for solidification. Wet and hot sterilized bacterial proteins absorb moisture, which is easy to solidify in dry and hot air at a larger temperature.

(2) steam releases a large amount of latent heat during the warm sterilization process, accelerating the increase of humidity. Therefore, wet heat sterilization is lower than dry heat, if at the same temperature, wet heat sterilization takes less time than dry heat.

(3) wet heat penetration is greater than dry heat, so that the deep can also reach sterilization temperature, so wet heat is better than dry heat.

heat sterilization method includes:

(1) boiling method: boiling 100 degrees C, 5 minutes, can kill the reproduction of ordinary bacteria. Many buds take 5 to 6 hours to die after boiling. Add 2% sodium carbonate to the water to increase its boiling point by up to 105 degrees C. It can not only promote the killing of buds, but also prevent the rust of metal vessels. Boiling method can be used for disinfection of drinking water and general equipment (knife scissors, syringes, etc.).

(2) circulating steam sterilization method: the use of about 100 degrees C of water vapor disinfection, generally using circulating steam sterilizer (the principle is equivalent to China's steamer), heating 15 to 39 minutes, can kill bacterial reproduction. The packaging of disinfection items should not be too large and too tight to help steam penetrate.

(3) intermittent sterilization method: the use of repeated circulation of steam, in order to achieve sterilization purposes. Generally used circulating steam sterilizer, 100 degrees C heating 15 to 30 minutes, can kill the breeding body; After removal, put 37 degrees C incubator overnight, so that the buds develop into a reproductive body, steaming again the next day, so that more than three times in a row. This method applies to the sterilization of nutrients that are not resistant to high temperatures < such as >a hrefs serum and medium).

(4) Pasteurization: A method of consumption that uses heat to kill pathogens or general germs in liquids without seriously impairing their quality. Created by Pasteur to disinfect alcohol, so name. Warm up 61.1 to 62.8 degrees C for half an hour, or 71.7 degrees C for 15 to 30 seconds. It is often used to disinfect milk and alcohol.

(5) high-pressure steam sterilization method: pressure steam sterilization is carried out in a specialized pressure steam sterilizer, is the most commonly used in thermal sterilization, the most reliable method. Its advantages are strong penetration, reliable sterilization effect, can kill all microorganisms.

pressure sterilizers currently in use can be divided into two categories: lower exhaust pressure sterilizers and pre-vacuum pressure sterilizers. Suitable for sterilization of high temperature and water resistant articles.

2. Dry heat sterilization requires

temperature and longer time for dry heat sterilization than wet heat sterilization.

(1) dry baking: using a dry oven, heating 160 to 180 degrees C for 2 hours, can kill all microorganisms, including bud bacteria. Mainly used in glassware, porcelain and other sterilization.

(2) burning and burning: burning is the direct use of flame to kill microorganisms, suitable for microbial laboratory vaccination needles and other non-heat metal equipment sterilization. Incineration is a thorough disinfection method, but is limited to disposing of waste contaminated items such as useless clothing, paper, garbage, etc. Incineration shall be carried out in a special incinerator.

(3) Infrared: Infrared radiation is a kind of 0.77 to 1000 micron wavelength electromagnetic wavelength, has a better thermal effect, especially 1 to 10 micron wavelength heat effect is the strongest. It is also thought to be a dry heat sterilization. Infrared light is produced by infrared light bulbs, do not need to be conducted by air, so the heating speed is fast, but the heat effect can only be generated on the surface of the irradiation, so can not make an object around the same heating. Infrared sterilization is similar to dry heat, and the temperature and time required to sterilise using infrared ovens are the same as dry roasting. Mostly used < sterilization of > devicesa href".

long-term exposure to infrared light can cause eye fatigue and headaches, and long-term exposure can cause damage to the eyes. Therefore, the working person should at least wear protective mirrors that protect against infrared injury.

(4) microwave: Microwave is a wavelength of about 1 mm to 1 m electromagnetic wave, the frequency is high, can penetrate glass, plastic film and ceramics and other substances, but not through the metal surface. Microwaves can make the media disorderly polar molecules in the microwave field, according to the frequency of the wave back and forth movement, collision and friction with each other to produce heat, the temperature of the medium can be increased, and thus at a lower temperature can play a disinfection role.

it is generally believed that its sterilization process in addition to the thermal effect, there are electromagnetic resonance effect, field effort effect and so on. There are 2450MHZ and 915MHZ microwaves commonly used in disinfection. Microwave irradiation is mostly used in food processing. In the hospital can be used for inspection room supplies, non-metallic equipment, sterile room food utensils, cups and other supplies disinfection.

long-term exposure to microwaves can cause systemic reactions such as crystal methic turbidity of the eyes, testicular damage and neurological disorders, so it must be closed before operation begins.

(ii) Electromagnetic waves and rays

1. Daylight and ultraviolet and

daylight are effective natural sterilization methods, for most microorganisms have a damaging effect, direct shooting bacteria effect is particularly good, the main factor is ultraviolet light, in addition, heat and oxygen play an auxiliary role. However, the light effect is affected by many factors, such as soot-shrouded air, glass and organic matter can reduce the bactericidal power of daylight.

ultraviolet ray is a low-energy electromagnetic radiation with a wavelength range of 240 to 280nm and an appropriate wavelength of 260nm, which is consistent with the DNA absorption spectral" range. The sterilization principle is that ultraviolet rays are easily absorbed by nuclear proteins, causing adjacent bases on the same helix of DNA to form thymus die or mutate.

ultraviolet penetration capacity is weak, can not pass through ordinary glass, dust, can only be used to disinfect the surface of objects and air, operating rooms, sterile operating laboratories and burn wards, but also can be used for non-heat resistant materials surface disinfection. Sterilization wavelength of ultraviolet rays on human skin, eyes have a damaging effect, when using should pay attention to protection.

ionizing radiation sources

high-speed electrons, X-rays and r-rays. With a high energy and penetration, can be at room temperature for heat-resistant items sterilized, so also known as "cold sterilization." The rationale is to create a free base that destroys DNA. Can be used to disinfect heat-resistant plastic syringes and catheters, etc. , can also be used for food disinfection without destroying its nutrients.

(iii) filtered sterilization method

the liquid or air through a filter containing small holes, only objects less than the aperture such as liquid and air through, objects larger than the aperture can not pass through. Mainly used in some heat-resistant serums, toxins, antibiotics, liquid medicine, air and other sterilization. The L-type of viruses, myosomes, and bacteria cannot generally be removed. Many types of filters are commonly used:

membrane filter (membrane filter) is made of nitroculose film, mounted on the filter, its aperture size is different, often used for sterilization of 0.22um. The advantage of nitro cellulose is that it is not charged, so when the liquid is filtered, the active ingredients are lost less.

Seitz is made of metal, intermediate asbestos filter, according to asbestos K, EK, EK-S three, commonly used EK sterilization.

filter is a glass fine sand heating pressed into a small dish, embedded in the glass funnel is generally G1, G2, G3, G4, G5, G6 six, G5, G6 can prevent bacteria from passing through.

the ultra-clean workstations used in laboratories and other places, that is, using the principle of filtration and sterilization to remove bacteria entering the air of the workstation.

ultrasonic and ultrasonic

sound waves that vibrate more than 200,000 times per second are not felt by the ear, known as ultrasound. Microbes are sensitive to high-intensity ultrasounds. Among them, Glorene-negative bacteria are the most sensitive, while staphylococcus is the most resistant. Although strong vibrations of sound waves can kill bacteria, there are often those who remain.

, this method has no practical value in sterilizing and sterilizing. It is mainly used to separate and extract cell parts or prepare antigens for lysed cell separation. The exacting effect of ultrasonic sterilization is not clear, and it is possible that the appearance of bacteria is caused by subtle bubbles that disrupt cell contents and destroy cell walls, resulting in bacterial disintegration and death.

(v) Dry

most bacterial reproductions die quickly when they dry in the air, such as meningococcal, gonorrhoea, Vibrio cholerae, syphilis helix, etc. Some bacteria have strong anti-drying resistance, especially when protected by proteins and other substances. Hemolytic streptococcus, for example, survives in dust for 25 days, and TB does not die in dry sputum for months.

, such as Bacillus anthrax, is more resistant to drying for more than 20 years. Drying is often used to preserve food. Strong salt or sugar-stained food, can make the bacteria body water escape, resulting in physiological dryness, so that the bacteria's life activity stopped.

(vi) low temperature

most bacteria are resistant to low temperature. At low temperatures, the metabolism of these bacteria slows down, and when the temperature returns to the appropriate range, growth and reproduction can be resumed, so low temperatures are often used as preservation strains.

II, Chemical Factors

Chemicals can affect the chemical composition, physical structure and physiological activity of bacteria, thus playing the role of anti-corrosion, disinfection, and even sterilization. The concentration of preservatives is high or the action time is long, and the purpose of disinfection can also be achieved. Disinfection and anti-corrosion drugs are harmful to human tissues and can only be used externally or for environmental disinfection.

(i) Chemical disinfectants

1. Types of chemical disinfectants

there are many types of chemical disinfectants, and their bactericidal effects are not the same. Generally available according to the characteristics of the use and disinfectant (see Table 4-2)

Table 4-2 Type, nature and use of disinfectants