13.2 Using Physical Methods to Control Microorganisms
3 min read•june 18, 2024
Heat, , and physical methods are powerful tools for controlling microbes. From to , these techniques kill or inhibit microorganisms in various settings. Understanding their applications is crucial for food safety, medical , and lab work.
Filtration and radiation offer additional ways to remove or inactivate microbes. These methods are vital in healthcare, food processing, and research. Knowing the differences between sterilization, , and other control terms helps ensure proper microbial management in different contexts.
Heat-Based Methods for Controlling Microbial Growth
Heat-based microbial control methods
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- heats liquids to 63-72°C for 30 minutes or 72-75°C for 15 seconds, killing most (Salmonella), some viruses, and some fungi but not ; used for milk, beer, and other liquids
- heats materials to 121°C at 15 psi for 15-20 minutes, killing all microbes including endospores (Clostridium); used for sterilizing laboratory media, instruments (petri dishes), and medical devices
- heats liquids to 100°C at sea level, killing most vegetative bacteria (E. coli) and some viruses but not endospores or some heat-resistant viruses; used for disinfecting drinking water and surgical instruments (scalpels)
- is the time required to kill all microorganisms in a sample at a specific temperature
Physical Methods for Inhibiting Microbial Growth
Physical inhibition of microbial growth
- removes moisture from a material, inhibiting microbial growth by limiting water availability; used for preserving foods such as dried meats (beef jerky), fruits (raisins), and grains (rice)
- lowers temperature below 0°C, inhibiting microbial growth by slowing metabolic processes and limiting water availability; used for preserving foods such as frozen vegetables (peas), meats (chicken), and ice cream
- applies pressures of 100-1000 MPa, inactivating microbes by disrupting cell membranes and denaturing proteins; used for preserving foods such as guacamole, salsa, and oysters
- (freeze-drying) removes water from frozen materials, preserving microorganisms and biological materials for long-term storage
Radiation and Filtration for Sterilization and Disinfection
Radiation and filtration for sterilization
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Radiation
- ( and ) damages DNA and other cellular components; used for sterilizing medical devices (syringes), pharmaceuticals, and food packaging
- Non-ionizing radiation () damages DNA and proteins; used for disinfecting surfaces, air, and water in laboratories and healthcare settings (hospitals)
- , a form of ionized gas, can inactivate microorganisms on surfaces and in liquids
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Filtration removes microbes from a liquid or gas by passing through a filter with small pores
- with 0.2-0.45 μm pores remove most bacteria (Pseudomonas), protozoa, and fungi; used for sterilizing heat-sensitive solutions (antibiotics) and air in laboratories and industry (pharmaceuticals)
- with 0.3 μm pores remove 99.97% of particles 0.3 μm, including most bacteria and some viruses (influenza); used for sterilizing air in clean rooms, operating rooms, and biosafety cabinets
Microbial Control Terminology
- Sterilization: The complete elimination of all living microorganisms, including bacterial endospores
- : The elimination of most pathogenic microorganisms, but not necessarily all microbial forms (e.g., bacterial endospores)
- : The time required to kill 90% of the microorganisms in a sample at a specific temperature
Key Terms to Review (73)
Autoclave: An autoclave is a device that uses steam under high pressure to sterilize equipment and materials. It is commonly used in microbiology labs to eliminate all forms of microbial life, including spores.
Autoclave tape: Autoclave tape is a specialized adhesive tape used to indicate whether items have been correctly sterilized in an autoclave. It changes color when exposed to specific temperatures and pressures.
Autoclaving: Autoclaving is a sterilization method that uses high-pressure saturated steam at 121°C for typically 15-20 minutes to eliminate all forms of microbial life, including spores. It is commonly used in laboratories and medical settings to sterilize equipment and media.
Autoclaving: Autoclaving is a sterilization method that uses high-pressure steam to kill microorganisms, including spores, through the application of moist heat. This process is commonly used in laboratories, healthcare facilities, and industrial settings to ensure the sterility of equipment, materials, and solutions.
Biological indicator spore tests: Biological indicator spore tests are used to validate the efficacy of sterilization processes by using highly resistant bacterial spores. If these spores are successfully killed, it indicates that the sterilization process is effective.
Biological safety cabinet: A biological safety cabinet (BSC) is an enclosed, ventilated laboratory workspace designed to protect the user, experimental material, and the environment from biohazards and contamination. It uses high-efficiency particulate air (HEPA) filters to clean the air that flows in and out of the cabinet.
Boiling: Boiling is the process of heating a liquid to its boiling point, causing it to vaporize. In microbiology, it is used to kill microorganisms by denaturing their proteins and disrupting cell membranes.
Boiling: Boiling is the process of heating a liquid to the point where bubbles of vapor form and rise to the surface, indicating the liquid has reached its boiling point. This phase change from liquid to gas is a key physical method used to control microorganisms.
BSL-4: BSL-4 (Biosafety Level 4) is the highest level of biological safety containment. It is used for work with highly dangerous and exotic pathogens that pose a high risk of aerosol-transmitted infections and for which there are no available vaccines or treatments.
Canning: Canning is a method of preserving food where it is processed and sealed in an airtight container to inhibit microbial growth. The process involves heating to destroy microorganisms and enzymes that could cause spoilage.
Cavitation: Cavitation is the formation and collapse of vapor-filled bubbles in a liquid, which can result in localized high temperatures and pressures. In microbiology, this phenomenon is often used for the mechanical disruption of cells.
Chamberland: Chamberland is a type of porcelain filter invented by Charles Chamberland in 1884. It is used to remove bacteria from liquids, making it crucial for studying viruses and controlling microbial growth.
Clostridium perfringens: Clostridium perfringens is a Gram-positive, anaerobic, spore-forming bacterium commonly found in soil, decaying vegetation, and the intestines of humans and animals. It is known for causing gas gangrene and food poisoning.
Cold Plasma: Cold plasma, also known as non-thermal plasma, is a partially ionized gas that is generated at relatively low temperatures, typically below 100°C. Unlike the high-temperature plasma found in stars or fusion reactors, cold plasma can be generated and manipulated at normal atmospheric conditions, making it a versatile tool for various applications, including the control of microorganisms.
Commercial sterilization: Commercial sterilization is a process that uses heat to destroy all microorganisms in food products, ensuring they are safe for consumption. It aims specifically to eliminate Clostridium botulinum spores to prevent botulism.
Decimal Reduction Time: Decimal reduction time, also known as D-value, is a measure of the time required to inactivate or kill 90% of a microbial population under specific environmental conditions. It is a critical parameter in understanding the effectiveness of physical methods used to control microorganisms, such as heat, radiation, and chemical treatments.
Desiccation: Desiccation is the process of removing water from microorganisms, leading to their inhibition or death. It is a physical method used to control microbial growth by depriving cells of the moisture necessary for metabolic processes.
Desiccation: Desiccation refers to the process of extreme drying or dehydration, where an organism or material loses a significant amount of its water content. This term is particularly relevant in the context of lichens and physical methods for controlling microorganisms.
Diack tube: A Diack tube is a device used to monitor the effectiveness of sterilization processes. It contains heat-sensitive chemicals that change color when exposed to specific temperatures.
Disinfection: Disinfection is the process of eliminating or reducing harmful microorganisms from inanimate objects and surfaces. It does not necessarily kill all microorganisms, especially resistant bacterial spores.
Disinfection: Disinfection is the process of eliminating or inactivating pathogenic microorganisms, such as bacteria, viruses, and fungi, from inanimate objects or surfaces. It is a crucial step in controlling microbial growth and preventing the spread of infectious diseases.
Dry ice: Dry ice is the solid form of carbon dioxide (CO2), commonly used as a cooling agent. It sublimates at -78.5°C (-109.3°F) and is useful in various industrial and scientific applications.
Dry-heat sterilization: Dry-heat sterilization uses high temperatures to kill microorganisms, typically through hot air ovens. This method is effective for materials that can withstand high heat and are not suitable for moist-heat sterilization.
Endospores: Endospores are specialized, dormant structures formed by certain Gram-positive bacteria, such as Bacillus and Clostridium species, in response to environmental stressors. These resilient structures allow the bacteria to survive harsh conditions and remain viable for extended periods, even in the absence of nutrients or water.
Food preservation: Food preservation is the process of treating and handling food to stop or slow down spoilage, loss of quality, edibility, or nutritional value. It often involves controlling the growth of microorganisms such as bacteria, fungi, and yeasts.
Freezing: Freezing is a physical method used to control microorganisms by exposing them to temperatures below the freezing point of water, typically at or below 32°F (0°C). This process disrupts the cellular structure and function of microbial cells, leading to their inactivation or death.
Gamma irradiation: Gamma irradiation is a process that uses high-energy gamma rays to kill or inactivate microorganisms. It is often used for sterilization and decontamination in various fields, including medical equipment and food safety.
Gamma rays: Gamma rays are high-frequency electromagnetic waves with the shortest wavelength and highest energy in the electromagnetic spectrum. They can cause mutations in DNA and are used for sterilizing medical equipment.
Gamma Rays: Gamma rays are a type of high-energy electromagnetic radiation, similar to X-rays, that are produced by the radioactive decay of atomic nuclei. They have the highest frequency and shortest wavelength within the electromagnetic spectrum, making them highly penetrating and capable of causing significant damage to living tissues.
Gas gangrene: Gas gangrene is a severe bacterial infection that produces gas within tissues. It is typically caused by Clostridium species, especially Clostridium perfringens.
Geobacillus stearothermophilus: Geobacillus stearothermophilus is a thermophilic bacterium commonly used as a biological indicator for sterilization processes. It is highly resistant to heat and can survive at temperatures up to 75°C.
Gravity displacement autoclave: A gravity displacement autoclave is a type of steam sterilizer that removes air through gravity, allowing steam to displace the air and effectively sterilize medical and laboratory equipment. It operates at high temperatures and pressures to kill all forms of microbial life, including spores.
Gray: Gray refers to the intermediate or neutral color between black and white, often associated with a sense of neutrality, balance, and lack of strong contrast or distinction. In the context of using physical methods to control microorganisms, the term 'gray' can be used to describe certain aspects of these processes.
HEPA Filters: HEPA (High-Efficiency Particulate Air) filters are a type of air filtration system designed to remove a high percentage of small airborne particles, including microbes, from the air. These filters are widely used in various settings, including hospitals, laboratories, and industrial facilities, to maintain clean and sterile environments.
High Pressure: High pressure refers to the application of elevated atmospheric or hydrostatic pressure as a physical method to control and inactivate microorganisms. This technique is commonly used in the food industry to enhance food safety and extend shelf life by killing pathogenic and spoilage microbes without the need for thermal processing or chemical additives.
High-efficiency particulate air (HEPA) filter: A high-efficiency particulate air (HEPA) filter is a type of air filter that can remove at least 99.97% of airborne particles as small as 0.3 micrometers. HEPA filters are crucial for maintaining sterile environments by trapping microorganisms and other contaminants.
High-pressure processing: High-pressure processing (HPP) is a method used to preserve and sterilize food by applying high levels of hydrostatic pressure. This process inactivates microorganisms without the need for heat, maintaining food quality.
High-temperature short-time (HTST) pasteurization: High-temperature short-time (HTST) pasteurization is a method used to kill pathogenic microorganisms in liquid foods by heating them to a specific temperature for a short period. It is widely used in the dairy industry to ensure the safety and extend the shelf life of milk.
Hyperbaric oxygen therapy: Hyperbaric oxygen therapy (HBOT) is a medical treatment that involves breathing pure oxygen in a pressurized room or chamber. It is used to enhance the body's natural healing processes and combat certain types of infections.
Ionizing radiation: Ionizing radiation is a type of energy released by atoms that travels in the form of electromagnetic waves or particles. It has enough energy to remove tightly bound electrons from atoms, creating ions.
Liquid nitrogen: Liquid nitrogen is nitrogen in a liquid state at an extremely low temperature, commonly used for rapid freezing and cryopreservation.
Lyophilization: Lyophilization, also known as freeze-drying, is a dehydration process used to preserve perishable materials by freezing them and then reducing the surrounding pressure to allow the frozen water to sublimate directly from the solid phase to the gas phase. This technique is widely used in microbiology for preserving microbial cultures.
Lyophilization: Lyophilization, also known as freeze-drying, is a dehydration process that removes water from a substance through the use of sublimation. This technique is commonly employed in the preservation and storage of various materials, including pharmaceuticals, biological samples, and food products.
Membrane Filters: Membrane filters are porous, thin sheets made of various materials that are used to physically separate and remove microorganisms, particles, and other contaminants from liquids or gases. They are a crucial tool in controlling microorganisms through physical methods as described in the chapter on Using Physical Methods to Control Microorganisms.
Membrane filtration: Membrane filtration is a physical method used to remove microorganisms from liquids by passing them through a filter with pores small enough to retain bacteria and other microbes. This technique is essential for sterilizing heat-sensitive solutions and for microbial analysis.
Moist-heat sterilization: Moist-heat sterilization is a method of killing microorganisms using steam under pressure. It is commonly used in autoclaves to achieve high temperatures that denature microbial proteins and destroy all forms of microbial life, including spores.
Nonionizing radiation: Nonionizing radiation is a type of electromagnetic radiation that does not carry enough energy to ionize atoms or molecules. It can affect the structure and function of DNA, causing mutations or microbial control without breaking chemical bonds.
Pascal: Pascal is a unit of pressure measurement in the International System of Units (SI). It is defined as the force of one newton exerted over an area of one square meter, and is commonly used to quantify the pressure exerted by physical methods used to control microorganisms.
Pascalization: Pascalization is a method of preserving and sterilizing food by applying high hydrostatic pressure. This process inactivates microorganisms, enzymes, and spores without the use of heat.
Pasteur: Louis Pasteur was a pioneering French microbiologist and chemist renowned for his discoveries in the principles of vaccination, microbial fermentation, and pasteurization. His work laid the foundation for modern microbiology and helped disprove the theory of spontaneous generation.
Pasteurization: Pasteurization is a heat treatment process that kills pathogenic microorganisms in foods and beverages. It aims to extend shelf life while maintaining the nutritional and sensory qualities.
Pasteurization: Pasteurization is a process that involves the controlled application of heat to food or beverage products to kill harmful microorganisms, such as bacteria, viruses, and parasites, without significantly altering the product's nutritional value or taste. This process is named after the French scientist Louis Pasteur, who pioneered the technique in the 19th century.
Pasteurization plays a crucial role in ensuring the safety and extending the shelf life of a wide range of food and beverage products, from dairy items like milk and cheese to juices, wines, and other consumables. By eliminating potentially harmful microbes, pasteurization helps prevent the spread of foodborne illnesses and enhances the overall quality and stability of the final product.
Prevacuum sterilizer: A prevacuum sterilizer is a type of autoclave that uses a vacuum pump to remove air from the chamber before steam is introduced. This ensures more effective penetration of steam for sterilization.
Psychrophiles: Psychrophiles are microorganisms that thrive in extremely cold environments, typically at temperatures of 0°C to 15°C. They play a crucial role in nutrient cycling in polar regions and deep ocean waters.
Radiation: Radiation is the emission of energy as electromagnetic waves or as moving subatomic particles, which can be used to control microbial growth. It can damage the DNA and cellular structures of microorganisms, leading to their inactivation or death.
Refrigeration: Refrigeration is the process of lowering the temperature of an environment or substance to slow down microbial growth. It is commonly used for preserving food and biological samples.
Retort: A retort is a vessel used for sterilization by applying high-temperature steam under pressure. It is commonly utilized in the food and beverage industry to ensure microbial control.
Sonication: Sonication is the use of high-frequency sound waves to disrupt cell structures. It is commonly used in microbiology for lysing cells and reducing microbial load.
Sterilization: Sterilization is the process of eliminating or destroying all forms of microbial life, including vegetative cells and spores, to achieve a state of absolute sterility. This term is crucial in the context of controlling microbial growth, using physical methods to control microorganisms, and utilizing chemicals to control microorganisms.
Syringe filter: A syringe filter is a single-use, membrane-based device attached to the end of a syringe to remove particles from liquid samples before analysis. It ensures sterility and clarity in microbiological experiments.
Thermal death point (TDP): The thermal death point (TDP) is the lowest temperature at which all microorganisms in a liquid suspension are killed in 10 minutes. It is an important parameter for determining the effectiveness of heat sterilization methods.
Thermal Death Time: Thermal death time (TDT) is a measure of the heat resistance of microorganisms. It refers to the minimum time required to kill a specific number of microorganisms at a given temperature. TDT is a crucial concept in understanding the effects of temperature on microbial growth and the use of physical methods to control microorganisms.
Thermal death time (TDT): Thermal Death Time (TDT) is the shortest time required to kill all microorganisms in a liquid suspension at a specific temperature. It is a critical parameter in sterilization processes.
Thymine dimer: A thymine dimer is a type of DNA damage caused by ultraviolet (UV) radiation in which two adjacent thymine bases bond together, disrupting normal DNA structure. This can lead to mutations if not repaired.
Ultra-high-temperature (UHT) pasteurization: Ultra-high-temperature (UHT) pasteurization is a food processing technology that sterilizes liquid food by heating it above 135°C for 2 to 5 seconds. This method extends shelf life without refrigeration and kills most microorganisms.
Ultra-low freezer: An ultra-low freezer is a specialized refrigeration unit designed to store biological samples at extremely low temperatures, typically between -50°C and -80°C. It helps preserve the integrity of microorganisms and prevent their growth.
UV light: UV light is a form of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays. It is commonly used in microbiology to control microbial growth by damaging the DNA of microorganisms.
UV Light: UV (ultraviolet) light is a type of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays. It is a physical method used to control and kill microorganisms due to its ability to damage their genetic material and disrupt cellular processes.
Vacuum filter: A vacuum filter is a device used to separate particles from liquids or gases by using a vacuum to pull the fluid through a filtration membrane. It is commonly used to sterilize solutions by removing microorganisms.
Vegetative Bacteria: Vegetative bacteria refer to the active, growing, and reproducing form of bacterial cells. These bacteria are metabolically active, carrying out various cellular processes to support their growth and proliferation. Vegetative bacteria are the predominant form found in most environments and are the focus of physical control methods discussed in the chapter on Using Physical Methods to Control Microorganisms.
Water activity: Water activity (a_w) measures the availability of water in a substance for microbial growth. It ranges from 0 (completely dry) to 1 (pure water).
Water purification: Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is safe for specific uses, such as drinking or laboratory work.
X-rays: X-rays are a form of electromagnetic radiation with high energy and short wavelengths. They are capable of penetrating most substances, making them useful in medical imaging and microbial studies.