13.1 Controlling Microbial Growth
3 min read•june 18, 2024
Controlling microbial growth is crucial in healthcare, food safety, and research. From household cleaners to high-tech methods, various approaches target different microbes. Understanding these techniques helps prevent infections and maintain sterile environments.
Biosafety levels guide lab practices for handling microbes. From for harmless bacteria to for deadly viruses, each level has specific protocols. These measures protect researchers and the public from potential biohazards.
Microbial Growth Control Methods
Disinfectants vs antiseptics vs sterilants
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- reduce microbial populations to safe levels on inanimate objects and surfaces (household cleaners, bleach, )
- prevent infection by reducing microbial populations on living tissue (hand sanitizers, , )
- eliminate all forms of microbial life, including spores, on inanimate objects ( gas, , )
Principles of sterilization and disinfection
- Physical methods
- Heat
- Moist heat: uses steam under pressure (121°C, 15 psi, 15-20 minutes)
- Dry heat: hot air oven employs higher temperatures and longer exposure times (160-180°C, 2-4 hours)
- removes microorganisms from liquids and gases using membrane filters with pore sizes 0.2-0.45 μm
- Radiation
- (gamma rays, X-rays) damages DNA
- () causes thymine dimers in DNA
- Heat
- Chemical methods
- Alcohols (, ) denature proteins and disrupt cell membranes, effective against vegetative bacteria, fungi, and enveloped viruses
- Halogens (, iodine) oxidize cellular components and denature proteins, effective against a wide range of microorganisms
- denature proteins and disrupt cell membranes, effective against vegetative bacteria and enveloped viruses
- Hydrogen peroxide and are strong oxidizing agents that damage cellular components, effective against a wide range of microorganisms, including spores
- Aldehydes (, glutaraldehyde) cross-link proteins and inactivate enzymes, effective against vegetative bacteria, fungi, and viruses
Antimicrobial Agents and Microbial Resistance
- are substances that kill or inhibit the growth of microorganisms
- Selective toxicity is the property of antimicrobial agents that allows them to harm microorganisms without significantly damaging host cells
- (MIC) is the lowest concentration of an antimicrobial agent that inhibits visible growth of a microorganism
- occurs when microorganisms develop mechanisms to survive exposure to antimicrobial agents, making treatments less effective
Biological Safety Levels and Handling Techniques
Biological safety levels and handling
- (BSL-1)
- Low-risk microorganisms not known to consistently cause disease in healthy adults (non-pathogenic E. coli, )
- Standard microbiological practices
- ()
- Moderate-risk microorganisms that can cause human disease (, Salmonella, )
- BSL-1 practices plus limited access to the lab, biohazard warning signs, sharps precautions, and a biosafety manual defining any needed waste decontamination or medical surveillance policies
- ()
- Indigenous or exotic microorganisms with potential for aerosol transmission and lethal disease (, , )
- BSL-2 practices plus controlled access, decontamination of all waste and lab clothing before laundering, and negative airflow into the laboratory
- (BSL-4)
- Dangerous and exotic microorganisms with a high risk of aerosol-transmitted infections, frequently fatal, or with no available vaccines or treatments (, , )
- BSL-3 practices plus clothing change before entering, shower on exit, and all material decontaminated on exit from the facility
- is crucial to prevent contamination and maintain sterile conditions
Key Terms to Review (88)
Antimicrobial Agents: Antimicrobial agents are substances that inhibit or destroy the growth and reproduction of microorganisms, such as bacteria, viruses, fungi, and parasites. These agents play a crucial role in controlling microbial growth and using chemicals to manage microorganisms in various contexts.
Antiseptic: An antiseptic is a chemical substance used to inhibit or eliminate microorganisms on living tissues, such as skin. It is essential in preventing infections during medical procedures.
Antiseptics: Antiseptics are chemical agents that inhibit or destroy the growth and development of microorganisms, particularly on living tissue. They are used to prevent infection and promote healing by reducing the risk of pathogenic microbial contamination in various medical and personal care applications.
Asepsis: Asepsis is the state of being free from disease-causing microorganisms. It involves practices and procedures to prevent infection.
Aseptic technique: Aseptic technique is a set of practices used to prevent contamination by pathogens and maintain sterility. It is crucial in microbiology, medical procedures, and laboratory experiments.
Aseptic Technique: Aseptic technique is a set of practices and procedures designed to prevent the introduction of microorganisms into a sterile environment, such as during medical procedures or scientific experiments. It is a crucial concept in the context of controlling microbial growth and understanding the historical debate surrounding spontaneous generation.
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: An autoclave is a pressurized chamber used to sterilize equipment and materials by exposing them to high-temperature steam under pressure. It is a crucial tool in microbiology and other scientific fields to ensure the elimination of microorganisms and the prevention of contamination.
Bacillus anthracis: Bacillus anthracis is a gram-positive, rod-shaped bacterium that causes anthrax. It is known for its ability to form resilient spores that can survive in harsh environments.
Bacillus subtilis: Bacillus subtilis is a Gram-positive, rod-shaped bacterium commonly found in soil and the gastrointestinal tract of ruminants. It is known for its ability to form a tough, protective endospore, allowing it to tolerate extreme environmental conditions.
Bactericide: A bactericide is a substance that kills bacteria. It is used in various settings to control the growth and spread of bacterial populations.
Biofilm: A biofilm is a complex aggregation of microorganisms growing on a surface, encased in a self-produced matrix of extracellular polymeric substances (EPS). These communities are highly resistant to antimicrobial agents and can be found in various environments, including medical devices and human tissues.
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.
Biological safety levels: Biological safety levels (BSLs) are a series of protections used to isolate dangerous biological agents in an enclosed laboratory facility. They range from BSL-1 to BSL-4, with increasing levels of containment and safety measures.
Biosafety Level 1: Biosafety Level 1 (BSL-1) is the basic level of biosafety precautions suitable for work with well-characterized agents that do not typically cause disease in healthy adult humans. It is the lowest level of containment and is commonly used in academic teaching laboratories and research facilities when working with microorganisms that pose minimal potential hazard.
Biosafety Level 2: Biosafety Level 2 (BSL-2) is a containment precaution level for handling biological agents or materials that pose a moderate risk to individuals and the community. It is designed to protect laboratory workers and the environment from potential exposure to pathogens that can cause human disease.
Biosafety Level 3: Biosafety Level 3 (BSL-3) is a containment precaution used in laboratories that handle infectious agents or potentially lethal biological materials. It is designed to minimize the risk of exposure and transmission of these hazardous substances to laboratory personnel and the general public.
Biosafety Level 4: Biosafety Level 4 (BSL-4) is the highest level of biosafety precautions, designed to handle the most dangerous and exotic microbiological agents that pose a high individual risk of life-threatening disease and for which no treatment or vaccine is available. This level of containment is crucial for controlling the growth and spread of such hazardous microorganisms.
Botulism: Botulism is a serious illness caused by the neurotoxin produced by Clostridium botulinum. It leads to muscle paralysis and can be life-threatening if not treated promptly.
BSL-1: BSL-1 (Biosafety Level 1) is the lowest level of biosafety precautions suitable for work involving well-characterized agents not known to cause disease in healthy adults. It involves standard microbiological practices without the need for special equipment or facilities.
BSL-2: BSL-2 (Biosafety Level 2) is a containment level for laboratories that handle moderate-risk microorganisms. It includes specific safety practices and equipment to prevent infection.
BSL-3: BSL-3 (Biosafety Level 3) is a containment protocol required for work involving microbes that can cause serious and potentially lethal diseases via inhalation. It includes strict laboratory practices, safety equipment, and facility design to prevent infection.
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.
BSLs: Biosafety Levels (BSLs) are standardized safety protocols used to contain infectious agents in laboratory settings. They range from BSL-1 to BSL-4, with increasing levels of containment and protection.
Catheters: Catheters are medical devices inserted into the body to drain fluids or administer treatments. They can become a site for microbial growth, potentially leading to infections.
Chlorine: Chlorine is a potent chemical disinfectant widely used to control microbial growth in water and on surfaces. It disrupts cellular processes, leading to the death of microorganisms.
Chlorine: Chlorine is a highly reactive chemical element that is commonly used as a disinfectant and antimicrobial agent. It is a key component in the control and management of microbial growth, as well as the use of chemicals to regulate and eliminate microorganisms.
Chlorine bleach: Chlorine bleach is a disinfectant and bleaching agent commonly used to kill bacteria, viruses, and fungi. It contains sodium hypochlorite as its active ingredient.
Clostridium botulinum: Clostridium botulinum is a Gram-positive, anaerobic bacterium known for producing the neurotoxin botulinum. This toxin causes botulism, a severe and potentially fatal illness.
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.
Critical item: A critical item is any device or instrument that penetrates sterile tissues, body cavities, or the vascular system and must be sterilized before use. These items pose a high risk for infection if contaminated.
D-value: D-value (decimal reduction time) is the time required at a specific temperature to reduce the microbial population by 90%. It is a critical parameter for evaluating the effectiveness of sterilization processes.
Decimal reduction time (DRT): Decimal reduction time (DRT) is the time required to reduce a microbial population by 90% at a specific temperature. It is a critical parameter in assessing the effectiveness of sterilization processes.
Degerming: Degerming is the mechanical removal of microbes from a limited area, such as skin around an injection site. It primarily involves physical means like scrubbing or using an antiseptic.
Disinfectant: A disinfectant is a chemical agent used to eliminate or reduce harmful microorganisms on inanimate objects and surfaces. It is crucial in preventing the spread of infections.
Disinfectants: Disinfectants are chemical agents that are used to destroy or inhibit the growth of harmful microorganisms, such as bacteria, viruses, and fungi, on inanimate surfaces or objects. They play a crucial role in controlling microbial growth and preventing the spread of infectious diseases in various settings, including healthcare facilities, food processing plants, and households.
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.
Ebola Virus: The Ebola virus is a highly contagious and often fatal viral infection that primarily affects humans and other primates. It is a member of the Filoviridae family, known for its unique filamentous shape and ability to cause severe hemorrhagic fever. The Ebola virus is a significant public health concern due to its high mortality rate and the potential for rapid spread in the absence of effective treatment or vaccine.
Endoscope: An endoscope is a medical device consisting of a long, thin, flexible or rigid tube with a light and camera used to examine the interior of a hollow organ or cavity. It is commonly used for minimally invasive diagnostic and therapeutic procedures.
Endospore: An endospore is a tough, dormant, and non-reproductive structure produced by certain bacteria to ensure survival in harsh conditions. It is highly resistant to extreme temperatures, desiccation, chemicals, and radiation.
Escherichia coli: Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacterium commonly found in the intestines of warm-blooded organisms. While most strains are harmless, some can cause serious food poisoning and infections.
Ethanol: Ethanol, also known as ethyl alcohol or grain alcohol, is a colorless, volatile, flammable liquid that is the primary type of alcohol found in alcoholic beverages. It is produced through the fermentation of sugars by yeast and has a wide range of applications, from being a fuel source to a disinfectant and preservative.
Ethanol is closely tied to the topics of 1.1 What Our Ancestors Knew, 8.2 Catabolism of Carbohydrates, 8.4 Fermentation, 13.1 Controlling Microbial Growth, and 13.3 Using Chemicals to Control Microorganisms. Its production, properties, and uses are integral to understanding these key concepts in microbiology.
Ethylene Oxide: Ethylene oxide is a highly reactive, flammable gas that is widely used as a sterilizing agent for medical equipment and devices. It is a key chemical in the context of controlling microbial growth, as it is an effective disinfectant and sterilant against a broad spectrum of microorganisms.
Filtration: Filtration is a physical separation process that removes particulate matter from a fluid by passing it through a porous medium. It is a crucial technique used in various contexts, including the control of microbial growth, to purify and sterilize liquids and gases.
Fomite: A fomite is any inanimate object or material that can carry and transfer pathogens, contributing to the spread of infectious diseases. Common examples include doorknobs, utensils, and medical instruments.
Formaldehyde: Formaldehyde is a colorless, flammable gas with a pungent odor that is widely used in various industries and medical applications. It is a key term in the context of controlling microbial growth, as it is a powerful disinfectant and sterilizing agent.
Francisella tularensis: Francisella tularensis is a highly infectious bacterium that causes the disease tularemia, also known as 'rabbit fever'. It is primarily transmitted through contact with infected animals, contaminated food or water, or the bite of infected ticks or other insects. Francisella tularensis is considered a potential bioterrorism agent due to its ability to cause severe illness and its potential for weaponization.
Fungicide: A fungicide is a chemical compound or biological organism used to kill or inhibit the growth of fungi. It is commonly used in agriculture and medicine to control fungal infections.
Fungistatic: Fungistatic agents inhibit the growth and reproduction of fungi without killing them. They are often used to control fungal infections in various environments.
Glutaraldehyde: Glutaraldehyde is a strong disinfectant and sterilizing agent commonly used in medical and laboratory settings to control the growth of microorganisms. It is a versatile chemical that can effectively kill a wide range of bacteria, viruses, fungi, and spores, making it an important tool in the context of controlling microbial growth.
Gram’s iodine: Gram's iodine is a mordant used during the Gram staining procedure. It forms a complex with crystal violet dye, enhancing its retention in bacterial cell walls.
Handwashing: Handwashing is the process of cleaning hands with soap and water to remove dirt, germs, and microorganisms. It is a fundamental practice in preventing the spread of infectious diseases.
Hepatitis B Virus: The hepatitis B virus (HBV) is a highly contagious DNA virus that primarily infects the liver, causing inflammation and potential long-term liver damage. It is a significant global health concern, as chronic HBV infection can lead to cirrhosis and liver cancer if left untreated.
HIV: HIV (Human Immunodeficiency Virus) is a virus that targets the immune system, specifically CD4 cells (T cells), leading to a progressive failure of the immune system. If left untreated, HIV can lead to AIDS (Acquired Immunodeficiency Syndrome).
Hydrogen peroxide: Hydrogen peroxide (H2O2) is a chemical compound often used as a disinfectant and antiseptic. It is also a byproduct of certain metabolic pathways in microorganisms.
Hydrogen Peroxide: Hydrogen peroxide (H2O2) is a chemical compound consisting of two hydrogen atoms and two oxygen atoms. It is a colorless liquid with strong oxidizing properties, making it a useful antimicrobial agent in the context of controlling microbial growth and using chemicals to control microorganisms.
Iodine: Iodine is a chemical element that is essential for the proper functioning of the thyroid gland, which regulates metabolism and other important bodily processes. It is a key component in the production of thyroid hormones and plays a crucial role in controlling microbial growth and using chemicals to control microorganisms.
Ionizing Radiation: Ionizing radiation refers to high-energy electromagnetic waves or particles that have enough energy to remove electrons from atoms or molecules, creating charged particles called ions. This process is particularly relevant in the context of controlling microbial growth, as ionizing radiation can be used to inactivate or kill microorganisms.
Isopropanol: Isopropanol, also known as isopropyl alcohol or 2-propanol, is a chemical compound commonly used as a disinfectant, solvent, and antiseptic. It is particularly relevant in the context of controlling microbial growth and using chemicals to manage microorganisms.
Isopropyl alcohol: Isopropyl alcohol, also known as isopropanol, is a colorless, flammable liquid with antiseptic properties used to disinfect surfaces and instruments. It works by denaturing proteins and dissolving lipids, effectively killing or inhibiting microbial growth.
Lassa virus: Lassa virus is a member of the Arenaviridae family and is the causative agent of Lassa fever, a severe and potentially life-threatening viral hemorrhagic fever. It is primarily transmitted to humans through contact with infected rodents or their excreta, making it an important public health concern in endemic areas.
Marburg Virus: The Marburg virus is a highly infectious and deadly virus that causes a severe and often fatal hemorrhagic fever. It is a member of the Filoviridae family, which also includes the Ebola virus. The Marburg virus is considered a significant public health concern due to its high mortality rate and potential for rapid transmission.
Microbial death curve: A microbial death curve is a graphical representation that shows the decline in the number of viable microorganisms over time when exposed to a lethal agent. It typically plots logarithmic reduction versus time.
Microbial Resistance: Microbial resistance refers to the ability of microorganisms, such as bacteria, viruses, and fungi, to withstand and survive the effects of antimicrobial agents, including antibiotics, disinfectants, and other control measures. This concept is crucial in understanding how to effectively control and manage microbial growth in various contexts, including healthcare, food production, and the environment.
Minimum Inhibitory Concentration: The minimum inhibitory concentration (MIC) is the lowest concentration of an antimicrobial agent that is required to inhibit the visible growth of a microorganism under defined in vitro conditions. It is a crucial parameter in understanding the effectiveness of antimicrobial agents and their potential for controlling microbial growth in various contexts, such as infection treatment, disinfection, and assessing drug resistance.
Mycobacterium tuberculosis: Mycobacterium tuberculosis is a pathogenic bacterial species in the Mycobacteriaceae family, responsible for causing tuberculosis (TB). It primarily affects the lungs but can also infect other parts of the body.
Non-Ionizing Radiation: Non-ionizing radiation refers to a type of electromagnetic radiation that does not have enough energy to ionize atoms or molecules, meaning it cannot directly break chemical bonds or remove electrons from atoms. This type of radiation is lower in energy compared to ionizing radiation and includes visible light, infrared, and radio waves, among others.
Noncritical item: A noncritical item is a medical or laboratory instrument that contacts intact skin but does not penetrate it. These items pose a low risk of infection transmission.
Peracetic acid: Peracetic acid is a potent oxidizing agent used as a disinfectant and sterilant. It is effective against a broad spectrum of microorganisms including bacteria, viruses, fungi, and spores.
Peracetic Acid: Peracetic acid is a powerful oxidizing agent that is commonly used as a disinfectant and sanitizer in various industries, including healthcare, food processing, and water treatment. It is an effective antimicrobial agent that can kill a wide range of microorganisms, including bacteria, viruses, and fungi.
Phenolics: Phenolics are a class of chemical compounds commonly used as disinfectants due to their ability to denature proteins and disrupt cell membranes. They are effective against a wide range of microorganisms including bacteria, fungi, and viruses.
Phenolics: Phenolics are a class of organic compounds containing one or more hydroxyl (-OH) groups attached to an aromatic hydrocarbon ring. They are widely found in plants and play important roles in controlling microbial growth and as chemical agents to inhibit microorganisms.
Sanitization: Sanitization is the process of reducing microbial populations to levels that are considered safe by public health standards. It does not necessarily eliminate all microorganisms but aims to lower the risk of spreading infection.
SARS-CoV: SARS-CoV, or Severe Acute Respiratory Syndrome Coronavirus, is the virus that causes the respiratory illness known as SARS. It is a type of coronavirus that can be transmitted from animals to humans and has the potential to cause severe illness and global outbreaks.
Semicritical item: A semicritical item is a medical device that comes into contact with mucous membranes or non-intact skin. These items require high-level disinfection but not necessarily sterilization.
Sepsis: Sepsis is a life-threatening condition caused by the body's extreme response to an infection, leading to tissue damage, organ failure, and potentially death. It occurs when chemicals released into the bloodstream to fight an infection trigger widespread inflammation.
Staphylococcus aureus: Staphylococcus aureus is a Gram-positive bacterium commonly found on the skin and in the nasal passages. It can cause a range of infections from minor skin conditions to severe diseases like pneumonia and sepsis.
Sterilant: A sterilant is a chemical agent capable of completely eliminating all forms of microbial life, including bacteria, viruses, fungi, and spores. It is used to achieve sterilization in medical and laboratory settings.
Sterilants: Sterilants are chemical agents or physical processes used to eliminate all forms of microbial life, including vegetative cells, spores, and viruses, from inanimate surfaces, equipment, and medical devices. They are employed to achieve a state of sterility, which is the complete absence of any living microorganisms.
Sterile field: A sterile field is an area free of microorganisms, created by using sterilized materials and techniques to prevent contamination during medical procedures. It is essential for maintaining asepsis in environments where controlling microbial growth is crucial.
Sterilization: Sterilization is the process of eliminating all forms of microbial life, including bacteria, viruses, fungi, and spores. It is a critical procedure in various fields to ensure complete microbial control.
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.
Urinary tract infection: A urinary tract infection (UTI) is an infection in any part of the urinary system, including kidneys, bladder, ureters, and urethra. Most infections involve the lower urinary tract and are commonly caused by bacteria.
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.
Vinegar: Vinegar is an acidic liquid produced through the fermentation of ethanol by acetic acid bacteria. Its acidic nature makes it useful for controlling microbial growth.
Viricide: A viricide is an agent that deactivates or destroys viruses, thereby inhibiting their ability to replicate and cause infection. Viricides are used in various settings to control viral contamination and transmission.