Prescott's Microbiology - Control of Microorganisms PDF

Prescott’s MICROBIOLOGY ELEVENTH EDITION JOANNE WILLEY KATHLEEN SANDMAN DOROTHY WOOD Control of Microorganisms in the Environment  Microbial Characteristics and Microbial Control Figure 7.11 2 ©2020 McGraw-Hil...

Prescott’s MICROBIOLOGY ELEVENTH EDITION JOANNE WILLEY KATHLEEN SANDMAN DOROTHY WOOD Control of Microorganisms in the Environment  Microbial Characteristics and Microbial Control Figure 7.11 2 ©2020 McGraw-Hill Education  Common Microbial Control Methods Disinfection: The destruction or removal of vegetative pathogens but not bacterial endospores. Usually used only on inanimate objects. Sterilization: The complete removal or destruction of all viable microorganisms. Used on inanimate objects. Antisepsis: Chemicals applied to body surface to destroy or inhibit vegetative pathogens. Chemotherapy: Chemicals used internally to kill or inhibit growth of microorganisms within host tissues. Access the text alternative for these images 3 ©2020 McGraw-Hill Education  Definition of Frequently Used Terms Sterilization. Destruction or removal of all viable organisms. Disinfection. Killing, inhibition, or removal of disease causing (pathogenic) organisms. Disinfectants—agents, usually chemical, used for disinfection, usually used on inanimate objects. Sanitization. Reduction of microbial population to levels deemed safe (based on public health standards). Antisepsis. Prevention of infection of living tissue by microorganisms. Antiseptics—chemical agents that kill or inhibit growth of microorganisms when applied to tissue. 4 ©2020 McGraw-Hill Education  Impact of Biocide Exposure Access the text alternative for these images 5 ©2020 McGraw-Hill Education  Antimicrobial Agents Chemotherapy. Use of chemicals to kill or inhibit growth of microorganisms within host tissue. Cidal agents kill (-cide suffix indicates agent that kills). Include bactericides, fungicides, and viricides. Static agents inhibit growth (-static suffix indicates growth inhibiting agent). Include bacteriostatic and fungistatic. 6 ©2020 McGraw-Hill Education  The Pattern of Microbial Death Microorganisms are not killed instantly. Population death usually occurs exponentially. Measure of agent’s killing efficiency. Decimal reduction time—time to kill 90%. Must be sure viable but nonculturable cells are dead. Once they recover, they may regain the ability to reproduce and cause infection. 7 ©2020 McGraw-Hill Education  Actions of Microbial Control Agents Alternation of membrane permeability Damage to proteins Damage to nucleic acids 8 ©2020 McGraw-Hill Education  Filtration Reduces microbial population or sterilizes solutions of heat-sensitive materials by removing microorganisms. Also used to reduce microbial populations in air. 9 ©2020 McGraw-Hill Education  Filtering Liquids Membrane filters. Porous membranes with defined pore sizes that remove microorganisms primarily by physical screening. Access the text alternative for these images 10 ©2020 McGraw-Hill Education  Filtering Air Surgical masks. High-efficiency particulate air (HEPA) filters. Used in laminar flow biological safety cabinets. Access the text alternative for these images 11 ©2020 McGraw-Hill Education  Moist Heat Destroys viruses, fungi, and bacteria. Boiling will not destroy endospores and does not sterilize. Degrades nucleic acids, denatures proteins, and disrupts membranes. Entity Vegetative Cells Spores Yeasts 5 minutes at 50– 5 minutes at 70–80°C 60°C Molds 30 minutes at 62°C 30 minutes at 80°C Mesophilic 10 minutes at 60– 2 to over 800 minutes at 100°C Bacteria 70°C 0.5–12 minutes at 121°C Viruses 30 minutes at 60°C Prions 90 minutes at 134°C 12 ©2020 McGraw-Hill Education  Steam Sterilization Carried out above 100oC which requires saturated steam under pressure. Uses an autoclave. Effective against all types of microorganisms (including spores!). Quality control—includes strips with Geobacillus stearothermophilus. Access the text alternative for these images 13 ©2020 McGraw-Hill Education  Pasteurization Controlled heating at temperatures well below boiling. Used for milk, beer, and other beverages. Process does not sterilize but does kill pathogens present and slow spoilage by reducing the total load of organisms present. 14 ©2020 McGraw-Hill Education  Dry Heat Sterilization Less effective than moist heat sterilization, requiring higher temperatures and longer exposure times. Items subjected to 160 to 170oC for 2 to 3 hours. Oxidizes cell constituents and denatures proteins. Does not corrode glassware and metal instruments as moist heat does. 15 ©2020 McGraw-Hill Education  Dry Heat Incineration Bench top incinerators are used to sterilize inoculating loops used in microbiology laboratories. 16 ©2020 McGraw-Hill Education  Ultraviolet (UV) Radiation Wavelength of 260 is most bactericidal (DNA absorbs). Causes thymine dimers preventing replication and transcription. UV limited to surface sterilization because it does not penetrate glass, dirt films, water, and other substances. Has been used for water treatment. 17 ©2020 McGraw-Hill Education  Ionizing Radiation Gamma radiation penetrates deep into objects. Destroys bacterial endospores; not always effective against viruses. Used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies, and food. Access the text alternative for these images 18 ©2020 McGraw-Hill Education  Chemical Control Agents and Their Requirements Disinfection. Ideally is effective against wide variety of infectious agents at low concentrations and in the presence of organic matter. Antisepsis. Overuse of antiseptics such as triclosan has selected for triclosan-resistant bacteria. Sterilization. 19 ©2020 McGraw-Hill Education  Phenolics Commonly used as laboratory and hospital disinfectants. Act by denaturing proteins and disrupting cell membranes. Tuberculocidal, effective in presence of organic material, and long lasting. Disagreeable odor and can cause skin irritation. 20 ©2020 McGraw-Hill Education  Alcohols Among the most widely used disinfectants, antiseptics, and sanitizers. Two most common are ethanol and isopropanol. Bactericidal, fungicidal, but not sporicidal. Inactivate some viruses. Denature proteins and possibly dissolve membrane lipids. 21 ©2020 McGraw-Hill Education  Halogens—Iodine Skin antiseptic. Oxidizes cell constituents and iodinates proteins. At high concentrations may kill endospores. Skin damage, staining, and allergies can be a problem. Iodophor. Iodine complexed with organic carrier. Released slowly to minimize skin burns. 22 ©2020 McGraw-Hill Education  Halogens—Chlorine Oxidizes cell constituents. Important in disinfection of water supplies and swimming pools, used in dairy and food industries, effective household disinfectant. Destroys vegetative bacteria and fungi. Chlorine gas is sporicidal. 23 ©2020 McGraw-Hill Education  Heavy Metals For example, ions of mercury, silver, arsenic, zinc, and copper. Effective but usually toxic. Combine with and inactivate proteins; may also precipitate cell proteins. 24 ©2020 McGraw-Hill Education  Quaternary Ammonium Compounds Detergents that have broad spectrum antimicrobial activity and are effective disinfectants. Amphipathic organic cleansing agents. Cationic detergents are effective disinfectants. Kill most bacteria, but not M. tuberculosis or endospores. Stable and nontoxic, inactivated by hard water and soap. 25 ©2020 McGraw-Hill Education  Aldehydes Commonly used agents are formaldehyde and glutaraldehyde. Highly reactive molecules. Sporicidal and can be used as chemical sterilants. 26 ©2020 McGraw-Hill Education  Effects of Glutaraldehyde Access the text alternative for these images 27 ©2020 McGraw-Hill Education  Sterilizing Gases Used to sterilize heat- sensitive materials. Microbicidal and sporicidal. Ethylene oxide sterilization is carried out in equipment resembling an autoclave. Vaporized hydrogen peroxide can also be used. Access the text alternative for these images 28 ©2020 McGraw-Hill Education  Chemical Methods of Microbial Control Evaluating a disinfectant Disk-diffusion method Figure 7.6 29 ©2020 McGraw-Hill Education  Evaluation of Antimicrobial Agent Effectiveness Complex process regulated by U.S. federal agencies: Environmental Protection Agency regulates disinfectants. Food and Drug Administration regulates agents used on humans and animals. 30 ©2020 McGraw-Hill Education Conditions Influencing the Effectiveness of Antimicrobial Agent Activity 1 Population size. Larger populations take longer to kill than smaller populations. Population composition. Microorganisms differ markedly in their sensitivity to antimicrobial agents. Concentration or intensity of an antimicrobial agent. Usually higher concentrations kill more rapidly. Relationship is not linear. 31 ©2020 McGraw-Hill Education Conditions Influencing the Effectiveness of Antimicrobial Agent Activity 2 Contact time. The longer the exposure, the more organisms killed. Temperature. Higher temperatures enhance chemical activity. Local environment. pH, viscosity, concentration of organic matter, and so on, can profoundly impact effectiveness. Organisms in biofilms are less susceptible to many antimicrobial agents. 32 ©2020 McGraw-Hill Education  Efficiency Evaluation of Chemical Agents Phenol coefficient test. Potency of a disinfectant is compared to that of phenol. Useful for screening but may be misleading. Use dilution test. Determines rate at which selected bacteria are destroyed by various chemical agents. Normal in-use testing. Testing done using conditions that approximate normal use of disinfectant. 33 ©2020 McGraw-Hill Education  Biological Control of Microorganisms Emerging field showing great promise. Natural control mechanisms: Predation by Bdellovibrio. Viral-mediated lysis using pathogen specific bacteriophage lysins (or bacteriophages themselves, such as in a spray format recently approved by the FDA for use on food products). Toxin-mediated killing using bacteriocins. 34 ©2020 McGraw-Hill Education  Take Home Message Controlling microbial growth can be achieved by many different methods—some physical, some chemical. Understanding what microbes need to grow and thrive is important for then understanding how to kill them off or control their growth. While many of these methods are useful, each has pros and cons—and each may not be suitable in particular circumstances. Always be thinking about what the appropriate and most useful way to control microbe growth in a given environment or situation might be using the information found in this chapter. 35 ©2020 McGraw-Hill Education