Control of Microorganisms by Physical and Chemical Agents Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 7 Control of Microorganisms by Physical and Chemical Agents

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Definition of Frequently Used Terms Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Definition of Frequently Used Terms sterilization destruction or removal of all viable organisms used on inanimate objects disinfection killing, inhibition, or removal of pathogenic organisms disinfectants agents, usually chemical, used for disinfection usually used on inanimate objects

More definitions… sanitization antisepsis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. More definitions… 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

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Antimicrobial agents agents that kill microorganisms or inhibit their growth -cidal agents kill -static agents inhibit growth

-cidal agents -cide suffix indicating that agent kills germicide Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. -cidal agents -cide suffix indicating that agent kills germicide kills pathogens and many nonpathogens but not necessarily endospores include bactericides, fungicides, algicides, and viricides

-static agents -static suffix indicating that agent inhibits growth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. -static agents -static suffix indicating that agent inhibits growth include bacteriostatic and fungistatic

The Pattern of Microbial Death Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Pattern of Microbial Death microorganisms are not killed instantly population death usually occurs exponentially microorganisms were previously considered to be dead when they did not reproduce in conditions that normally supported their reproduction however we now know that organisms can be in a viable but nonculturable (VBNC) condition once they recover they may regain the ability to reproduce and cause infection

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The pattern of microbial death Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The pattern of microbial death D = decimal reduction time

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conditions Influencing the Effectiveness of Antimicrobial Agent Activity population size larger populations take longer to kill than smaller populations population composition microorganisms differ markedly in their sensitivity to antimicrobial agents

More conditions… concentration or intensity of an antimicrobial agent Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. More conditions… concentration or intensity of an antimicrobial agent usually higher concentrations or intensities kill more rapidly relationship is not linear duration of exposure longer exposure  more organisms killed

More conditions… temperature Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. More conditions… temperature higher temperatures usually increase amount of killing local environment many factors (e.g., pH, viscosity and concentration of organic matter) can profoundly impact effectiveness organisms in biofilms are physiologically altered and less susceptible to many antimicrobial agents

The Use of Physical Methods in Control Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Use of Physical Methods in Control heat low temperatures filtration radiation

Moist heat sterilization Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Moist heat sterilization must be carried out above 100oC which requires saturated steam under pressure carried out using an autoclave effective against all types of microorganisms including spores degrades nucleic acids, denatures proteins, and disrupts membranes

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The autoclave or steam sterilizer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The autoclave or steam sterilizer

Pasteurization controlled heating at temperatures well below boiling Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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

Dry heat sterilization Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dry heat sterilization less effective than moist heat sterilization, requiring higher temperatures and longer exposure times items subjected to 160-170oC for 2 to 3 hours oxidizes cell constituents and denatures proteins

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dry heat incineration bench top incinerators are used to sterilize inoculating loops used in microbiology laboratories

Measuring Heat-Killing Efficiency Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Measuring Heat-Killing Efficiency thermal death time (TDT) shortest time needed to kill all microorganisms in a suspension at a specific temperature and under defined conditions decimal reduction time (D or D value) time required to kill 90% of microorganisms or spores in a sample at a specific temperature

Z value increase in temperature required to reduce D by 1/10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Z value increase in temperature required to reduce D by 1/10

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Low temperatures freezing refrigeration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Low temperatures freezing stops microbial reproduction due to lack of liquid water some microorganisms killed by ice crystal disruption of cell membranes refrigeration slows microbial growth and reproduction

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Filtration reduces microbial population or sterilizes solutions of heat-sensitive materials by removing microorganisms also used to reduce microbial populations in air

Filtering liquids depth filters membrane filters Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Filtering liquids depth filters thick fibrous or granular filters that remove microorganisms by physical screening, entrapment, and/or adsorption membrane filters porous membranes with defined pore sizes that remove microorganisms primarily by physical screening

Membrane filter sterilization Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Membrane filter sterilization

Nylon membrane with 0.2 μm pores Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nylon membrane with 0.2 μm pores Polycarbonate membrane with 0.4 μm pores

Filtering air surgical masks cotton plugs on culture vessels Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Filtering air surgical masks cotton plugs on culture vessels high-efficiency particulate air (HEPA) filters used in laminar flow biological safety cabinets laminar flow biological safety cabinet

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Ultraviolet (UV) Radiation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ultraviolet (UV) Radiation limited to surface sterilization because it does not penetrate glass, dirt films, water, and other substances has been used for water treatment UV treatment system for disinfection of water

Ionizing Radiation penetrates deep into objects Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ionizing 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

Sterilization with ionizing radiation Symbol on irradiated materials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sterilization with ionizing radiation Irradiation machine that uses radioactive cobalt 60 as gamma radiation sources. Fruits, vegetables, meats, fish, and spices. Symbol on irradiated materials

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Chemical Control Agents - Disinfectants and Antiseptics Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Control Agents - Disinfectants and Antiseptics

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phenolics

Phenolics commonly used as laboratory and hospital disinfectants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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

Alcohols bactericidal, fungicidal, but not sporicidal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alcohols bactericidal, fungicidal, but not sporicidal inactivate some viruses denature proteins and possibly dissolve membrane lipids

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Halogens any of five elements: fluorine, chlorine, bromine, iodine, and astatine iodine and chlorine are important antimicrobial agents

Halogens - iodine skin antiseptic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Halogens - iodine skin antiseptic oxidizes cell constituents and iodinates proteins at high concentrations may kill spores skin damage, staining, and allergies can be a problem Iodophore (e.g., Betadine) iodine complexed with organic carrier Water soluble, stable, nonstaining, and release iodine slowly Minimize skin burns and irritations

Halogens - chlorine oxidizes cell constituents Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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, but not spores can react with organic matter to form carcinogenic compounds

Heavy Metals ions of mercury, silver, arsenic, zinc, and copper Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Heavy Metals ions of mercury, silver, arsenic, zinc, and copper effective but usually toxic combine with and inactivate proteins; may also precipitate proteins

Quaternary Ammonium Compounds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Quaternary Ammonium Compounds

Quaternary Ammonium Compounds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Quaternary Ammonium Compounds detergents that have antimicrobial activity and are effective disinfectants organic molecules with hydrophilic and hydrophobic ends (i.e. amphipathic) act as wetting agents and emulsifiers cationic detergents are effective disinfectants kill most bacteria, but not Mycobacterium tuberculosis or endospores safe and easy to use, but inactivated by hard water and soap

Aldehydes highly reactive molecules Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aldehydes highly reactive molecules sporicidal and can be used as chemical sterilants combine with and inactivate nucleic acids and proteins

Effects of glutaraldehyde Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of glutaraldehyde 2% buffered solution is effective in disinfection

Sterilizing Gases used to sterilize heat-sensitive materials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sterilizing Gases used to sterilize heat-sensitive materials microbicidal and sporicidal combine with and inactivate proteins

Ethylene oxide sterilizer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ethylene oxide sterilizer

Chemotherapeutic Agents Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemotherapeutic Agents chemicals that can be used internally to kill or inhibit the growth of microbes within host cells their selective toxicity allows them to target the microbe without harming the host most are antibiotics, chemicals synthesized by microbes that are effective in controlling the growth of bacteria

Evaluation of Antimicrobial Agent Effectiveness Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Evaluation of Antimicrobial Agent Effectiveness complex process regulated by US federal agencies Environmental Protection Agency Food and Drug Administration phenol cofficient test testing of antimicrobial agents to see if they are effective and at what concentrations potency of a disinfectant is compared with that of phenol

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Other evaluation methods Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other evaluation methods use dilution test determines dilution rate at which selected bacteria are destroyed by various chemical agents use stainless steel cylinders, specific bacterial species, and appropriately diluted test disinfectants determine disinfectant concentration that kills test organisms with a 95% level of confidence in-use testing testing done using conditions that approximate normal use of disinfectant