Microbiology Lecture Notes - Controlling Microbial Growth PDF

PowerPoint® Lecture Presentations prepared by Mindy Miller-Kittrell, North Carolina State University CHAPTER 9...

PowerPoint® Lecture Presentations prepared by Mindy Miller-Kittrell, North Carolina State University CHAPTER 9 Controlling Microbial Growth in the Environment © 2018 Pearson Education, Inc.  Table 9.1 Terminology of Microbial Control © 2018 Pearson Education, Inc.  Figure 9.1 A plot of microbial death rate. © 2018 Pearson Education, Inc.  Basic Principles of Microbial Control Action of Antimicrobial Agents Alteration of cell walls and membranes Cell wall maintains integrity of cell Cells burst due to osmotic effects when damaged Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell Cellular contents leak out when damaged Nonenveloped viruses have greater tolerance of harsh conditions © 2018 Pearson Education, Inc.  Basic Principles of Microbial Control Action of Antimicrobial Agents Damage to proteins and nucleic acids Protein function depends on 3-D shape Extreme heat or certain chemicals denature proteins Chemicals, radiation, and heat can alter or destroy nucleic acids Produce fatal mutants Halt protein synthesis through action on RNA © 2018 Pearson Education, Inc.  Basic Principles of Microbial Control Tell Me Why Why does milk eventually go “bad” despite being pasteurized? © 2018 Pearson Education, Inc.  The Selection of Microbial Control Methods Ideally, agents for the control of microbes should be: Inexpensive Fast-acting Stable during storage Capable of controlling microbial growth while being harmless to humans, animals, and objects © 2018 Pearson Education, Inc.  The Selection of Microbial Control Methods Factors Affecting the Efficacy of Antimicrobial Methods Site to be treated Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects Method of microbial control based on site of medical procedure © 2018 Pearson Education, Inc.  Figure 9.2 Relative susceptibilities of microbes to antimicrobial agents. © 2018 Pearson Education, Inc.  The Selection of Microbial Control Methods Factors Affecting the Efficacy of Antimicrobial Methods Relative susceptibility of microorganisms Germicide classification High-level germicides Kill all pathogens, including endospores Intermediate-level germicides Kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria Low-level germicides Kill vegetative bacteria, fungi, protozoa, and some viruses © 2018 Pearson Education, Inc.  The Selection of Microbial Control Methods Factors Affecting the Efficacy of Antimicrobial Methods Environmental conditions Temperature and pH Affect microbial death rates Alter the efficacy of antimicrobial methods Organic materials Interfere with the penetration of heat, chemicals, and some forms of radiation May inactivate chemical disinfectants © 2018 Pearson Education, Inc.  Figure 9.3 Effect of temperature on the efficacy of an antimicrobial chemical. © 2018 Pearson Education, Inc.  The Selection of Microbial Control Methods Biosafety Levels Four levels of safety in labs dealing with pathogens Biosafety Level 1 (BSL-1) Handling pathogens that do not cause disease in healthy humans Biosafety Level 2 (BSL-2) Handling moderately hazardous agents Biosafety Level 3 (BSL-3) Handling microbes in safety cabinets Biosafety Level 4 (BSL-4) Handling microbes that cause severe or fatal disease © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc.  Figure 9.4 A BSL-4 worker carrying Ebola virus cultures. © 2018 Pearson Education, Inc.  The Selection of Microbial Control Methods Tell Me Why Why are BSL-4 suits pressurized? Why not just wear tough regular suits? © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Effects of high temperatures: Denature proteins Interfere with integrity of cytoplasmic membrane and cell wall Disrupt structure and function of nucleic acids Thermal death point Lowest temperature that kills all cells in broth in 10 minutes Thermal death time Time to sterilize volume of liquid at set temperature © 2018 Pearson Education, Inc.  Figure 9.5 Decimal reduction time (D) as a measure of microbial death rate. © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Moist heat Used to disinfect, sanitize, sterilize, and pasteurize Denatures proteins and destroys cytoplasmic membranes More effective than dry heat Methods of microbial control using moist heat: Boiling Autoclaving Pasteurization Ultra-high-temperature sterilization © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Moist heat Boiling Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses Boiling time is critical Different elevations require different boiling times Endospores, protozoan cysts, and some viruses can survive boiling © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Moist heat Autoclaving Pressure applied to boiling water prevents steam from escaping Boiling temperature increases as pressure increases Autoclave conditions: 121°C, 15 psi, 15 minutes © 2018 Pearson Education, Inc.  Figure 9.6 The relationship between temperature and pressure. © 2018 Pearson Education, Inc.  Figure 9.7 An autoclave. © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Dr. Bauman’s Microbiology Video Tutor For more information, listen to Dr. Bauman describe uses of an autoclave and how an autoclave functions. © 2018 Pearson Education, Inc.  Figure 9.8 Sterility indicators. © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Moist heat Pasteurization Used for milk, ice cream, yogurt, and fruit juices Not sterilization Heat-tolerant microbes survive Pasteurization of milk Batch method Flash pasteurization Ultra-high-temperature pasteurization © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Moist heat Ultra-high-temperature sterilization 140°C for 1 to 3 seconds, then rapid cooling Treated liquids can be stored at room temperature © 2018 Pearson Education, Inc.  Table 9.2 Moist Heat Treatments of Milk © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Heat-Related Methods Dry heat Used for materials that cannot be sterilized with moist heat Denatures proteins and oxidizes metabolic and structural chemicals Requires higher temperatures for longer time than moist heat Incineration is ultimate means of sterilization © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Refrigeration and Freezing Decrease microbial metabolism, growth, and reproduction Chemical reactions are slower at low temperatures Liquid water not available Refrigeration halts growth of most pathogens Some microbes can multiply in refrigerated foods Slow freezing more effective than quick freezing Organisms vary in susceptibility to freezing © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Desiccation and Lyophilization Desiccation (drying) inhibits growth due to removal of water Lyophilization (freeze-drying) used for long-term preservation of microbial cultures Prevents formation of damaging ice crystals © 2018 Pearson Education, Inc.  Figure 9.9 The use of desiccation as a means of preserving apricots in Pakistan. © 2018 Pearson Education, Inc.  Figure 9.10 Filtration equipment used for microbial control. © 2018 Pearson Education, Inc.  Table 9.3 Membrane Filters © 2018 Pearson Education, Inc.  Figure 9.11 The roles of high-efficiency particulate air (HEPA) filters in biological safety cabinets. © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Osmotic Pressure High concentrations of salt or sugar in foods to inhibit growth Cells in hypertonic solution of salt or sugar lose water Fungi have greater ability than bacteria to survive hypertonic environments © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Radiation Ionizing radiation Wavelengths shorter than 1 nm Electron beams, gamma rays, some X rays Ejects electrons from atoms to create ions Ions disrupt hydrogen bonding, oxidize double covalent bonds, and create hydroxyl radicals Ions denature other molecules (DNA) Electron beams effective at killing microbes but do not penetrate well Gamma rays penetrate well but require hours to kill microbes X rays require long time to kill microbes Not practical for microbial control © 2018 Pearson Education, Inc.  Figure 9.12 A demonstration of the increased shelf life of food achieved by ionizing radiation. © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Radiation Nonionizing radiation Wavelengths greater than 1 nm Excites electrons, causing them to make new covalent bonds Affects 3-D structure of proteins and nucleic acids UV light causes pyrimidine dimers in DNA UV light does not penetrate well Suitable for disinfecting air, transparent fluids, and surfaces of objects © 2018 Pearson Education, Inc.  Table 9.4 Physical Methods of Microbial Control © 2018 Pearson Education, Inc.  Physical Methods of Microbial Control Tell Me Why Why are Bacillus endospores used as sterility indicators? © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Affect microbes’ cell walls, cytoplasmic membranes, proteins, or DNA Effect varies with differing environmental conditions Often more effective against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Phenol and Phenolics Denature proteins and disrupt cell membranes Effective in presence of organic matter Remain active for prolonged time Commonly used in health care settings, labs, and homes Have disagreeable odor and possible side effects © 2018 Pearson Education, Inc.  Figure 9.13 Phenol and phenolics. © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Alcohols Intermediate-level disinfectants Denature proteins and disrupt cytoplasmic membranes More effective than soap in removing bacteria from hands Swabbing of skin with alcohol prior to injection removes most microbes © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Halogens Intermediate-level antimicrobial chemicals Damage enzymes by denaturation Widely used in numerous applications Iodine tablets, iodophors, chlorine treatment, bleach, chloramines, and bromine disinfection © 2018 Pearson Education, Inc.  Figure 9.14 Degerming in preparation for surgery on a hand. © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Oxidizing Agents Peroxides, ozone, and peracetic acid Kill by oxidation of microbial enzymes High-level disinfectants and antiseptics Hydrogen peroxide can disinfect and sterilize surfaces Not useful for treating open wounds due to catalase activity Ozone treatment of drinking water Peracetic acid is an effective sporicide used to sterilize equipment © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Surfactants “Surface active” chemicals Reduce surface tension of solvents Soaps and detergents Soaps have hydrophilic and hydrophobic ends Good degerming agents but not antimicrobial Detergents are positively charged organic surfactants Quatenary ammonium compounds (quats) Low-level disinfectants Disrupt cellular membranes Ideal for many medical and industrial applications © 2018 Pearson Education, Inc.  Figure 9.15 Quaternary ammonium compounds (quats). © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Heavy Metals Heavy-metal ions denature proteins Low-level bacteriostatic and fungistatic agents 1% silver nitrate to prevent blindness caused by Neisseria gonorrhoeae Thimerosal used to preserve vaccines Copper controls algal growth © 2018 Pearson Education, Inc.  Figure 9.16 The effect of heavy-metal ions on bacterial growth. © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Aldehydes Compounds containing terminal —CHO groups Cross-link functional groups to denature proteins and inactivate nucleic acids Glutaraldehyde disinfects and sterilizes Formalin used in embalming and disinfection of rooms and instruments © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Gaseous Agents Microbicidal and sporicidal gases used in closed chambers to sterilize items Denature proteins and DNA by cross-linking functional groups Used in hospitals and dental offices Disadvantages: Can be hazardous to people Often highly explosive Extremely poisonous Potentially carcinogenic © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Enzymes Antimicrobial enzymes act against microorganisms Human tears contain lysozyme Digests peptidoglycan cell wall of bacteria Use enzymes to control microbes in the environment Lysozyme used to reduce the number of bacteria in cheese Prionzyme can remove prions on medical instruments © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Antimicrobial Drugs Antibiotics, semisynthetic, and synthetic chemicals Typically used for treatment of disease Some used for antimicrobial control outside the body © 2018 Pearson Education, Inc.  Table 9.5 Chemical Methods of Microbial Control © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Methods for Evaluating Disinfectants and Antiseptics Phenol coefficient Evaluates efficacy of disinfectants and antiseptics Compares an agent’s ability to control microbes to phenol Greater than 1.0 indicates agent is more effective than phenol Has been replaced by newer methods © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Methods for Evaluating Disinfectants and Antiseptics Use-dilution test Metal cylinders dipped into broth cultures of bacteria Contaminated cylinder immersed into dilution of disinfectant Cylinders removed, washed, and placed into tube of medium Most effective agents entirely prevent growth at highest dilution Current standard test in the United States New standard procedure being developed © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Methods for Evaluating Disinfectants and Antiseptics Kelsey-Sykes capacity test Alternative assessment approved by the European Union Bacterial suspensions added to the chemical being tested Samples removed at predetermined times and incubated Lack of bacterial reproduction reveals minimum time required for the disinfectant to be effective © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Methods for Evaluating Disinfectants and Antiseptics In-use test Swabs taken from objects before and after application of disinfectant or antiseptic Swabs inoculated into growth medium and incubated Medium monitored for growth Accurate determination of proper strength and application procedure for each specific situation © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Development of Resistant Microbes Little evidence that products containing antiseptic and disinfecting chemicals add to human or animal health Use of such products promotes development of resistant microbes © 2018 Pearson Education, Inc.  Chemical Methods of Microbial Control Tell Me Why Many chemical disinfectants and antiseptics act by denaturing proteins. Why does denaturation kill cells? © 2018 Pearson Education, Inc.