CH 7 LEARNING OBJECTIVES.pdf

1. Key terms related to microbial control: Sterilization - the process of destroying all forms of microbial life, including spores, usually through physical or chemical means. Disinfection - reducing of number of pathogenic microorganisms to a level where they pose...

1. Key terms related to microbial control: Sterilization - the process of destroying all forms of microbial life, including spores, usually through physical or chemical means. Disinfection - reducing of number of pathogenic microorganisms to a level where they pose no danger of disease, typically by chemical agents. Antisepsis - the application of chemical agents to living tissue to prevent infection by killing or inhibiting pathogen growth. Degerming - the mechanical removal of microbes from a surface. Sanitation - the process of cleaning something to make it sanitary (free from bacteria or viruses), often by using disinfectants. Biocide/germicide - chemicals that kill microbes. Bacteriostasis - the inhibition of the growth and multiplication of bacteria. Asepsis: techniques that prevent the entry of infectious agents into sterile tissues. 2. Factors related to effective treatment: Concentration and type of disinfectant. Duration of exposure. Temperature at which the treatment occurs. Presence of organic matter that might inhibit the disinfection process. 3. Patterns of microbial death: Microbial death typically follows a logarithmic pattern where a constant proportion of the population dies in each time period. High initial microbial loads (e.g., one million bacteria) require more time for complete sterilization compared to lower loads (e.g., half-million), as each cycle of treatments kills a proportion rather than a fixed number. 4. Mechanisms of action for microbial control agents: Some target the cell wall (e.g., lysozyme), other disrupt cell membranes (e.g., detergents), or interfere with protein and nucleic acid synthesis. Agents that disrupt plasma membranes might affect human cells similarly if not used properly, as our cells also have plasma membranes. 5. Physical methods of control: Moist heat (like autoclaving, boiling, pasteurization) is more effective than dry heat as it penetrates better and is excellent at destroying microbes. Canned food sterilization aims to kill all potentially harmful organisms, including spores from bacteria like Clostridium botulinum. A can of pork takes longer to sterilize than a can of soup due to denser material, which takes longer for heat to penetrate and kill all microbes. 6. Other physical methods: Filtration - removes microbes from fluids and air. Low temperature – slow or stop microbial growth. High pressure – can denature proteins and alter cell structures. Desiccation and osmotic pressure can inhibit microbial growth by removing water from the environment. 7. Difference between ionic and non-ionic radiation: Ionic radiation – (e.g., x-rays, gamma rays) produces ions that can break DNA strands and other vital cellular components.  Non-ionic radiation (e.g., UV light) typically causes damage by forming thymine dimers in DNA, which inhibit replication and function. 8. Three main principles of effective chemical disinfection: Concentration and time – the efficacy of disinfectants depends on their concentration and the duration of exposure. Higher concentrations and longer exposure times generally increase effectiveness. Specificity of action – different disinfectants are effective against different types of microorganisms. The choice of disinfectant should match the specific microbes present. Environmental conditions – factors like temperature, pH, and the presence of organic matter can affect the activity of disinfectants. Ensuring optimal conditions can enhance disinfection. 9. Methods of action and uses of different chemical disinfectant groups: Halogen mechanism of action – halogens like chlorine and iodine are effective disinfectants. Chlorine acts by breaking the chemical bonds in microbial enzymes and proteins leading the denaturation and death. Iodine penetrates the cell wall of microbes and disrupts protein and nucleic acid structure and synthesis. Surface-active agents (surfactants) – these agents, such as quaternary ammonium compounds, decrease surface tension and disrupt microbial cell membranes, leading to leakage of cell contents and death. They are commonly used for disinfecting non-critical surfaces and are effective against bacteria and viruses but less effective against spores. 10. Use-dilution tests and the disk-diffusion method: Use-dilution test – a method to measure the effectiveness of a disinfectant against specific bacteria. Disinfectant solutions are prepared at various concentrations, and test carriers contaminated with the bacteria are placed in them for a specific time. After incubation, the samples are cultured to see if any bacteria survive. The effectiveness is determined by the lowest concentration at which no bacteria survive. Disk-diffusion method – this assay is used to evaluate the efficacy of a chemical agent by applying it on a disk placed on an agar plate where bacteria cannot grow around the disk, indicates the effectiveness of the chemical agent.