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In order to control microorganisms, you must either: Kill them Inhibit their growth.

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Presentation on theme: "In order to control microorganisms, you must either: Kill them Inhibit their growth."— Presentation transcript:


2 In order to control microorganisms, you must either: Kill them Inhibit their growth

3  When various cell structures become dysfunctional and the entire cell sustains irreversible damage  If a cell can no longer reproduce under ideal environmental conditions  Death begins when a certain threshold of microbicidal agent is met, and continues in a logarithmic manner


5 Figure 11.1

6 Action of Antimicrobial Agents Alteration of cell walls and membranes  Cell wall maintains integrity of cell  When disrupted, cannot prevent cell from bursting due to osmotic effects  Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell  When damaged, cellular contents leak out  Viral envelope responsible for attachment of virus to target cell  Damage to envelope interrupts viral replication  Nonenveloped viruses have greater tolerance of harsh conditions

7 Action of Antimicrobial A ◦ 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  Can produce fatal mutants  Can halt protein synthesis through action on RNA

8  Binding to ribosomes to stop translation  Bind irreversibly to DNA preventing transcription and translation  Mutagenic agents

9 Ideally, agents should be ◦ Inexpensive ◦ Fast-acting ◦ Stable during storage ◦ Capable of controlling all microbial growth while being harmless to humans, animals, and objects

10 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 and level of microbial control based on site of medical procedure

11  The number of microorganisms  The nature of the microorganisms in the population  The temperature and pH of the environment  The concentration of the agent  The mechanism of action of the agent  The presence of solvents, interfering organic matter, and inhibitors

12 Factors Affecting the Efficacy of Antimicrobial Methods ◦ Relative susceptibility of microorganisms  Effectiveness of germicides classified as high, intermediate, or low  High-level kill all pathogens, including endospores  Intermediate-level kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria  Low-level kill vegetative bacteria, fungi, protozoa, and some viruses

13 Methods for Evaluating Disinfectants and Antiseptics ◦ Phenol coefficient  Evaluating the efficacy of disinfectants and antiseptics by determining an agent’s ability to control microbes as a ratio to that of phenol  Greater than 1.0 indicates that agent is more effective than phenol  Has been replaced by newer methods

14  Heat as an Agent of Microbial Control ◦ Generally, elevated temperatures are microbicidal and lower temperatures are microbistatic ◦ Can use moist heat or dry heat


16 Temperature and length of exposure must be considered Higher temperatures generally allow shorter exposure times; lower temperatures generally require longer exposure times Thermal death time (TDT): the shortest length of time required to kill all test microbes at a specified temperature Thermal death point (TDP): the lowest temperature required to kill all microbes in a sample in 10 minutes

17  Steam under pressure ◦ Pressure raises the temperature of steam ◦ Autoclave is used ◦ Most efficient pressure- temperature combination for sterilization: 15 psi which yields 121°C


19 Used to disinfect beverages Heat is applied to liquids to kill potential agents of infection and spoilage, while retaining the liquid’s flavor and food value Special heat exchangers – Flash method: expose to 71.6°C for 15 seconds – Batch method: expose to 63°C to 66°C for 30 minutes Does not kill endospores or thermoduric microbes


21  For disinfection and not sterilization  Expose materials to boiling water for 30 minutes

22  Usually an electric oven  Coils radiate heat within an enclosed compartment  Exposure to 150°C to 180°C for 2 to 4 hours  Used for heat-resistant items that do not sterilize well with moist heat  effective against endotoxin


24  Radiation: energy emitted from atomic activities and dispersed at high velocity through matter or space  For microbial control: ◦ Gamma rays ◦ X rays ◦ Ultraviolet radiatio n

25  Food products  Medical products

26  Wavelength approximately 100 nm to 400 nm  Germicidal lamp: 254 nm  Not as penetrating as ionizing radiation  Powerful tool for destroying fungal cells and spores, bacterial vegetative cells, protozoa, and viruse s

27  Usually disinfection rather than sterilization  Hospital rooms, operating rooms, schools, food prep areas, dental offices  Treat drinking water or purify liquids

28 ◦ Decrease microbial metabolism, growth, and reproduction  Chemical reactions occur slower at low temperatures  Liquid water not available ◦ Psychrophilic microbes can multiply in refrigerated foods ◦ Refrigeration halts growth of most pathogens ◦ Slow freezing more effective than quick freezing ◦ Organisms vary in susceptibility to freezing

29 Dessication and Lyophilization ◦ Drying inhibits growth due to removal of water; only microbiostatic ◦ Lyophilization used for long = term preservation of microbial cultures  Prevents formation of damaging ice crystals

30  Osmotic Pressure ◦ High concentrations of salt or sugar in foods to inhibit growth ◦ Cells in a hypertonic solution of salt or sugar lose water; cell desiccates ◦ Fungi have greater ability than bacteria to survive hypertonic environments

31  Approximately 10,000 different antimicrobial chemical agents are manufactured  Approximately 1,000 used routinely in health care and the home  Occur in liquid, gaseous, or solid state  Tinctures: solutions dissolved in pure alcohol or water-alcohol mixtures


33 Effective for removing microbes from air and liquids Fluid strained through a filter with openings large enough for fluid but too small for microorganisms Filters are usually thin membranes of cellulose acetate, polycarbonate, and a variety of plastic materials Pore size can be controlled and standardizes


35  Prepare liquids that can’t withstand heat  Can decontaminate beverages without altering their flavor  Water purification  Removing airborne contaminants (HEPA filters)


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