Physical and Chemical Controls of Microorganisms

1. Physical and Chemical Controls of Microorganisms

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

3. What is Microbial Death? • 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

4. Basic Principles of Microbial Control [INSERT TABLE 9.1]

5. Figure 11.1

6. Basic Principles of Microbial Control 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 Action of Antimicrobial Agents

7. Basic Principles of Microbial Control • 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 Action of Antimicrobial A

8. Protein and Nucleic Acid Synthesis • Binding to ribosomes to stop translation • Bind irreversibly to DNA preventing transcription and translation • Mutagenic agents

9. The Selection of Microbial Control Methods • Inexpensive • Fast-acting • Stable during storage • Capable of controlling all microbial growth while being harmless to humans, animals, and objects Ideally, agents should be

10. The Selection of Microbial Control 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 Factors Affecting the Efficacy of Antimicrobial Methods

11. Factors that Influence the Action of Antimicrobial Agents • 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. The Selection of Microbial Control 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 Factors Affecting the Efficacy of Antimicrobial Methods

13. The Selection of Microbial Control Methods • 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 Methods for Evaluating Disinfectants and Antiseptics

14. Methods of Physical Control • Heat as an Agent of Microbial Control • Generally, elevated temperatures are microbicidal and lower temperatures are microbistatic • Can use moist heat or dry heat

15. Physical Methods of Microbial Control [INSERT TABLE 9.4]

16. Practical Concerns in the Use of Heat: Thermal Death Measurements • 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. Common Methods of Moist Heat Control • 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

18. Physical Methods of Microbial Control [INSERT FIGURE 9.5]

19. Pasteurization • 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

20. Physical Methods of Microbial Control [INSERT TABLE 9.2]

21. Boiling Water • For disinfection and not sterilization • Expose materials to boiling water for 30 minutes

22. Dry Oven • 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

23. Physical Methods of Microbial Control [INSERT TABLE 9.4]

24. Radiation as a Microbial Control Agent • Radiation: energy emitted from atomic activities and dispersed at high velocity through matter or space • For microbial control: • Gamma rays • X rays • Ultraviolet radiation

25. Applications of Ionizing Radiation • Food products • Medical products

26. Nonionizing Radiation: Ultraviolet Rays • 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 viruses

27. Applications of Ultraviolet Radiation • Usually disinfection rather than sterilization • Hospital rooms, operating rooms, schools, food prep areas, dental offices • Treat drinking water or purify liquids

28. Physical Methods of Microbial Control • 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. Physical Methods of Microbial Control • 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 Dessication and Lyophilization

30. Physical Methods of Microbial Control • 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. Chemical Agents in Microbial Control • 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. Decontamination by Filtration: Techniques for Removing Microbes • 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

34. Physical Methods of Microbial Control [INSERT FIGURE 9.9]

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

36. Physical Methods of Microbial Control [INSERT TABLE 9.3]