2. Control of Microorganisms Microbiology 2314

3. Control of Microbial Growth Effected in two basic ways: • By Killing Microorganisms • By inhibiting the Growth of Microorganisms Usually involves the use of: • Physical Agents • Chemical Agents

4. Level of Resistance • Endospores • Mycobacteria • Fungal Spores • Small Non-enveloped Viruses - Polio, Rotavirus, Rabies • Vegetative Fungal Cells • Enveloped Viruses - Herpes, Hepatitis B & C, HIV • Vegetative Bacteria

5. Principles of Microbial Control (Definitions) • Prevention / Control of Growth to Prevent Infection and Spoilage

6. Principles of Microbial Control (Definitions) • Sterilization / Complete Destruction - No degrees of sterilization (All or Nothing) - Utilizes a. Heat b. Radiation c. Chemicals d. Physical Removal

7. Once something is sterilized, it will remain sterile if properly sealed. Sterilization is performed on surgical equipment, needles, and certain lab equipment in order to prevent the spread of microorganisms.

8. Sterilization is an extreme level of cleanliness that is usually not required outside of a medical, industrial, or laboratory environment. • In everyday environments, disinfection of objects is considered a more practical option. Nano Disinfection Scanner

9. Principles of Microbial Control • Commercial Sterilization / Heat Treatment of Canned Foods

10. Principles of Microbial Control • Disinfection / Reducing Growth NonlivingSurfaces

11. Disinfection may not necessarily eliminate spores or all of the microorganisms from an object or environment. • While disinfection is not as extreme as sterilization, but it is considered to be an adequate level of cleanliness for most situations. • Examples of disinfectants include iodine solution, copper sulfate, ozone, and chlorine gas.

12. Principles of Microbial Control • Antisepsis / Reducing Growth on Living Tissue

13. Principles of Microbial Control • Antiseptics are generally less toxic than disinfectants because they must not cause too much damage to the host living tissue. • Examples of antiseptics include iodine, 70% ethanol and 3% hydrogen peroxide.

14. Principles of Microbial Control • Degerming / Swab the Skin

15. Principles of Microbial Control • Sanitize Subject to High Temperature Washing (Dishwashers)

16. Principles of Microbial Control • Cide – Suffix Meaning to Kill • Stat – Suffix Meaning to Inhibit • Sepsis – Bacterial Contamination • Asepsis – Lack of Bacterial Contamination

17. Rate of Microbial Death • Bacteria Usually Die At a Constant Rate • Plotted Logarithmically This Will Give a Straight Line

18. Time to Kill in Proportion to the Population Size • Large Numbers Require Greater Time • Small Numbers Require Less Time

19. Susceptibilities Vary • Endospores are Difficult to Kill • Organic Matter May Interfere with Heat Treatments and Chemical Control Agents

20. Control Agents Act By • Alteration of Membrane Permeability - Susceptibility of membrane is due to its lipid and protein composition - Control Agents can alter permeability • Damage to Proteins and Nucleic Acids - Break hydrogen and covalent bonds in proteins - Interfere with DNA, RNA, Protein Synthesis

21. Denatures Proteins

22. Physical Methods of Microbial Control

23. Physical Methods • Heat • Filtration • Low Temperatures • Desiccation • Osmotic Pressure • Radiation

24. Heat • Most Frequent and Widely Used. • Always Consider 1. Type of Heat 2. Time of Application 3. Temperature • Endospores are the most heat resistant of all cells.

25. Moist Heat / Denatures Enzymes • Moisture improves heat penetration, making sterilization by moist heat more effective then dry heat. • Includes boiling and autoclaving.

26. Rare types of bacteria are capable of growing at high temperatures. • These bacteria are classified as thermophiles and hyperthemophiles. • These organisms normally growth in unusually hot environments, including hot springs and deep-sea vents. • Clearly sterilization by heat may not be the most efficient method to eliminate these types of bacteria, but they are almost never found in common environments and they are not pathogenic.

27. Thermal Death Point • Thermal Death Point (TDP) / Lowest Temp to Kill All the Bacteria in a Broth in 10 Minutes. • This aspect of thermal death is useful in purifying water via boiling. • Boiling -- Kills Many Vegetative Cells and Inactivates Viruses Within 10 Minutes (30 Minutes to be Safe) but has no effect on spores

28. Thermal Death Time • Thermal Death Time (TDT) / Time Span Required to Kill All the Bacteria in a Broth at a Given Temperature. • It was developed for food canning and has found applications in cosmetics and pharmaceuticals.

29. Decimal Reduction Time • Decimal Reduction Time (DRT) / Length of Time in Which 90% of a Bacterial Population will be Killed at a given Temperature • Reduces the number of organisms to 1/10 the initial level. • Used in Commercial Sterilization.

30. Autoclaving (Moist Heat Sterilization) • Steam Under Pressure • 121° C for 15 Minutes at 15 lb/in2 • Heat-labile Substances will be Denatured • Steam Must Contact the Material

31. Dry Heat Sterilization • Direct Flaming • Incineration • Hot-Air Sterilization (Oven)

32. Incineration • Burns and Physically Destroys Organisms • Used for • a. Needles • b. Inoculating Wires • c. Glassware • d. Body Parts?

33. Dry Heat (Hot Air Oven) • 160° C for 2 Hours or 170° C for 1 hour • Used for • a. Objects That Won’t Melt • b. Glassware • c. Metal

34. Pasteurization • A High Temperature Is Used For a Short Time • Batch Method 63 °C for 30 Minutes

35. Pasteurization is a process used in preserving heat sensitive foods such as milk, beer, and other beverages.

36. Pasteurization uses mild temperatures (63°C for 30 minutes or 71°C for 15 seconds) to kill pathogens and reduce levels of non-pathogenic organisms that cause milk and other foods to spoil

37. Pasteurization is not a method of sterilization, which is why pasteurized foods will eventually spoil if given enough time.

38. Pasteurization extends the shelf life of a product and reduces the level of pathogens in the product.

39. A new method called ultrahigh temperature (UHT) sterilization involves heating at 140°C for 3 seconds. • Milk that has been treated in this way can be kept at room temperature for 2 months with only minimal changes in flavor.

40. Filtration • The passage of a liquid or gas through a filter with pores small enough to retain microbes. • Especially important to sterilize solutions which would be denatured by heat (antibiotics, injectable drugs, amino acids, vitamins.)

41. HEPA Filters • HEPA filters are High-Efficiency Particulate Air filters designed for the filtration of small particles. Certified HEPA filters must capture a minimum of 99.97% of 0.3 microns contaminants.

42. HEPA Filters • Filtration is the primary method of eliminating pathogens from the air supply. 1. Operating Rooms 2. Burn Units 3. Fume Hoods 4. Isolation Rooms 5. Bio-cabinets 6. Pharmaceutical Manufacturing Facilities

43. Low Temperatures • Decreasing Temperature Decreases Chemical Activity • Low Temps are Not Bactericidal

44. Desiccation • Disrupts Microbial Metabolism • Stops Growth / Microbes Are Still Viable • Freeze-drying / Dehydration • Viruses and Endospores Can Resist Desiccation

46. Osmotic Pressure • Plasmolysis • Sugar Curing / Salting • May Still Get Some Mold or Yeast Growth

47. Radiation • Acts By Destroying DNA or Damaging It. • Its Efficiency is Dependent on the Wavelength, Intensity, and Duration

48. UV Radiation • The most lethal type of radiation is ultraviolet radiation with a wavelength of 260 nm. This is the wavelength most actively absorbed by DNA. • It is useful for disinfecting surfaces, air and liquids.

49. Unfortunately, this type of radiation does not penetrate dirt, glass, water, or other substances. If a surface is dusty, then complete inactivation of all microorganisms may not occur. • Due to its poor penetration, UV radiation is only useful for disinfecting outer surfaces.

50. UV Radiation • This type of radiation is also harmful if someone is directly exposed to it (for extended periods of time), as it may damage the skin and eyes.