1. Microbiology: A Systems Approach
PowerPoint to accompany
Microbiology: A Systems Approach
Cowan/Talaro
Chapter 11
Physical and Chemical Control of Microbes
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Chapter 11 Topics - Controlling Microorganisms - Physical Control
- Chemical control

3. An overview of the microbial control methods.
Fig Microbial control methods

4. Controlling Microorganisms
Microbial agents
Sanitation
Effectiveness
Mode of action

5. Microbial agents -static agents -cital agents Resistance Terms
Effectiveness
Mode of action

6. -static agents Temporarily preventing the growth of microbes
Bacteriostatic
Fungistatic

7. -cital
Killing or destroying a microorganism
Germicide
Bactericide

8. Resistance Highest resistance - bacterial spores and prions
Moderate resistance - some bacteria, protozoan cysts, fungal sexual spores, naked viruses
Least resistance - most bacteria, fungal nonsexual spores and hyphae, enveloped viruses, yeast, protozoan trophozoites

9. Comparing the resistance between endospores and vegetative cells to control agents.
Table 11.1 Relative resistance of bacterial endospors and vegetative cells

10. Terms
Sterilization
Disinfection
Antisepsis
Sanitation
Degermination

11. Sterilization
A process that destroys or removes all viable microorganisms, including spores and viruses
Physical or chemical agents
Inanimate objects
Surgical instruments, commercially packaged foods

12. Disinfection
Use of physical process or chemical agent (disinfectant) to destroy vegetative pathogens.
Removes toxins
Not bacterial endospores

13. Antisepsis
Chemical agents (antiseptics) destroy or inhibit vegetative pathogens
Skin and mucous membranes

14. Sanitation Reducing the number of microorganisms
Physical chemical agents

15. Degermination Human skin - reducing the number of microorganisms
Physical and chemical agents

16. Effectiveness Number of microorganisms
Target population (bacteria, fungi, spores, viruses)
Temperature and pH
Concentration of agent
Mode of action
Interfering agents (solvents, debris, saliva, blood, feces)

17. Factors that influence the effectiveness of antimicrobial agents.
Fig Factors that influence the rate at which microbes
are killed by antimicrobial agents

18. Mode of action Cell wall Cell membrane Nucleic acid synthesis
Protein synthesis
Protein function

19. Cell wall Bacteria and fungi Agent Block synthesis
Degrade cellular components
Destroy or reduce stability
Agent
Penicillin, detergents, alcohols

20. Cell membrane All microbes and enveloped viruses Agent
Bind and penetrate lipids
Lose selective permeability (leakage)
Agent
Surfactants

21. The effect of surfactants on the cell membrane.
Fig Mode of action of surfactants

22. Nucleic acid synthesis
Irreversible bind to DNA
Stop transcription and translation
mutations
Agent
Chemical agent – formaldehyde
Physical agent – radiation

23. Protein synthesis Binds to ribosomes Agent Stops translation
Prevents peptide bonds
Agent
chloramphenicol

24. Protein function Block protein active sites
Prevent binding to substrate
Denature protein
Agent
Physical – Heat, pH change
Chemical – alcohols, acids, phenolics, metallic ions

25. The effects of heat, pH, and blocking agents on the function of proteins.
Fig Modes of action affecting protein function

26. Physical Control
Heat
Radiation
Filtration

27. Heat
Mode of action
Moist
Dry

28. Mode of action Moist heat Dry heat Thermal death time
Coagulation of proteins
Denaturation of proteins
Dry heat
Dehydration
Denaturation
Oxidation (burning to ashes)
Thermal death time

29. Moist heat Steam and pressure Tyndallization Pasteurization
Boiling water

30. Steam and pressure
Pressure above normal atmospheric pressure will result in temperatures above 100˚C
Effectively destroys spores
Sterilizes inanimate objects (glassware)
Ex. Autoclave and home pressure cooker

31. A diagram of an autoclave.
Fig Steam sterilization with the autoclave

32. Tyndallization Intermittent sterilization
Used for heat-sensitive media, canned foods
Will not destroy spores
Ex. Exposure to free-flowing steam for 30 to 60 minutes

33. Pasteurization Disinfection of beverages
Exposes beverages to 71.6 ˚C for 15 seconds
Stops fermentation
Prevents the transmission of milk-borne diseases
Salmonella, Campylobacter, Listeria, Mycobacteria
Examples: Milk industry, wineries, breweries

34. Boiling water Decontaminates at 100 ˚C for 30 minutes
Kills most non-spore forming pathogens
Examples: home sanitizing and disinfecting, disinfecting unsafe water

35. Dry heat Hot air Incineration
Temperature and time of exposure is greater than moist heat

36. Hot air Hot air Oven Effective at 150˚C to 180˚C for 2-4 hrs
Effective for inanimate objects and oils

37. Incineration Destroys microbes to ashes or gas Flame - 1870˚C
Furnace - 800˚C to 6500˚C

38. An infrared incinerator uses flame to burn or oxidize materials into ashes.
Fig Dry heat incineration

39. Effects of cold and dessication
Cold temperatures reduce the activity of some microbes, not psychrophiles
Not a disinfection or sterilization method
Dessication or dehydration kill some microorganisms
Lyophilization – freezing and drying method used to preserve microbes

40. Radiation
Types of radiation
Modes of action
Applications

41. Types of radiation Ionizing Nonionizing Gamma rays (High energy)
X-rays (Intermediate energy)
Cathode rays (least energy)
Nonionizing
Ultraviolet

42. Mode of actions
Ionizing radiation ejects orbital electrons from an atom
High energy
Penetrates liquids and solids effectively
Nonionizing radiation raises atoms to a higher energy state
Low energy
Less penetration capability
Pyrimidine dimers

43. The effects of ionizing and nonionizing radiation on DNA.
Fig Cellular effects of irradiation

44. Ultraviolet (UV) radiation can cause the formation of pyrimidine dimers on DNA.
Fig Formation of pyrimidine dimers by the action
of UV radiation.

45. Applications Ionizing radiation Nonionizing radiation
Alternative sterilization method
Materials sensitive to heat or chemicals
Some foods (fruits, vegetables, meats)
Nonionizing radiation
Alternative disinfectant
Germicidal lamp in hospitals, schools, food preparation areas (inanimate objects, air, water)

46. A gramma radiation machine (ionizing radiation) used to sterilize fruits, vegetables, meats, fish, and spices.
Fig Sterilization with Ionizing Radiation

47. A UV treatment system can be used to disinfect water.
Fig A UV treatment system for disinfection of water

48. Filtration Removes microbes and spores from liquids and air
Perforated membrane
Pore sizes vary
Applications
Liquids that are sensitive to heat
Serum, vaccines, media

49. An example of a filtration system.
Fig Membrane filtration

50. Chemical control
Widely used agents
Applications

51. Example of chemical agents, their target microbe, level of activity, and toxicity.
Table 11.5 Qualities of chemical agents used in health care

52. Applications Halogens Phenolics Surfactants Hydrogen peroxide
Detergents and soaps
Heavy metals
Aldehydes
Gases
Dyes, acids, and alkalis

53. Halogens Chlorine Iodine Disinfectant and antiseptic
Disrupt sulfhydryl groups in amino acids
Iodine
Topical antiseptic
Disruption is similar to chlorines

54. Phenolics
Vary based on functional groups attached to the aromatic ring
Examples: Hexachlorophene, Triclorsan
Microcidal
Ingredient in soaps to kitty litter
Disrupts cell walls and membranes,

55. Phenolics contain a basic phenolic aromatic ring with different functional groups.
Fig Some phenolics

56. Alcohols Ethyl alcohol, isopropyl (rubber alcohol)
70% concentration dissolve membrane lipids, disrupt cell surface tension, denatures proteins
Germicidal and skin degerming

57. Hydrogen peroxide Colorless and caustic liquid
Form hydroxyl free radicals
Effective against anaerobes
Skin and wound cleaner
Quick method for sterilizing medical equipment

58. Examples of different devices used to sterilize medical equipment.
Fig Sterile processing of invasive equipment
protects patients.

59. Detergents and soaps Quaternary ammonium (quats) Soaps Cationic
Bind and disrupt cell membrane
Low-level disinfectant in the clinical setting
Soaps
Fatty acids, oils, sodium or potassium salts
Cleaning agents
More effective if mixed with germicides

60. For detergents, the positive charge region binds bacteria and the uncharged region integrates into the cell membrane.
Fig The structure of detergents

61. Comparison between nongermicidal and germicidal soaps.
Fig Graph showing effects of handscrubbing

62. Heavy metals Mercury, silver, Inactivate proteins
Preservatives in cosmetics and ophthalmic solutions

63. Demonstration of the effects silver and gold have on microbial growth.
Fig demonstration of the oligodynamic action
of heavy metals.

64. Aldehydes Glutaraldehyde Crosslink with proteins on the cell surface
Disinfectant for surgical instruments

65. Representation of the action of glutaraldehyde.
Fig Actions of glutaraldehyde

66. Gases Ethylene oxide Reacts with functional groups of DNA and proteins
Sterilizes and disinfects plastic materials

67. Examples of different devices that use gas to sterilize equipment.
Fig Sterilization using gas

68. Dyes
Crystal violet
Effective against Gram positive bacteria
Ointments

69. Acids and alkalis Acetic acid Ammonium hydroxide
Prevents spore germination and vegetative growth
Food preservative