1. The Control of Microbial Growth
Chapter 7
The Control of Microbial Growth

2. The Control of Microbial Growth
Sepsis refers to microbial contamination.
Asepsis is the absence of significant contamination.
Aseptic surgery techniques prevent microbial contamination of wounds.

3. Sterilization:
Removal of
all microbial
life

4. Commercial
Sterilization:
Killing
Clostredium
botulinum
endospores

5. Disinfection:
Removal Of
pathogens

6. Antisepsis:
Removal of
pathogens
from living
tissue

7. Terminology
Degerming: Removal of microbes from a limited area( Particularly the skin).
Sanitization: Lower microbial counts on eating utensils
Biocide/Germicide: Kills microbes
Bacteriostasis: Inhibiting, not killing, microbes

8. Bacterial populations die at a constant logarithmic rate.
Figure 7.1a

9. Effectiveness of antimicrobial treatment depends on:
Number of microbes
Environment a. Organic matter b. Temperature c. Biofilms
Time of exposure
Microbial characteristics
Figure 7.1b

10. Actions of Microbial Control Agents
Alteration of bacterial plasma membrane permeability
Damage to proteins
Damage to nucleic acids

12. Physical Methods of Microbial Control
Heat
Thermal death point (TDP): Lowest temperature at which all cells in a culture are killed in 10 min.
Thermal death time (TDT): Time to kill all cells in a culture
Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature

13. Physical Methods of Microbial Control
At sea level , normal atmospheric pressure is 15 pounds per square inch psi , or 1 atmosphere.
At this pressure , water will boil at 100°C
At 20 psi (5 psi above normal) the temperature of steam is 109 °C
At 30 psi (15 psi above normal) it will be 121 °C

14. Physical Methods of Microbial Control
Moist heat
Denatures proteins
Autoclave: Steam under pressure
Figure 7.2

15. Physical Methods of Microbial Control
Autoclave
Used for heat resistant materials, glass wares , metalic instruments, liquid , paper and some media.

16. Physical Methods of Microbial Control
Pasteurization
disinfection of beverages
Pasteurization reduces spoilage organisms and pathogens
Equivalent treatments
1- 63°C for 30 min

17. Physical Methods of Microbial Control
Pasteurization
2- High-temperature short-time 72°C for 15 sec
effective against certain resistant pathogens such as Coxiella and Mycobacterium.
Inactivate most viruses and destroy the vegetative stages of 97%-99% of bacteria and fungi.
Do not kill endospores and yeasts.

18. Physical Methods of Microbial Control
Pasteurization
3- Ultra-high-temperature: 140°C for <1 sec
Thermoduric organisms survive

19. Physical Methods of Microbial Control
Dry Heat Sterilization kills by oxidation
1- Flaming
2- Incineration
Bunsen burners
Reaches 1870°C at hottest point.
laboratory instruments such as inoculating loops.
Incinerators ( °C) syringes, needles, culture materials, bandages, pathology samples.

20. Physical Methods of Microbial Control
3- Hot-air sterilization
Hot-air
Autoclave
Equivalent treatments
170˚C, 2 hr
121˚C, 15 min

21. Physical Methods of Microbial Control
Tyndalization
Steam at 100 °C for 3 days.
Used for heat sensitive culture media.
Egg, serum, carbohydrates which break down at higher temperature

22. Physical Methods of Microbial Control
Filtration
Sterilize heat sensitive materials ( culture media, enzymes, vaccines and antibiotic solutions).
The pore size of membrane filter 0.22µm and 0.45 µm

23. Physical Methods of Microbial Control
Filtration
Spirochetes and Mycoplasma pass through membrane filter.
Membrane filter with pore size µm retain viruses and large protein molecules.

24. Physical Methods of Microbial Control
Low temperature
Refrigeration (0C° - 7C° )
Reduce of reproduction.
Reduce synthesize toxins.
Bacteriostatic effect.

25. Physical Methods of Microbial Control
Deep freezing
Temperature from -70C° to -135 can preserve cultures of bacteria , viruses, and fungi for long period.
Many parasites such as round worm are killed by several days.

26. Physical Methods of Microbial Control
Lyophilization
Combination of freezing and drying.
Method of preserving microorganisms in a viable state for many years.
Pure cultures are frozen instantaneously and simultaneously exposed to a vacuum that removes water, avoiding the formation of ice crystals.
Not all cells survive.

27. Physical Methods of Microbial Control
Refrigerator
Pathogenic able to survive several months in the refrigerator.
Staphylococcus aurous
Clostredium species
Streptococcus species
Salmonella
Yeast , molds, and viruses.

28. Physical Methods of Microbial Control
Desiccation
Vegetative cells directly exposed to normal room temperature gradually become dehydrated.
Niesseria gonorrhea , Streptococcus pneumonia and the Spirochetes of syphilis die after a few hours of air dry.
Staphylococcus, Streptococcus, and the tubercle bacillus surrounded by sputum remain viable in air and dust.
Physical Methods of Microbial Control

29. Desiccation
Tuberculosis can remain viable for month.
Many enveloped viruses and fungal spores can also withstand long periods of desiccation

30. Physical Methods of Microbial Control
Desiccation
Bacterial endospores have survive for centuries.
Endospores remain in a hospital, dusts, clothing,and bedding might contain infectious microbes.

31. Physical Methods of Microbial Control
High pressure denatures proteins
Osmotic pressure causes plasmolysis
The use of high concentration of salt and sugars to preserve food is based on the effect of osmotic pressure.

32. Physical Methods of Microbial Control
Radiation
Radiation damages DNA
1- Ionizing radiation (X rays, gamma rays, electron beams) all can penetrate liquids and most solid materials.
Gamma rays are most
penetrating. X ray intermediate.

33. Physical Methods of Microbial Control
2- Non ionizing radiation (UV= ultra violet )
UV light damages DNA by formation bonds between adjacent thymine's DNA chains.
These thymine dimers inhibit correct replication of the DNA during reproduction of the cell.
UV radiation is also used to control microbes in the air.

34. Physical Methods of Microbial Control
UV lamp or germicidal lamp is commonly in hospital rooms, operating rooms, and cafeterias.
UV light is also used to disinfect vaccines and other medical products.
UV light can damage human eyes, and prolonged exposure can cause burns and skin cancer in human.

35. Physical Methods of Microbial Control

36. Physical Methods of Microbial Control
(Microwaves kill by heat; not especially antimicrobial)

37. Figure 7.5

38. Physical Methods of Microbial Control
Certain foods do not irradiate well:
The white of eggs become milky and liquid
Grape fruit gets mushy
Alfalfa seed do not germinate
No ill effects from eating irradiated food.

39. Physical Methods of Microbial Control
Radiation used for :-
Drugs
Vaccine
Medical instruments ( especially plastics ).
Syringes
Surgical gloves
Tissues such as bone, skin and heart valves for grafting.

40. Chemical Methods of Microbial Control
Factors Affecting the Efficacy of Disinfection
Concentration of disinfectant
Organic matter pH
Time

41. Chemical Methods of Microbial Control
Evaluating a disinfectant
By disk-diffusion method
Figure 7.6

42. Types of Disinfectants
Phenol
Phenolics.
O-phenylphenol
Hexachlorophene
Triclosan
Disrupt plasma membranes
Figure 7.7

43. Types of Disinfectants
Biguanides.( antimalarial drug)
Chlorhexidine (mouthwash)
Disrupt plasma membranes

44. Types of Disinfectants
Halogens. Iodine, Chlorine
Oxidizing agents
Bleach is hypochlorous acid (HOCl)
Halogens react not only with living microorganisms but also with their environment, that is, dead bacteria, dissolved proteins, and amino acids.

45. Types of Disinfectants
Alcohols. Ethanol and isopropanol
Denature proteins, dissolve lipids
Table 7.6

46. Types of Disinfectants
Heavy Metals. Ag, Hg, Cu
Silver ion at inactivating Escherichia coli  
Copper inhibit bacteria, fungi and algae.
Oligodynamic action
Denature proteins

47. Types of Disinfectants
Surface-Active Agents or Surfactants
Soap
Degerming
Acid-anionic detergents
Sanitizing
Quarternary ammonium compounds Cationic detergents
Bactericidal, Denature proteins, disrupt plasma membrane

48. Types of Disinfectants
Chemical Food Preservatives
Organic Acids :-
Sorbic acid, benzoic acid, calcium propionate.
Inhibit metabolism.
Control molds and bacteria in foods and cosmetics.
Nitrite prevents endospore germination.
Antibiotics such as Nisin and natamycin prevent spoilage of cheese.

49. Types of Disinfectants
Aldehydes such as Glutaraldehyde, formaldehyde
Inactivate proteins by cross-linking with functional groups
(–NH2, –OH, –COOH, —SH)

50. Types of Disinfectants
Gaseous Sterilants such as Ethylene oxide
Denature proteins

51. Types of Disinfectants
Peroxygens such as
Ozone O3
Hydrogen peroxide H2O2
peracetic acid
Oxidizing agents

52. Microbial Characteristics and Microbial Control
Figure 7.11

53. Microbial Characteristics and Microbial Control
Chemical agent
Effectiveness against
Endospores
Mycobacteria
Phenolics
Poor
Good
Quats
None
Chlorines
Fair
Alcohols
Glutaraldehyde