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Chapter 7

Chapter 7. The Control of Microbial Growth. 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. Sterilization: Removal of all microbial life.

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Chapter 7

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  1. 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

  11. 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

  12. 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

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

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

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

  16. 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.

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

  18. Physical Methods of Microbial Control Dry HeatSterilization kills by oxidation 1- Flaming 2- Incineration • Bunsen burners • Reaches 1870°C at hottest point. • laboratory instruments such as inoculating loops. • Incinerators (800-6500°C) syringes, needles, culture materials, bandages, pathology samples.

  19. Physical Methods of Microbial Control 3- Hot-air sterilization

  20. 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

  21. 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

  22. Physical Methods of Microbial Control Filtration • Spirochetes and Mycoplasma pass through membrane filter. • Membrane filter with pore size 0.01 µm retain viruses and large protein molecules.

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

  24. 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.

  25. 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.

  26. 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.

  27. 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.

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

  29. 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.

  30. 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.

  31. 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.

  32. 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.

  33. 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.

  34. Physical Methods of Microbial Control

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

  36. Figure 7.5

  37. 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.

  38. 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.

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

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

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

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

  43. 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.

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

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

  46. Types of Disinfectants • Surface-Active Agents or Surfactants

  47. 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.

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

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

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