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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. Terminology.

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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. Terminology • Sterilization: Removal of all microbial life • Commercial Sterilization: Killing C. botulinum endospores • Disinfection: Removal of pathogens • Antisepsis: Removal of pathogens from living tissue • Degerming: Removal of microbes from a limited area • Sanitization: Lower microbial counts on eating utensils • Biocide/Germicide: Kills microbes • Bacteriostasis: Inhibiting, not killing, microbes

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

  5. Effectiveness of antimicrobial treatment depends on: • Number of microbes • Environment (organic matter, temperature, biofilms) • Time of exposure • Microbial characteristics Figure 7.1b

  6. Actions of Microbial Control Agents • Alternation of membrane permeability • Damage to proteins • Damage to nucleic acids

  7. 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

  8. Heat • Moist heat denatures proteins • Boiling • Autoclave: Steam under pressure Figure 7.2

  9. Physical Methods of Microbial Control • Pasteurization reduces spoilage organisms and pathogens • Equivalent treatments • 63°C for 30 min • High-temperature short-time 72°C for 15 sec • Ultra-high-temperature: 140°C for <1 sec • Thermoduric organisms survive

  10. Physical Methods of Microbial Control • Dry Heat Sterilization kills by oxidation • Flaming • Incineration • Hot-air sterilization

  11. Physical Methods of Microbial Control • Filtration removes microbes • Low temperature inhibits microbial growth • Refrigeration • Deep freezing • Lyophilization • High pressure denatures proteins • Desiccation prevents metabolism • Osmotic pressure causes plasmolysis

  12. Physical Methods of Microbial Control • Radiation damages DNA • Ionizing radiation (X rays, gamma rays, electron beams) • Nonionizing radiation (UV) • (Microwaves kill by heat; not especially antimicrobial)

  13. Figure 7.5

  14. Chemical Methods of Microbial Control • Principles of effective disinfection • Concentration of disinfectant • Organic matter • pH • Time

  15. Chemical Methods of Microbial Control • Evaluating a disinfectant • Phenol coefficient- compares the effectiveness of a disinfectant against the effectiveness of phenol. • Use-dilution test 1. Metal rings dipped in test bacteria are dried 2. Dried cultures placed in disinfectant for 10 min at 20°C 3. Rings transferred to culture media to determine whether bacteria survived treatment

  16. Chemical Methods of Microbial Control • Evaluating a disinfectant • Disk-diffusion method Figure 7.6

  17. Types of Disinfectants • Phenol • Phenolics. cresols from coal tar as O- phenylphenol (Lysol) • Injury lipid containing plasma membrane, Active in present of organic compound. good surface disinfectant • Bisphenols • Hexachlorophene . HAI control • Triclosan, soap, toothpaste. • (G +ve), fungi • Disrupt plasma membranes Figure 7.7

  18. Types of Disinfectants • Biguanides. Chlorhexidine • Disrupt plasma membranes • Effect on most bacteria except mycobacterium, endospores, non envolpe viruses, protozoa cyst. • Used as mouthwash, for general skin cleansing, a surgical scrub, and a preoperative skin preparation.

  19. Types of Disinfectants • Halogens. • Iodine,active aganst all kind of bacteria, many endospores, fungi, some viruses. • Proposed mechanisms by binding to some enzymes and protiens . • Tincture iodin contain alcohol, Iodophor is acompination of iodine and organic molecule.eg povidone- iodine. • Chlorine • Oxidizing agents, • Bleach is hypochlorous acid (HOCl) • Chloramines consist of ammonia use as disinectant , antiseptic and santizing.

  20. Types of Disinfectants • Alcohols. Ethanol, isopropanol • Denature proteins, dissolve lipids • No effect on endospores, and non envelope viruses. Table 7.6

  21. Types of Disinfectants • Heavy Metals. Ag, Hg, Cu • Oligodynamic action, the ability of small amounts of • heavy metals to exert a lethal effect on bacterial cells. The exact mechanism of this action is still • unknown but some data suggest that the metal ions denature protein of the target cells by binding to reactive groups resulting in their precipitation and Inactivation. • Silver nitrite used as antiseptic and eyes drop of newborns. • Cupper sulfate used to control green algae in concentration part per million. • Zinc oxide used in paints.

  22. Surface-Active Agents or Surfactants • Soaps and acid anionic detergents • The agents decrease the surface tension among molecules of a liquid; soaps and detergents are examples. • Soaps have limited germicidal action but assist in the removal of microorganisms through scrubbing. • Acid-anionic detergents are used to clean dairy equipment.

  23. Quaternary Ammonium Compounds • Quats are cationic detergents attached to NH4+. • By disrupting the plasma membranes, they allow cytoplasmic constituents to leak out of the cell. • Quats are most effective against Gram-positive bacteria, envelope viruses, fungi. • They do not kill endospores or mycobacteria. • Examples • Zephiran (benzalkonium chloride) • Cepacol (cetylpyridinium chloride) • Pseudomonas are highly resistant, can even live in quats

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

  25. Types of Disinfectants • Chemical Food Preservatives • Organic Acids • Inhibit metabolism • Sorbic acid, benzoic acid, calcium propionate • Control molds and bacteria in foods and cosmetics • Nitrate and nitrite salts prevent germination of Clostridium botulinum endospores in meats. • Antibiotics. Nisin and natamycin antifungal prevent spoilage of cheese

  26. Types of Disinfectants • Aldehydes • Aldehydes such as formaldehyde and glutaraldehyde (Gidex). • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH) • Formaldehyde gas or formalin 37% of Formaldehyde. • Glutaraldehyde used as 2% solution is bactericidal, virucidal, tuberculocidal in 10 min.

  27. Gaseous Chemosterilizers • Chemicals that sterilize in a closed chamber • Ethylene oxide is the gas most frequently used for sterilization. • Other examples include propylene oxide and beta-propiolactone. • It penetrates most materials and kills all microorganisms by protein denaturation. • It requires long exposure and is toxic and explosive when in pure form.

  28. Peroxygens (Oxidizing Agents) • Ozone, peroxide, and peracetic acid (CH3CO3H) are used as antimicrobial agents. • They exert their effect by oxidizing molecules inside cells. • Ozone supplement Cl in water disinfectant. • Used on contaminated surfaces; some deep wounds, in which they are very effective against oxygen-sensitive anaerobes.

  29. Microbial Characteristics and Microbial Control • Gram-negative bacteria are generally more resistant than gram-positive bacteria to disinfectants and antiseptics. • Mycobacteria, endospores, and protozoan cysts and oocysts are very resistant to disinfectants and antiseptics. • Non-enveloped viruses are generally more resistant than non-enveloped viruses to disinfectants and antiseptics.

  30. Microbial Characteristics and Microbial Control Figure 7.11

  31. Microbial Characteristics and Microbial Control

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