Control of MG

• Sterilization


  Destruction of all forms of microbial life including endospores
• Commercial sterilization


  Heat treatment that kills endospores of Clostidium botulinum the causative agent of botulism, in canned food
• Disinfection


  Destruction of pathogenic organisms on an inanimate (lifeless) object, such as a table-top
• Antisepsis


  Destruction of pathogenic organisms on a living object, such as the skin surface
• Sanitization


  Reduction in the number of pathogens to a level deemed safe by public health guidelines
• Microbial control terminology


  • Sterilization
  • Commercial sterilization
  • Disinfection
  • Antisepsis
  • Sanitization
  • Degerming
  • Germicide
  • Bactericide
  • Fungicide
  • Virucide
  • Sporocide
  • Bacteriostatic agent
  • Sepsis
  • Asepsis
  • Aseptic techniques
• The more microbes present, the more time it takes to eliminate population
• Factors influencing effectiveness of antimicrobial treatment

  • Number of microbes
  • Type of microbes
  • Environmental influences
  • Time of exposure
• Alteration of membrane permeability

  Damage to the plasma membrane causes leakage of cell contents into the surroundings, killing the cell or at least preventing cell division
• Denaturation


  Heat and certain chemicals break hydrogen bonds that hold proteins in their characteristic 3-dimensional shape
• Damage to proteins

  Enzymes and other proteins essential for cell function are damaged
• Damage to nucleic acids

  DNA and RNA carrying the cell's genetic information and functioning in protein synthesis are damaged, usually killing the cell
• Heat


  • Most common method, effective, least expensive
  • Denatures (coagulates) cell proteins (enzymes)
• Moist heat methods


  • Boiling
  • Autoclave
  • Pasteurization
• Boiling


  98-100°C/10 min, inactivates most vegetative cells, not heat-resistant forms
• Autoclave


  Steam under pressure, 121°C/15-20 min, destroys all forms - sterilization
• Pasteurization


  Heat material, holding at specific temperature for specific length of time, cool rapidly, inactivates pathogens, reduces total microbial population, does not sterilize
• Dry heat methods

  • Hot air ovens
  • Incineration
• Hot air ovens


  160-170°C/2-3 hrs, causes oxidation of microbes, sterilizes
• Incineration


  Burning - oxidation, must be complete, used to destroy disposable items, soiled dressings, tissue specimens
• Filtration


  Solids physically separated from liquids by passage through filters with extremely small pores, does not sterilize unless pore size small enough to trap all organisms
• Radiation types


  • Ionizing rays (X-rays, gamma rays)
  • Nonionizing rays (UV light)
• Preservation methods


  • Increased osmotic pressure
  • Desiccation
  • Acid, alkaline pH
  • Decreased temperatures
  • Lyophilization - freeze-drying
• Increased osmotic pressure


  High concentrations of salt, sugar dehydrate cells, more effective against bacteria than fungi, used for food preservation
• Desiccation


  Drying, removal of water, retards but does not always kill, more effective against bacteria than fungi, used for food preservation
• Decreased temperatures


  Refrigerator (5-10°C) retards growth, freezer (below 0°C) prevents growth, does not kill all organisms
• Lyophilization - freeze-drying


  Materials rapidly frozen at temperatures well below 0°C, exposure to vacuum while in frozen state to remove moisture, very effective method of preservation
• Antimicrobial therapy involves the use of chemical agents to treat disease
• Groups of antimicrobial agents

  • Synthetic agents
  • Natural agents (antibiotics)
  • Semi-synthetic agents
• Criteria for effective antimicrobial agents

  • Selective toxicity
  • Broad spectrum
  • Non-mutagenic
  • Soluble in body fluids
  • Stable in body fluids
  • Absorbed by tissues
  • Non-allergenic to host
  • Does not disturb host's normal flora
  • Toxicity not easily altered
  • Resistance not easily acquired
  • Long shelf life
  • Reasonable cost
• Factors affecting effectiveness of chemical disinfectants

  • Concentration of chemical
  • Time allowed for chemical to work
  • pH or acidity of solution
  • Temperature
  • Presence of proteins, blood, pus, mucus secretions, feces and vomitus
• Modes of action of antimicrobial agents

  • Interfere with microbe's vital metabolic processes
  • Target structural/metabolic differences between eukaryotic and prokaryotic cells
  • Interfere with metabolic pathways
  • Interfere with cell wall (murein) synthesis
  • Interfere with protein synthesis
  • Interfere with nucleic acid replication/transcription
  • Cause damage to cell membrane
• Major groups of chemical antimicrobial agents

  • Phenol and phenolic compounds
  • Alcohols
  • Halogens
  • Heavy metals and their compounds
  • Dyes
  • Detergents
  • Quaternary Ammonium Compounds
• STERILIZATION


  Destruction of all forms of microbial life including endospores

  • This is the most often done with heat

  • There are no degrees of sterilization: an object is either sterile or not.
• COMMERCIAL STERILIZATION


  Heat treatment that kills endospores of Clostidium botulinum the causative agent of botulism, in canned food.

  • Does not kill endospores of thermophiles, which are not pathogens and may grow at temperatures above 45C
• DISINFECTION


  refers to the destruction of pathogenic organisms on an inanimate (lifeless) object, such as a table- top
• ANTISEPSIS


  refers to the destruction of pathogenic organisms on a living object, such as the skin surface
• SANITIZATION


  refers to the reduction in the number of pathogens to a level deemed safe by public health guidelines.
• DEGERMING


  Is the physical removal of microorganisms by using such things as soaps or detergents
• GERMICIDE


  any chemical agent that kills microorganisms