control of microbial growth

• Birth of the "Aseptic technique"


  1840
• Physicians Ignaz Semmelweis and Joseph Lister


  • Developed the first microbial control practices
• Microbial control techniques


  1. Hand washing with the microbe-killing chloride of lime

  2. Aseptic surgery
• Handwashing greatly decreased infection rate in patients with surgery or delivery
• Handwashing is the best way to prevent transmission of pathogens
• Methods of control of microbial growth


  • Sterilization
  • Disinfection
  • Antisepsis
  • Degerming
  • Sanitization
• Treatments for microbial death


  • Biocide
  • Germicide
  • Bacteriostasis
  • Asepsis
• Sterilization


  Removal or destruction of ALL living microorganisms
• Heating


  • The most common method used for killing microbes, including resistant endospores
• Sterilant


  A sterilizing agent
• Commercial sterilization


  Limited heat treatment where food (e.g. canned food) is subjected to heat enough only to destroy the endospores of Clostridium botulinum
• Disinfection


  Methods of microbial control directed at destroying harmful/pathogenic microorganisms, usually refers to the destruction of vegetative (non-spore forming) pathogens
• Antisepsis


  Disinfection directed at or applied to living tissue such as the skin or a wound
• Antiseptic


  Chemical used for antisepsis
• Degerming/Degermation


  Mechanical removal of microbes in a limited area
• Sanitization


  Methods of lowering microbial counts to safe public health levels and minimize the chances of disease transmission from one user to another
• Sanitization in restaurants


  • High temperature washing
  • Chemical disinfectant
• Biocide


  Killing of microorganisms in general
• Germicide


  Killing of germs, or pathogenic microorganisms
• Bacteriostasis/Bacteriostatic


  An agent that slows down bacterial growth, once removed, bacterial growth might resume
• Sepsis


  Greek for decay or putrid, indicates bacterial contamination & spread
• Asepsis


  Indicates the absence of significant contamination, "Aseptic" refers to any area/item free of any pathogen
• When bacterial populations are heated or treated with antimicrobial chemicals, they usually die at a constant rate
• If the death curve is plotted logarithmically, the death rate is constant
• Giving a disinfectant with a 90% efficiency in microbial killing
• Factors that influence effectiveness of antimicrobial treatment


  • Number of microbes
  • Environmental influences
  • Time of exposure
  • Microbial characteristics
• The more microbes there are to begin with


  The longer it takes to eliminate the entire population
• The presence of organic matter often inhibits the action of chemical antimicrobials
• Chemical antimicrobials often require extended exposure to affect more-resistant microbes or endospores
• Microbial characteristics that make a microbe more resistant from the killing effects of biocides


  • Presence of a lipopolysaccharide outer membrane
  • Porins
  • Fastidious cell walls
• Microbial control agent actions


  • Alterations on membrane permeability
  • Damage to proteins or nucleic acids (DNA)
• Damage to the membrane lipids or proteins by antimicrobial agents causes cellular contents to leak into the surrounding medium and interferes with the growth of the cell
• Denaturation


  The loss of a protein or enzyme's characteristic 3-D structure causing the loss of structure & function, breakage of hydrogen bonds & covalent bonds
• Thermal Death Point (TDP)


  Refers to the lowest temperature at which all microorganisms in a particular liquid suspension will be killed within 10 minutes
• Thermal Death Time (TDT)


  Refers to the minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature
• Decimal Reduction Time (DRT)


  Refers to the time (in minutes) in which 90% of a population of bacteria at a given temperature will be killed
• Moist heat sterilization


  Kills microorganisms primarily by coagulating proteins (denaturation), which is caused by breakage of the hydrogen bonds
• Boiling


  • Kills vegetative forms of bacterial pathogens, almost all viruses, and fungi and their spores within about 10 minutes
• Autoclaving


  Reliable sterilization with moist heat requires temperatures above that of boiling water, most commonly achieved by steam under pressure
• The higher the pressure in the autoclave, the higher the temperature