module 3 Lesson 2

• Control of microorganisms


  Essential to prevent transmission of diseases and infection, stop decomposition and spoilage, and prevent unwanted microbial contamination
• Methods of controlling microorganisms

  • Physical agents
  • Chemical agents
• Physical agents


  • High or low temperature
  • Desiccation
  • Osmotic pressure
  • Radiation
  • Filtration
• Sterilization


  Process of destroying all living organisms and viruses
• Disinfection


  Elimination of microorganisms from inanimate objects or surfaces
• Decontamination


  Treatment of an object or inanimate surface to make it safe to handle
• Disinfectant


  Agent used to disinfect inanimate objects but generally too toxic to use on human tissues
• Antiseptic


  Agent that kills or inhibits growth of microbes but is safe to use on human tissue
• Sanitizer


  Agent that reduces, but may not eliminate, microbial numbers to a safe level
• Cidal


  Agent that kills microorganisms and viruses
• Static


  Agent that inhibits the growth of microorganisms
• Factors influencing antimicrobial activity

  • Concentration and kind of chemical agent
  • Intensity and nature of physical agent
  • Length of exposure
  • Temperature
  • Number of microorganisms present
  • The organism itself
  • Nature of the material bearing the microorganism
• Microorganisms


  • Have a minimum, an optimum, and a maximum temperature for growth
• Temperatures below the minimum

  Have a static action on microorganisms, inhibiting microbial growth by slowing down metabolism but not necessarily killing the organism
• Temperatures above the maximum


  Have a cidal action, denaturing microbial enzymes and other proteins
• Moist heat


  Generally more effective than dry heat for killing microorganisms due to its ability to penetrate microbial cells
• Moist heat


  Kills microorganisms by denaturing their proteins and melting lipids in cytoplasmic membranes
• Autoclaving


  1. Employs steam under pressure, raising the boiling point of water to 121°C, a temperature sufficient to kill bacterial endospores

  2. Materials are placed under 15 pounds per square inch of pressure

  3. Time varies with nature and amount of material being sterilized, generally 15-45 minutes
• Boiling water


  Will generally kill vegetative cells after about 10 minutes of exposure, but certain viruses and endospores may survive
• Dry heat


  Kills microorganisms through a process of protein oxidation rather than protein coagulation
• Dry heat


  • Hot air sterilization
  • Incineration
• Pasteurization


  Mild heating to kill particular spoilage organisms or pathogens, but does not kill all organisms
• Low temperature


  Inhibits microbial growth by slowing down microbial metabolism
• Low temperature


  • Refrigeration
  • Freezing
• Desiccation


  Generally has a static effect on microorganisms, as lack of water inhibits the action of microbial enzymes
• Osmotic pressure


  Water flows from greater water (lower solute) concentration to lesser water (greater solute) concentration, leading to plasmolysis and inhibition of growth in a hypertonic environment
• Ultraviolet radiation


  Absorbed by microbial DNA, causing thymine-thymine dimers that terminate DNA replication and lead to mutation and cell death

  
• Ionizing radiation


  Ionizes water and other molecules, disrupting DNA and proteins
• Filtration


  Microbiological membrane filters with pores small enough to prevent passage of microbes but large enough to allow organism-free fluid to pass through
• The purpose of bacteriological examination of water is to determine if there is a possibility of pathogens being present
• Coliforms


  Gram-negative, lactose-fermenting rods of the family Enterobacteriaceae, including Escherichia coli which is a direct indicator of fecal contamination
• Fecal coliform count


  Tests specifically for the fecal coliform E. coli using M-FC medium and incubation at 45.5°C
• Total coliform count


  Detects any coliforms (fecal and nonfecal) using M-coliform medium and incubation at 37°C
• Both tests use the micropore membrane filter method to trap bacteria on the filter surface for counting
• Fecal contamination


  Indicates the possibility of contamination of the water
• Micropore membrane filter method

  1. Different amounts of the water sample being tested are passed through a membrane filter

  2. The water passes through and the bacteria are trapped on the surface of the filter

  3. The filter is then placed in a petri plate on pads containing either M-FC or M-coliform medium

  4. Colonies then form on the filter

  5. By counting the number of colonies and knowing the volume of water sample used, the number of fecal coliforms or total coliforms per ml of water can be determined
• Sterilization


  The destruction of all life forms
• Disinfection


  The elimination of microorganisms from inanimate objects or surfaces
• Decontamination


  The treatment of an object or inanimate surface to make it safe to handle
• Static


  Having a non-killing effect on microorganisms