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Microbial Control: Approaches, Principles, and Methods - Prof. Luzhou Xing, Study notes of Microbiology

Various approaches to controlling microbial growth through physical and chemical methods. It covers principles of control such as decontamination, degerming, sanitization, and preservation. The document also discusses situational considerations and the selection of antimicrobial procedures, focusing on factors like type of microorganism, environmental conditions, potential risk of infection, and composition of the item.

Typology: Study notes

Pre 2010

Uploaded on 11/09/2009

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Control of Microbial Growth
Chapter 5
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Control of Microbial Growth

Chapter 5

Approaches to Control

  • (^) Control mechanisms either physical or chemical
    • (^) May be a combination of both
    • (^) Physical methods
      • (^) Heat
      • (^) Irradiation
      • (^) Filtration
      • (^) Mechanical removal
    • (^) Chemical methods
      • (^) Use a variety of antimicrobial chemicals
      • (^) Chemical depends on circumstances and degree of control required
  • (^) Decontamination
    • (^) Treatment to reduce pathogens to level considered safe
  • (^) Degerming
    • (^) Mechanism uses to decrease number of microbes in an area - Particularly the skin
  • (^) Sanitized
    • (^) Implies a substantially reduced microbial population
      • (^) This is not a specific level of control
  • (^) Preservation
    • (^) Process used to delay spoilage of perishable items
      • (^) Often includes the addition of growth-inhibiting ingredients

Principles of control continued

Microbial control methods are highly variable

  • (^) Depends on situation and degree of control required - (^) Daily life - (^) Hospital - (^) Microbiology laboratories - (^) Food and food production facilities - (^) Water treatment

Situational considerations

2) Hospitals

  • (^) Minimizing microbial population very important
    • (^) Due to danger of nosocomial infections
      • (^) Patients are more susceptible to infection
      • (^) Pathogens more likely found in hospital setting » (^) Numerous organisms develop antimicrobial resistance due to high concentrations of antibiotics
    • (^) Instruments must be sterilized to avoid introducing infection to deep tissues

Situation continued

3) Microbiology laboratories

  • (^) Use rigorous methods of control
    • (^) To eliminate microbial contamination to experimental samples and environment - (^) Aseptic technique and sterile media used for growth » (^) Eliminates unwanted organisms - (^) Contaminated material treated for disposal

Situation continued

5) Water treatment facilities

  • (^) Ensures drinking water is safe
  • (^) Chlorine generally used to disinfect water
    • (^) Can react with naturally occurring chemicals
      • (^) Form disinfection by-products (DBP)
» Some DBP linked to long-term health risks
  • (^) Some organisms resistant to chemical disinfectants

Situation continued

Selection of Antimicrobial Procedure

  • (^) Selection of effective procedure is complicated
    • Each has drawbacks and procedural parameters
  • (^) Choice of procedure depends on numerous factors
    • (^) Type of microbe
    • (^) Extent of contamination
      • (^) Numbers of organisms initially present
    • (^) Environment
    • (^) Risk of infection
    • (^) Composition of infected item
2) Number of organisms initially
present
  • (^) Time it takes to kill it directly affected by population size
  • (^) Commercial effectiveness is gauged by decimal reduction time - (^) D value - (^) Time required to kill 90% of population under specific conditions

Procedure factors continued

3) Environmental conditions

  • (^) Environmental conditions strongly influence
effectiveness
  • (^) pH, temperature and presence of organic materials can increase or decrease effectiveness - (^) Most chemicals are more effective at higher temperatures and lower pH

Procedure factors continued

5) Composition of the item

  • (^) Some sterilization and disinfection methods
inappropriate for certain items
  • (^) Heat inappropriate for plastics and other heat
sensitive items

Procedure factors continued

Physical methods to control

  • (^) Moist heat
    • (^) Destroys through irreversible coagulation of
proteins
  • (^) Moist heat includes
Boiling
Pasteurization
Pressurized steam
i) Boiling (100° C)
  • (^) Destroys most microorganisms and viruses
  • (^) Not effective means of sterilization
    • (^) Does not destroy endospores
ii) Pasteurization
  • (^) Pasteur developed to avoid spoilage of wine
  • (^) Does not sterilize but significantly reduces organisms
  • (^) Used to increase shelf life of food
  • (^) Most protocols employ HTST method
    • (^) Heated to 72°C and held for 15 seconds (milk)
  • (^) Other protocol UHT
    • (^) Heated to 140°C - 150°C, held for several seconds then rapidly cooled