Control of Bacterial Growth

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Control of Bacterial Growth

• Definitions
• Sterilization - Processes that kills living
  organisms including spores
• Disinfection - Destruction of vegetative
  pathogens (not spores) on inanimate surfaces
• Antisepsis A chemical method of disinfection
  from skin and mucus membranes
• Degerming - Removal of microbes from a limited
  area (alcohol swab prior to injection)
• Sanitization The removal of microbes from
  eating utensils and food preparation areas

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Control of Bacterial Growth

• Factors that influence effectiveness of
  antimicrobial treatment
• Number
• Environmental Influences
• Time of exposure
• Inherent characteristics

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Control of Bacterial Growth

• Physical Methods of Control
• Temperature Effects (Hot Cold)
• Filtration
• Desiccation
• Osmotic Pressure High Pressure
• Radiation
• See chart page 197

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Control of Bacterial Growth

• Effects of Temperature
• Moist Heat
• Dry Heat
• Pasteurization
• Refrigeration

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Control of Bacterial Growth

• Thermal Death Point (TDP) lowest temperature at
  which all microbes in liquid suspension will be
  killed with 10 min of exposure
• Thermal Death Time (TDT) minimal length of time
  for all bacteria in liquid culture to be killed
  at a given temperature
• Decimal Reduction Time (DRT) Time in which 90 of
  a population at a given temperature will be
  killed

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Control of Bacterial Growth

• Temperature - Moist Heat
• Autoclave 120-130C (15-20 lbs/in2)
• Effect on instruments
• Foil or cloth wrap solid materials
• Must use on liquids

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Control of Bacterial Growth

• Temperature - Dry Heat
• Glassware and instruments
• 160-170C for at least 90 min
• Usually foil wrap
• Incineration (loops needles)

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Control of Bacterial Growth

• Temperature - Pasteurization
• Milk 63C for 30 min (old)
• Milk 72C for 15 sec (new)
• Juices

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Control of Bacterial Growth

• Temperature - Refrigeration
• Does not usually kill
• Slows metabolism although psychrophillic
  organisms can still grow
• Best between 0 and 7 C
• Freeze thaw cycles can kill some organisms
• Used for culture preservation
• Lyophilization or freeze-drying long term storage
  effective in preserving foods

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Control of Bacterial Growth

• Filtration
• Used for heat sensitive liquids like serum or
  urea containing media
• 0.45µ or 0.22µ pores in membrane
• Often used commercially with beer, wine and fruit
  juices

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Control of Bacterial Growth

• Desiccation
• Inhibits growth more than kills
• Dried meats and vegetables
• Freeze dry processes in foods

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Control of Bacterial Growth

• Osmotic Pressure
• High concentrations of salts or sugars inhibit
  growth of bacteria examples includes jams and
  jellies, sugar and salt cured meats
• High Pressure
• High pressure is transferred evenly throughout
  culture suspension can denature proteins
  glycoproteins

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Radiation Control of Microorganisms
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Control of Bacterial Growth

• Radiation
• Short wave (X-rays, gamma rays) high penetration
  power breaks DNA
• Non-ionizing (UV) longer wave no penetrating
  power forms thymine dimers
• Organisms contain multiple repair systems