THE CONROL OF MICROBIAL GROWTH

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CHAPTER 12

• THE CONROL OF MICROBIAL GROWTH

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Terminology of Microbial Control

• Sterilization
• Commercial Sterilization
• Disinfection
• Antisepsis
• Antiseptic vs Disinfectant
• Degerming

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Terminology of Microbial Control

• Sanitization
• Biocide or Germicide
• Bacteriostasis
• Sepsis
• Asepsis
• Aseptic techniques

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Rate of microbial death

• Factors influencing rate of microbial death
• number of microbes
• Higher number longer time
• environmental influences
• Organics, ph, temp
• time of exposure
• longer exposure time for resistant bacteria
• microbial characteristics
• Cell wall, endospores, capsule

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Actions of Anti-Microbial Agents

• alter membrane permeability
• damage of membrane lipids of proteins can cause
  cell to leak and interfere with cell growth
• damage proteins and nucleic acids
• enzymes
• DNA and RNA
• damage prevents cell replication and metabolism

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Physical Methods of Microbial Control

• Heat (moist dry)
• Filtration
• Low temperature
• High pressure
• Desiccation
• Osmotic pressure
• Radiation

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• Heat
• Moist heat kills microbes primarily by
  denaturing proteins
• Boiling kills most vegetative forms in 10 min
• Autoclave steam under pressure
• Sterilization occurs at 15 psi, 121OC for 15 min
• Pasteurization mild heating sufficient to kill
  most microbes without damaging the taste of the
  product
• Some heat resistant bacteria survive
• unlikely to spoil milk due to refrigeration
• The higher the temp, the shorter the exposure
  time
• Dry heat kills by oxidation.
• Flaming and dry heat sterilization
• Requires higher temp and longer exposure
• 170C for 2 hours is equivalent to autoclaving at
  121C for 15 minutes

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• 2. Filtration
• HEPA filters (high efficiency particulate air
  filters) remove all microbes larger than 0.3
  microns in diameter
• Some membrane filters have pores as small as 0.01
  microns
• small enough to trap viruses and even large
  proteins
• 3. Low temperatures
• Some microbes can grow at temps below freezing
• Slow freezing causes formation of ice crystals
• Thawing is actually more damaging than the
  freezing
• 4. High Pressure
• Endospores are resistant
• Kills vegetative cells by denaturing proteins
• Used to sterilize liquid food products while
  preserving flavor, taste, appearance, and
  nutritional value

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• 5. Desiccation
• Rresistance to desiccation varies by species
• cant reproduce or grow, but may remain viable
• viruses are usually more resistant
• not as much as endospore forming bacteria
• 6. Osmotic pressure
• create a hypertonic environment causing the cell
  to loose water
• Preserved fruits (sugar), cured meat (salt), and
  pickles (salt)
• 7. Radiation
• depends on wavelength, intensity and duration
• Used in sterilization of food products,
  disposable medical equipments, and pharmaceuticals

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Chemical Methods

• Evaluating a disinfectant
• Phenol coefficient test
• Use-dilution test
• Current standard
• Disk-diffusion method
• Kirby-Bauer Test

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Disk-Diffusion Method
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• Types of Chemicals
• Phenol and phenolics
• Phenol Disrupts plasma membrane, denatures
  proteins
• Rarely used, irritating qualities and bad odor
• Penolics - Disrupts plasma membrane, denatures
  proteins
• Disinfect for surfaces and skin
• Bisphenols - Disrupts plasma membrane
• Used in antimicrobial soaps and lotions
• Halogens
• various effects denature proteins, strong
  oxidizers
• Iodine antiseptic
• Chlorine - disinfectants

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• Alcohols Denature proteins and lipid
  dissolution
• Affect vegetative forms of bacteria, fungi, and
  enveloped viruses
• ethanol and isopropanol - degermer and
  disinfectant
• 70 solution is most effective
• Heavy metals Denature enzymes and other vital
  proteins
• Skin disinfectant, algicide, silver nitrate in
  newborns eyes prevents spread of gonorrhea

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• Surfactants
• Soap
• breaks down oily film into droplets
  (emulsification)
• Used for skin degerming
• Least effective of all chemical methods
• Anionic Detergents enzyme inactivation
• Commercial sanitizers
• Cationic Detergents enzyme inhibition, protein
  denaturation, disruption of plasma membrane
• disinfectant and antiseptic
• Quaternary ammonium compounds (Quats)
• most widely used cationic detergents
• Pseudomonas grows in Quat compounds

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• Food preservatives
• Added to foods to slow spoilage
• Organic acids Sodium benzoate, Sorbic acid
• Prevent molds from growing in acidic foods
• Calcium propionate - fungicide used in bread
• Inhibit mold growth by interfering with plasma
  membrane
• Nitrates- added to many meat products
• prevents germination and growth of botulism
  endospores
• preserves the pleasing red color

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• Antibiotics not meant for ingestion or
  injection useful in food preservation
• Nisin- added to cheese to inhibit growth of
  endospore formers
• Natamycin antifungal used in food (mostly
  cheese)
• Why should medical antibiotics not be used in
  food preservation?
• Aldehydes
• Among the most effective antimicrobial agents
• Denature proteins
• Disinfectant and preservative
• Formaldehyde and glutaraldehyde

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• Peroxygens oxidizing agents
• Disinfectants
• Ozone supplements chlorine in water treatment
• Hydrogen peroxide good disinfectant not
  antiseptic
• Where do the bubbles come from?
• Gaseous chemosterilizers
• Eethylene oxide gas is used to sterilize in a
  closed chamber
• 4 -18 hours exposure kills all microbes
• Denatures proteins
• Useful for heat sensitive materials
• High penetration, does not involve high
  temperatures
• Used in hospitals and to sterilize spacecrafts