Chapter 5 Microbial growth control

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Chapter 5 Microbial growth control

• Physical methods
• Chemical agents
• Food Preservation

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Control of microorganisms by physical and
chemical agentsfrequently used terms

• Sterilization the process by which all living
  cells, viable spores, virus, and viroids are
  either destroyed or removed from an object or
  habitat.
• Disinfection the killing, inhibition, or removal
  of microorganisms that may cause disease.
• Sanitization the microbial population is reduced
  to levels that are considered safe by public
  health standards.
• Antisepsis the prevention of infection or sepsis
• -cide kill -static stop
• germicide kill pathogens but not necessarily
  endospores. Bactericide fungicide algicide
  viricide bacteriostatic fungistatic

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Conditions influencing the effectiveness of
antimicrobial agent activity

• 1. Population size.
• 2. Population composition. Spore, young/mature
• 3. Concentration or intensity of an antimicrobial
  agent.
• 4. Duration of exposure.
• 5. Temperature. higher
• 6. local environment.
• eg. 1. Heat kill more readily at an acid pH.
• 2. Organic matter protect microorganisms.
• 3. Biofilm protection.

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Microbial Growth Control

• Physical ways
• Heat sterilization (including autoclave and
  pasteurization)
• Radiation (microwaves, UV, X-rays, g-rays and
  electrons)
• Filtration (depth filter, membrane filter and
  nucleation track (nucleopore) filter)

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Heat(terms)

• TDP the lowest temperature at which a microbial
  suspension is killed in 10 minutes.
• TDT the shortest time needed to kill all
  organisms in a microbial suspension at a specific
  temperature and under defined conditions.
• Decimal reduction time (D) or D value the time
  required to kill 90 of the microorganisms or
  spores in a sample at a specified temperature.
  D121

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Moist heat sterilization

• Autoclave a device somewhat like a fancy
  pressure cooker.
• The air initially present is forced out the
  chamber is filled with saturated stream
• 121oC or 15 pounds 15-30min
• 1. All air must be flushed out of the chamber,
  or it will not reach 121oC even though it may
  reach pressure of 15 pounds.
• 2. The chamber should not be packed too
  tightly.

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Pasteurization

• Milk, beer, and many other beverages are treated
  with controlled heating at temperatures well
  below boiling. Not sterilize, just pasteurized.
• Past 63oC, 30min
• HTST 72oC, 15sec
• UHT 140-150oC, 1-3sec

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Dry heat sterilization

• 160-170oC 2-3h
• Suitable for glass petri dishes and pipettes
• Not suitable for heat-sensitive materials like
  many plastic and rubber items.

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Filtration

• Heat-sensitive solution
• Depth filters diatomaceous unglazed porcelain.
• Membrane filters membranes with pores about
  0.2?m in diameter are used to remove most
  vegetative cells, but not viruses.
• Air 1. Surgical masks and cotton plugs on
  culture vessels.
• 2. Biological safety cabinets.

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Radiation

• 1. Ultraviolet radiation 260nm is quite lethal
  but does not penetrate glass, dirt films, water
  and other substances.
• uv lamps the ceilings of rooms
• biological safety cabinets
• attention! uv lamp must be off
• 2 . Ionizing radiation not always as effective
  against viruses.
• Co60 cold sterilization for antibiotics,
  hormones, sutures.

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Microbial Growth Control

• Chemical ways (germicides)
• Agents that kill organisms are often called cidal
  agents (bactericidal, fungicidal and viricidal
  agents)
• Agents that do not kill but only inhibit growth
  are called static agents (bacteriostatic,
  fungistatic, and viristatic agents)
• Disinfectants are chemicals that kill
  microorganisms and are used on inanimate objects
• Antiseptics are chemical agents that kill or
  inhibit growth of microorganisms and that are
  sufficiently nontoxic to be applied to living
  tissues.

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Ideal disinfectant

• 1. Must be effective against a wide variety of
  infectious agents at high dilutions and in the
  presence of organic matter.
• 2. Toxic for infectious agents
• no toxic to people or corrosive for common
  materials.
• 3. Odorless or with a pleasant odor, soluble in
  water and low surface tension.
• 4. Relatively inexpensive

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Phenolics

• Denaturing proteins and disrupting cell
  membranes. Phenol, orthocresol(???)
• Advantages
• 1. Tuberculocidal
• 2. Effective in the presence of organic
  material.
• 3. Remain active on surfaces long after
  application.
• Disadvantages
• 1. Disagreeable odor
• 2. Cause skin irritation

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alcohols

• Bactericidal and fungicidal, not sporicidal
• 70-80 ethanol and isopropanol
• Denature proteins and dissolve membrane lipids.
• 10-15min soaking

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Halogens

• Iodine and chlorine
• Iodine oxidizing cell constituents
• iodinating cell proteins.
• 2 or more iodine in a water-ethanol solution
  of potassium iodide.
• Iodophor(???) iodine is complexed with an
  organic carries to form. water soluble,
  nonstaining, release iodine slowly to minimize
  skin burns and irritation.
• Chlorine municipal water supplies
• swimming pools. Not
  spores
• Cl2, HClO, Ca(OCl)2, oxidation

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Heavy metals

• Mercury (Hg), silver (Ag), arsenic(As), zinc
  (Zn), copper (Cu)
• 1 AgNO3 the eyes of infants to prevent
  ophthalmic gonorrhea
• Silver sulfadizine is used on burns.
• CuSO4 algicide in lakes and swimming pools.

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Aldehydes

• Combine with nucleic acids and proteins and
  inactivate them, probably by cross-linking and
  alkylating molecules.
• Sporicidal
• Formaldehyde 2 glutaraldehyde(???)

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Sterilizing gases

• Ethylene oxide gas
• 10-20 mixed with CO2 or dichlorodifluoromethane(?
  ??????)
• Relative humidity 40-50
• 38oC 5-8h or 54oC 3-4h
• EtO con 700mg/liter
• Toxic! Removed before use.

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Evaluation of antimicrobial agent effectiveness

• The phenol coefficient test
• The test bacteria Salmonella typhi
• Staphylococcus
  aureus
• a series of dilutions of phenol and the
  experimental disinfectant.
• bacteria agent 5min, 10min, 15min
  subculture to fresh medium, respectively
  incubate 2-3 days.
• The highest dilutions that kill the
  bacteria after a 10mins exposure, but not after
  5mins, are used to calculate the phenol
  coefficient.
• phenol coefficient disinfect max
  dilution/phenol max dilution
• If gt1 more effective than phenol

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Microbial Growth ControlChemotherapeutic agents

• Chemotherapeutic agents to be used internally
  for control of infectious disease, they must have
  selective toxicity, these include
• Growth factor analog
• Sulfa drugs (???)
• Amino acid analogs
• Vitamin analogs
• DNA base, RNA base analogs

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Chemotherapeutic agents Antibiotics

• Antibiotics are chemical substances produced by
  certain microorganisms that inhibit and kill
  other microorganisms, they are natural products
  rather than synthetic chemicals
• Gram-positive bacteria are usually more sensitive
  to Gram-negative bacteria
• In bacteria, the important targets of antibiotic
  action are the cell wall, the cytoplasmic
  membrane and the biosynthetic processes of
  protein and nucleic acid synthesis
• b-lactam (???) group, which includes the
  penicillins and related compounds, has major
  clinical significance

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Measuring antimicrobial activityMinimum
inhibitory concentration (MIC)
Agar diffusion method
Tube dilution technique
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Range of actions of antibiotics and other agents
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Mode of action of major antibiotics
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Food Preservation

• Sterilization
• Low temperature (best -20oC or 80oC)
• pH or acidity
• Low water availability
• Canning
• Chemical food preservation

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Questions

• several concepts
• Conditions influencing the effectiveness of
  antimicrobial agent activity?
• What are the physical- and chemical ways to halt
  microbial growth?
• On what sites do antibiotics act on cells?
• How to preserve food?