Chapter 9: Controlling Microbial growth

  1. Sterilization
    Destruction of all microorganisms in or on an object
  2. Antisepsis and Disinfection
    • reduction in the number of microorganisms and viruses
    • same thing except that antisepsis is for living objects and disinfectin is for inanimate objects and can be much stronger
  3. Degerming
    • removing microbes by physical and mechanical means
    • handwashing
  4. Sanitization
    removal of pathogens from objects to meet public health standards
  5. Action of antimicrobial agents
    • alteration of cell walls and membranes
    • Damage to proteins and nucleic acids
  6. Ideally agents should be:
    • Inexpensive
    • Fast-acting
    • Stable durnig storage
    • Capable of controlling growth while being harmless to humans, animals, and objects
  7. Factors affecting the efficiency of Antimicrobial Methods
    • Site to be treated
    • Relative susceptability of microorganisms
    • the higher the temperature, the higher the efficiacy of an antimicrobial agent
  8. Germicide Classification
    • High-Level: kills all pathogens, including endospores, not prions
    • Intermediate: kills fungal spores, protozoan cysts, viruses and pathogenic bacteria
    • Low-Level: kill vegetative bacteria, fungi, protozoa, and some viruses
  9. Methods for Evaluating Disinfectants and Antiseptics (4)
    • Phenol Coefficient
    • Use-dilution test
    • Kelsey Sykes Capacity test
    • In-Use test
  10. Phenol Coefficient
    • evaluates the efficiacy of agents by comparing it's ability to control microbes to phenol
    • greater than 1.0 indicates agent is more effective
    • has been replaced by newer methods
  11. Use-dilutin test
    • metal cylinders dipped into broth cultures of bacteria
    • cylinder immersed in dilution of disinfectant
    • cylinders removed, washed, placed in medium
    • effective agents prevent growth
    • current standard test in U.S.
  12. Kelsey Sykes Capacity Test
    • bacterial suspensions added to the chemical being tested
    • samples removed at certain times and incubated
    • lack of bacterial reproduction reveals minimum time requierd for the disinfectant to be effective
  13. In-Use Test
    • swabs taken from objects before and after use of disinfectant
    • swabs innoculated into medium and incubated
    • medium monitored for growth
  14. Physical Methods of Microbial Control
    • Heat-Related Methods
    • Radiation
    • Bio-Safety Levels
  15. Heat Related Methods of Microbial Control
    • Effects of high temperature-denatures proteins, interferes with integrity of cytoplasmic membrane and cell wall
    • Moist Heat
    • Dry Heat
    • Refrigeration and Freezing
    • Dessication and Lyophilization
  16. Thermal Death Point
    lowest temperature that kills all cells in broth in ten minutes
  17. Thermal death time
    time to sterilize volume of liquid at certain temperature
  18. Decimal Reduction Time
    Time required to destroy 90% of the microbes in a sample
  19. Moist Heat (Four methods)
    • more effective than dry heat because water is a better conductor of heat than air
    • boiling
    • autoclaving
    • pasteurization
    • ultra high-temperature sterilization
  20. Moist Heat: Boiling
    • kills vegetative cells of bacteria and fungi, protozoa, and most viruses
    • boiling time is critical
  21. Moist Heat: Autoclaving
    • pressure applied to boiling water prevents steam from escaping
    • boiling temp increaes as pressure increases
    • autoclave conditions: 121*C, 15 psi, 15 min
  22. Moist Heat: Pasteurization
    • kills microbes by heating without raising the temp so much that the taste is ruined
    • used for milk, yogurt, ice cream, and juices
    • not sterilization: heat tolerant microbes survive
  23. Moist Heat: Ultrahigh-temperature sterilization
    • 140*C for one second, then rapid cooling
    • treated liquids can be stored at room temperature for months (dairy creamer)
  24. Dry Heat
    • used for materials that cannot be sterilized with moist heat (powders and oils)
    • denatures proteins and oxidezies metabolic and structural chemicals
    • requires higher temps for longer times than moist heat
    • incineration is ultimate means of sterilization
  25. Refrigeration and Freezing
    • decrease microbial metabolism, growth, and reproduction
    • chemical reactions occur slower
    • slow freezing more effective than quick freezing due to ice crystals
  26. Dessication and Lyophilization
    • drying inhibits growth due to removal of water
    • Lyophilization- technique that combines freezing and drying (used for long-term preservation)
  27. Method of Microbial Control: Radiation (two kinds)
    • Ionization
    • Non-Ionizing
  28. Ionizing Radiation
    • wavelength shorter than one nm
    • electron beams and gamma rays
    • eject electrons from atoms to create ions, ions disrupt hyrdrogen bonding, oxidized double covalent bonds, and create hyrdroxide ions which denature DNA
    • Electron beams- effective at killing, but doesnt penetrate well
    • Gamma Rays-penetrate well but requires hours to kill
  29. Nonionizing Radiation
    • wavelengths greater than one nm
    • Excites electrons, causing them to make new covalent bonds (affects 3D structure of proteinds and nucleic acids)
    • UV light causes pyrimidine dimers in DNA
    • Suitable for disinfecting air, transparent fluids, and surfaces of objects
  30. Biosafety Levels
    • Biosafetly Level 1:handling pathogens that don't cause disease in healthy humans (E.coli)
    • Biosafety Level 2:handling of moderately hazardous agents, has potential to cause disease (our Micro Lab)
    • Biosafety Level 3:handling of microbes in safety cabinets (space suits)
    • Biosafety Level 4:handling of microbes that cause severe or fatal disease, there is no cure for these (isolated labs, islands)
  31. Chemical Methods of Microbial Control
    • Affect microbes cell walls, membranes, proteins, or DNA
    • often more effective against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa
    • Phenol and phenolics
    • Alcohols
    • Halogens
    • Oxidizing Agents
    • Surfactants
    • Heavy Metals
    • Aldehydes
    • Gaseous Agents
    • Enzymes
    • Antimicrobials
  32. Chemical Methods of Microbial Control: Phenols and Phenolics
    • intermediate to low level disinfectants
    • denature proteins and disrupt cell membranes
    • effective in presence of organic matter
    • reamin active for prolonged time
    • commonly used in health care settings,labs, and homes
    • disagreeable odor and possible side effects
  33. Chemical Methods of Microbial Control: Alcohols
    • intermediate level disinfectants
    • denature proteins and disrupt cytoplasmic membrane
    • more effective than soap in removing bacteria from hands
    • swabbing skin with 70% before injecting (70% because microbes need water to metabolize)
    • Advantage: doesn't leave residue
    • Disadvantage: may not contact microbe long enough to be effective (high evaporation rate)
  34. Chemical Methods of Microbial Control: Halogens
    • intermediate level anitmicrobial, non-metallic chemicals (iodine,chlorine, bromine, fluorine)
    • effective against fungal spores and some bac. endospores
    • damage enzymes via oxidation or by denaturation
    • Widely used: water treatment, bleach, chlorine dioxide- buildings, anthrax)
  35. Chemical Methods of Microbial Control: Oxidizing Agents
    • Peroxides, Ozone, and paracetic acid
    • kill by oxidation of microbial enzymes
    • high-level disinfectants and antiseptics that work by releasing oxygen radicals
    • H2O2-sterilize surfaces, not wounds because of catalase
    • Ozone-treatment of drinking water
    • peracetic acid- effective sporocide used to sterilize equipment
  36. Chemical Methods of Microbial Control: Surfactants
    • "surface active" chemicals
    • reduce surface tension of solvents
    • soaps and detergents
    • Quartemery ammonium compounds (Quats)
  37. Quartemery ammonium compounds
    • *Surfactants in which hydrogen atoms of an ammonium ion are replaced by other functional groups
    • low level disinfectants that function by disrupting cellular membranes
    • ideal for many medical and industrail applications
    • not effective against non-enveloped viruses, mycobacterium, or endospores
  38. Chemical Methods of Microbial Control: Heavy Metals
    • Heavy-Metal Ions denature proteins (arsenic, zinc, mercury, silver, copper)
    • low-level bacteriostatic and fungaistatic agents
    • thimerosal (mercury compound) used to preserve vaccines
    • Copper controls algae growth by interfering with chlorophyll
  39. Chemical Methods of Microbial Control: Aldehydes
    • Compounds containing terminal -CHO groups
    • cross-link functional organic groups (like amino, hydroxyl,carboxyl) to dentaure proteins and inactivate nucleic acids
    • Formalin- used in embalming and disinfecting of rooms and instruments
  40. Chemical Methods of Microbial Control: Gaseous Agents
    • microbicidal and sporicidal gases used in closed chambers to sterilize items
    • denature proteins and DNA by cross-linking functinoal groups
    • used in hospitals and dentist offices
    • Disadvantages: can be hazardous,highly explosive, poisonous, and potentially carcinogenic.
  41. Chemical Methods of Microbial Control: Enzymes
    • antimicrobial enzymes act against microorganisms
    • human tears contain lysozyme (digest peptid. cell wall in bacteria)
    • Lysozyme used to decrease number of bacteria in cheese
    • prionzyme- can remove prions on medical instruments
  42. Chemical Methods of Microbial Control: Antimicrobials
    • antibiotics, semi-synthetic, and synthetic chemicals
    • antibiotics-antimicrobial chemicals produced naturally by microorganisms
    • semi-syntheic agents- chemically modified agents
Card Set
Chapter 9: Controlling Microbial growth
Flash Cards for Microbiology Exam 2 on Chapter 9 information.