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2012-10-30 04:17:21

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  1. Define: sterilization, disinfection, antisepsis, asepsis, ____cidal, ____static
    • Sterilization: Removal of microbial life
    • Disinfection: Removal of pathogens from inanimate objects
    • Antisepsis: Removal of pathogens from living tissue
    • Asepsis: The absence of significant contamination
    • ___-cidal: kill microbes
    • ___-static: inhibit growth of microbes
  2. Physical methods of microbial control and how they suppress microbial growth [very in depth]
    • Heat: kills by denaturing bacterial enzymes.
    • Moist heat: kills by denaturing proteins
    • 1. Boiling kills vegetative forms of bacteria
    • 2. Autoclaving (steam under pressure)┬ákills endospores
    • 3. Pasteurization uses quick heat or long medium heat to reduce spoilage organisms and pathogens
    • Dry heat: kills by oxidation
    • 1. Incineration of biohazardous materials
    • 2. Flaming incoluation loops in lab
    • 3. Hot-air sterilization
    • II. Filtration: removes microbes
    • 1. Gases/air use mask/filters
    • 2. Liquids use membrane filters
    • III. Low temperature: only inhibits microbial growth
    • 1. Refrigeration
    • 2. Deep freezing
    • 3. Lyophilization
    • IV. High pressure: denatures proteins
    • Kills vegetative cells, not spores
    • V. Desiccation: removal of H2O prevents metabolism
    • VI. Osmotic pressure: Causes lysis
    • High salt or sugar (often in food preservation)
    • VII. Radiation: kills bacteria by damaging the DNA
    • 1. Ionizing radiation (X rays, gamma rays, electron beams)
    • 2. Nonionizing radiation (UV, wavelength 260nm)
    • 3. Microwaves kill by heat, not especially antimicrobial
  3. Types of heat-related sterilization abbreviations/meanings.
    • TDP (thermal death point): Lowest temp to kill all cells in a culture in 10 minutes
    • TDT (thermal death time): Minimal time to kill all cells in a culture at a given temperature
    • DRT (decimal reduction time): Minutes to kill 90% of population at a given temperature
  4. List the different chemical methods of microbial control and describe how each suppresses microbial growth
    • Phenolics: causes damage to plasma membrane (lysol)
    • Bisphenols: inhibits formation of membranes(hexachlorophene, triclosan)
    • Biguanides: Disrupt plasma membranes (chlorhexidine)
    • Halogens: Alter protein synthesis and membranes (Iodine) strong oxidizing agent (Chlorine)
    • Alcohols: denatures proteins, dissolve lipids eg membranes
    • Heavy metals: denature proteins by combining with sulfhydryl groups (Ag, Hg, Cu)
    • Surfactants: mechanical removal and reaction with bacterial membrane
    • Quaternary ammonium compounds: denature proteins, disrupt plasma membranes
    • Aldehydes: inactivates proteins by cross-linking with functional groups
    • Peroxygens: oxidizing agents
  5. Explain how ionizing and non-ionizing radiation kills cells
    • Ionizing radiation (X rays, gamma rays, electron beams): ionize water to generate free radicals that destroy DNA.
    • Use for sterilization of instrumentations
    • Nonionizing radiation (UV, wavelength 260nm): damage DNA by creating thymine dimers which inhibit DNA replication.
    • UV light can damage eyes, cause burns, and skin cancer
  6. Explain how type of bacteria, physiological state of the bacterial cell, and environmental conditions affect the effectiveness of chemical control of microbial growth
    • Type of bacteria: Gram pos/neg, biofilms, preferred temperature, aerobe/facultative anaerobe/etc,
    • Physiological state of bacterial cell: osmotic state, replication state, availability of nutrients
    • Environmental conditions: time exposed, material being disinfected,