Microbiology Ch 7

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cswett
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72873
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Microbiology Ch 7
Updated:
2011-03-16 14:18:31
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Microbiology Microbial Growth
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Review questions for Ch 7 on the Control of Microbial Growth
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  1. Sepsis
    Asepsis
    Sepsis = to be contaminated (usually with bacteria or fungi)

    Asepsis = absence of contamination
  2. Sterilize
    Commercial Sterilization
    Disinfection
    • Sterilize - to completely remove all microbial life (including prions?)
    • - - best methods are heat under pressure (autoclave) and sterilizing gas (ethylene oxide)

    • Commercial Sterilization - material is heated enough to kill Clostridium botulinum endospores
    • - - heat

    • Disinfection - distruction of vegitative pathogens (vegitative pathogens (actively growing) - not endospores)
    • - - physical or chemical methods
  3. Pathogen
    A producer of disease - can be bacteral, viral, fungal, chemical
  4. Degerm
    To physically remove microbes in a limited area - swabbing for injection - uses chemical (alcohol) and physical (rubbling) at the same time - removes microbes (does not kill them)
  5. Sanitize
    • Treatment to lower microbial counts on eating utensels to safe public levels
    • - - high-temp dishwasher or chemical disinfectant
  6. Antisepsis
    Treatments for death of microbes
    Treatments to inhibit growth of microbes
    Antisepsis = to remove pathogens from living tissue

    Treatments for death of microbes end in -cide (meaning kill) - biocide, germicide

    Treatment to limit the growth of a microbe end in -stat or -stasis -bacteriostasis (limit growth by inhibing protien systhesis)
  7. When sterilized how do bacteria die?
    • Bacteria die at a constant rate of 90%/ min
    • 90% die first min
    • 90% of remaining 10% die second minute (so on)
  8. 4 factors that affect antimicrobial effectiveness
    1. # of microbes present - ↑microbes = ↓effectiveness

    2. Environment - presence of organic matter (nutrients), biofilms, temperature, pH (agents work better if warm and acidic)

    3. Time of exposure - ↑ time exposure = works better

    4. Type of microbes - Gram (+) bacteria vs. endospore state
  9. 3 ways agents kill microbes
    1. Damage to cell membrane - affects selective permeability or lipid/ protein damage causes cytoplasm to leak out

    2. Damage to intracellular proteins - break bonds and denature proteins - wont work

    3. Damage to nucleic acids - no cell growth - lethal
  10. Moist Heat Sterilization
    Dry Heat Sterilization - 3 types
    What is more effective and why?
    • Moist heat kills by denaturing proteins - called coagulation = breaks H-bonds
    • Boiling 10 mins kills most viruses everything except prions and spores

    • Dry Heat Sterilization - Dry heat kills by oxidation (breaking chemical bonds)
    • 1. Flaming - complete oxidaiton = nothing lives
    • 2. Incineration - almost complete oxidation = nothing lives
    • 3. Hot-air sterilization - charring - incomplete oxidation
    • - 2+ hours - some microbes can live if not in the oven long enough

    Moist Heat is more effective - takes lower temperature and shorter time - because the heat is water is more easily transfered to a cool body than the heat in air (hand in 100 degree water vs 100 oven)
  11. TDP
    TDT
    DRT
    TDP = Thermal death point - the lowest temperature at which all microbes are killed in 10 mins

    TDT = Thermal death time - the lowest amount of time taken to kill all microbes at a given temperature

    DRT = Decimal Reduction Time - time taken to kill 90% of the bacterial population at a given temperature
  12. What is an autoclave and how does it work?
    • Autoclave = preferred method of sterilization - kills by coagulation (denaturation) - breaks H-bonds
    • -produces steam under increased pressure - increases temperature of steam = increases effectivness
    • 15 psi (121 degrees) x 15 mins = kills everything but prions
  13. 7 physical methods of microbial control
    • 1. Heat
    • - - moist - boil, autoclave
    • - - dry - flame, incinerate, hot air (char)
    • - - pasteurize - kills pathogens

    2. Filtration - removes microbes (0.3 um filter - bacterial = 1 um)

    • 3. Cold - lowers metabolism (only inhibits growth)
    • - - refrigeration - bacteriostatic (slows spoilage rate)
    • - - Deep freeze - H20 expansion = cell disruption still has 30% survival rate
    • - - lyophilize - freeze dry under vacuum

    4. High atmospheric pressure - denatures proteins/ changes molecular structure of carbs - kills vegitative bacterial (not endospores)

    5. Desiccation = remove H20 - microbes become dormant - no effect on endospores

    6. Osmotic pressure - plasmolysis (crenation) - high salt, sugar concentraiton (honey & syrup rarely get contaminated)

    • 7. Radiation - damages DNA - kills microbe
    • - - Ionizing - X-rays, gamma rays, electron beams - ionize molecules (ionize H20 = OH hydroxyl free radical = DNA damage

    - - Nonionizing - uv (sunlight) - longer wavelenght -causes thymine dimers = DNA damage

    - - Microwaves - kills by heat and boiling - not reliable becuase solid food have an unequal distribution of moisture
  14. Pasteurization
    pasteurization lowers # of food spoilage microbes and pathgens - times vary by food (fats protect pathogens & need more time)

    Equivelent Treatments: - produce the same level of microbial reduction

    Classic - mild heating

    • HTST - High temp, short time - 72 for 15 secs
    • milk, ice cream, yogurt

    • UHT - ultra high temp - 140 for < 1sec
    • nonrefrigerated milk
  15. Hardest to kill microbes to easiest to kill
    • Prions
    • Ensospores
    • Mycobacteria
    • Cysts of protazoa
    • Vegitative protazoa
    • Gram (-) bacteria
    • Fungi & fungal spores
    • Viruses w/o envelopes
    • Gram (+) bacteria
    • Viruses w/ lipid envelopes
  16. What chemical agents produce complete sterility
    • 1. aldehydes
    • 2. ethylene oxide
  17. Principles of effective disinfection
    • 1. concentration/ dilution - of disinfectant
    • 2. organic matter - present? nutrients, feces, pus
    • 3.pH - of disinfectant
    • 4. contact - of disinfectant with microbe
    • 5. time - gradual process - can take hours
  18. phenols/ phenolics
    fat soluble → disrupts cell membrane (injures it = cell leaks)

    • 1. phenol = LYSOL - - excellent surface disinfactant - persist for long periods after application, stable, remain active in presence of organic compounds
    • -can kill mycobacteria
    • also throat spray/ losenges - has anesthetic effect as well as antibacterial

    • 2. bisphenols - Phisohex (surgical hand scrub)
    • - best on Gram (+)
    • - no longer used on infants - absorb into skin & cause neuro damage
  19. Biguanides
    disrupts cell membrane

    • Chlorhexadine - combinded with soap - surgical hand scrub or skin prep for those allergic to iodine
    • - mouth wash - kills dental plaque
    • - ineffective on endospores, mycobacteria, and most viruses.
  20. Halogens
    • one of most effective - kills almost all microbes including viruses and some endospores
    • - alters cell membrane or can enter cell (neutral charge) and hinder protein synthesis

    • Iodine (I2) - oldest and still one of most effective antiseptics
    • - Betadine - used for skin disinfection and wound treatment
    • - Iodine is also used in alcohol tinctures - tincture of iodine

    • Chlorine (Cl2) - oxidizing agent
    • Clorox - NaOCl - sodium hypochlorites - 2 drops/ liter to clean questionable drinking water
  21. Alcohols
    • ethanol, isopropanol (rubbing alcohol) 70%
    • - lipid membrane disruption
    • - protein denaturation (H2O needed - 70% alcohol most effective)

    • - kill bacterial and fungi but not endospores and nonenveloped viruses
    • - swabbing = mechanical degerming
    • - ineffective on wounds - coagulates proteins - microbes can live beneath this layer
    • - increases effectiveness of both with combined with other microbials (tincture)
  22. Heavy Metels
    • Mercury (Hg), Copper (Cu), Zinc (Zn), Silver (Ag), brass (allow of copper or zinc)
    • - denature proteins - combine with S on an a.a.

    • Oligodynamic = very small amount needed to kill
    • 1% silver nitrate - infant eyedrops to kill chlamydia & gonorrhea
  23. Soaps
    • emilsify (break up) oils
    • de-germing - mechanical only
    • amphipathic molecules - allows fats to be washed away
    • soap & detergent are interchanable terms
  24. Food Preservatives
    safe to eat & can kill microbes

    1. Organic acids - sorbic acid & benzoic acid - lowers pH - inhibits metabolism - inhibit molds that like acidic environment

    • 2. Nitrates - prevents botulism endospore germination
    • - sodium nitrate - salt created hypertonic environment
    • - turns meat red
    • - cancer concern

    • 3. Antibiotics
    • - restricted by FDA
    • - can be used as food preservative - Nisin kills endospores
  25. Aldehydes
    • Very effective killer/ preservative - can inactivate viruses
    • - inactivate proteins by forming covalent crosslinks on a.a.

    1. 2% Cidex - Glutaraldehyde - sterilizing agent - used to soak surgical instruments for hours

    2. 37% Formalin - Formaldehyde - used for tissue specimin preservation in OR

    - both can be used as enbalming agents
  26. Ethylene oxide
    • Gas - will kill everything but prions but long exposure time is needed (10 hours)
    • - flammable so mixed with CO2 or N2 (nonflammable) and applied in a closed chamber
    • - Disrupts DNA (breaks covalent bonds) and denatures proteins

    - sterilizes without heat or liquid - can be used on instruments that cannot withstand heat or steam exposure (NASA uses on space shuttles)

    - mustard gas (WW1) & antifreeze (ethylene glycol) are derivatives of it
  27. peroxygens
    oxidizing agents - kills by oxidizing cell parts that shouldnt be oxidized - O2 toxic in high concentrations

    • 1. Ozone (O3)
    • 2. Hydrogen Peroxide (H2O2) - ineffective on wounds - breaks down quickly into H2O and O2
    • 3. Benzoyl peroxide - releases O2 - anaerobes cant grow
  28. Why are Gram (-) bacteria hard to kill?
    • LPS - lipopolysaccharide on outer cell membrane
    • - porins that control what comes into the cell
  29. Why are mycobacterial hard to kill?
    thick cell wall that contains mycolic acid
  30. Why are endospores hard to kill?
    Extra thick capsule - most are resistant to chemical disinfectants
  31. Why are viruses hard to kill?
    most disinfectants are only effective against viruses with lipid envelope - can dissolve envelope and kill virus
  32. What are prions?
    Why are they hard to kill?
    Prions are self-replicating proteins - have no genetic material

    • not effected by autoclave
    • autoclave + NaOH (sodium hydroxide) treatment kinda kills them

    • Spongiform encephalopathies - Mad Cow Disease
    • CJD - Creutzfeldt- Jakob Disease - very rare - spread by prion-infected surgical instruments

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