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Sterilization and Disinfection (Study Guide #2, Part 2)
Terms in this set (21)
- What is the goal of sterilization?
- Of commercial sterilization?
- The removal of ALL microbial life from an object/surface. ("no living things or cells at all"
2) Commercial Sterilization
- Enough heat to kill the most common threats to food spoilage.
- What is the goal of disinfection?
- The removal of common harmful bacteria.
- AKA Disinfectant (not completely sterile)
- What's the difference between a bacteriocide and a bacteriostatin?
- Kills bacteria
- Anything with suffix -cide
- Stops the bacteria from growing.
- Anything with suffix -stat
- How effective is boiling water?
- How about 121 degree water?
- What is an autoclave?
1) Boiling Water
- Good technique for disinfecting
- Most bacteria, parasites, and viruses are killed quickly by boiling water.
- A few are not and can survive for hours in boiling water.
2) 121 Degree Water
- Kills practically all microbes through sterilization.
- Even endospores will be killed in 15 minutes.
- A giant pressure cooker, allowing the pressure to increase, which increases the temperature.
- Steam is pumped inside.
- Define the decimal reduction time and understand how it is used.
1) Decimal Reduction Time
- (D Value) The time required to kill 90% of the microbes at a given temperature.
- Or, to reduce the microbes to 10% of original population.
2) How it is used
- Multiply the D value with the exponent of the original population.
- Describe and discuss methods involving wet heat, dry heat, low temperatures, and pressure.
1) Wet Heat (Moist heat)
- Moist heat denatures proteins and degrades DNA by separating the hydrogen bonds.
- Heat is transferred faster by moisture (steam/boiling water)
- Ex) Reaching your hand over
2) Dry Heat
- Oxidizes (or incinerates) microbes
- No worries about pressure so higher temperatures can be used.
- But actually has to work longer since heat is transferred slower by air than it is by moisture.
- Typical sterilizing oven = 2-3 hours @ 160C
- Also commonly use at lab benches with bunsen burners or bacti-cinerators ~ 1500-2500C.
3) Low Temperatures
- Kill microbes or stop growth by lowering the temperature.
- Freezing : -20C or lower; stops growth, no liquid water. Some cell death from ice crystals disrupting membranes.
- Refrigeration: 4C; greatly slows growth of most organisms, food keeps much longer, some pathogens (Listeria) are psychrophiles. (Soft cheese/deli meat)
- Kills microbes by disrupting protein folding.
- Pressure on liquid samples is evenly distributed.
- Not effective against endospores.
- Used for some food products to preserve flavor.
- How does filtration sterilize a liquid or air?
- Separates microbes from a solution or from the air.
- Air or water is sucked through a filter with very small holes; microbes are too big to pass through
- .22uM filters will keep out most bacteria, but small bacteria/viruses and pass.
- 0.01uM filters will keep out even viruses.
- Doesn't kill, just separates.
- "Small filters are more expensive and clogs more easily."
- Is Pasteurization a sterilizing or disinfecting process?
1) Pasteurization (Disinfecting Process)
- Heating at a moderately high temperature or for a short time, so the food isn't destroyed.
- Just kills off or reduces the bacterial population of a particular microbe.
- Prolongs the lifespan of a food product... but it isn't sterile!
- When is ionizing radiation more useful than UV?
1) Ionizing Radiation
- More effective when you need to penetrate through substances of sterilize the inside. (post-office packages.)
- X-Rays, gamma rays.
- Damages DNA
- Some can pass right through most substances.
- Possible to sterilize items inside and out.
- Effective against endospores.
- Not always effective against viruses.
- Are chemicals better suited for sterilization or disinfection?
- Chemical Methods can't achieve sterility.
- Few chemicals are so harmful to life that absolutely everything will be killed 100%.
- But chemicals make excellent disinfectants. (knocking down the popoulation)
- What hardy genus are phenolics useful against?
- The original disinfectant used by Joseph Lister.
- Mechanism: Break down lipid-containing structures: plasma membrane, the waxy cell wall of Myobacterium.
- What are the pros and cons of phenol disinfectants?
- Works around other organic compounds
- Kills a tough bacterium
- Irritating to the skin
- Potentially toxic: do not ingest.
- What are the pros and cons of halogen disinfectants?
(Iodine & Chlorine)
- Effective against wide variety of pathogens.
- Primarily used in liquid solutions.
- Toxic if levels get too high.
- Can be used as a gas or as a salt to disinfect surfaces or water.
- What are the pros and cons of the alcohol disinfectant?
- Evaporates rapidly
- Leaves no residue after use ("no concern for toxicity")
- Some bacteria and many viruses are resistant.
- What are the pros and cons of heavy metal disinfectants?
- Effective with small amounts of metal. (retains for a long time)
- Very Stable
- Can be toxic
- Very stable
- What are the pros and cons of surface-active agents (surfactants)?
- Inactivated by organic matter,
- Some bacteria are completely unaffected
- What are the pros and cons of preservative disinfectants?
- Very effective at keeping out specific types of harmful bacteria.
- Some may have harmful effects on humans.
- What are the pros and cons of aldehyde disinfectants?
- Incredibly effective germicide.
- Can actually sterilize rather than just disinfect.
- Highly toxic.
- Potentially carcinogenic.
- What are the pros and cons of oxidizing agent disinfectants?
- Strong germicide.
- Sporicide (can kill spores obligate anaerobes)
- Can cause tissue damage
- What kinds of wounds are particularly suited for treatment with hydrogen peroxide?
- Good for irrigating deep wounds. (bubbling can remove wounds from puncture wounds.
- What 2 cell types are particularly hardy and tough to kill? (ignoring prions)
1) Endospores of bacteria
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