Lecture 10: Control of Growth Flashcards
Explain the differences between sterilization , pasteurization, disinfection, decontamination, and sanitization.
Sterilzation: Everything in the specimen being killed.
Disinfection and decontamination: Checking for presence of pathogen
Sanitization and pasteurization: Reduce number of microbes.
List 3 bacterial structures and one eukaryotic structure that are hard to kill.
1-Endospores: Must be autoclaved or use glutaraldehyde.
2-Protozoal Cysts: Membrane proteins have an extensive network of disulfide proteins, making their wall tough and rigid and resistant to chemical damage. Not dry so can be killed via boiling.
3-Mycobacterium: Contain mycolic acids in their outer membrane. Mycolic acids make the mycobacterium acid-fast.
4-Biofilms (pseudomonas): Have persistor cells that are long term survivors.
Explain why naked viruses are harder to kill than enveloped viruses.
Contain matrix proteins between the envelope and capsid. Hydrophobic effect holds the membranes together, without water you lose the membrane integrity and this is what makes them easy to kill. If the membrane is lost, the matrix proteins, which are responsible for viral replication, will leave the virus and it will die.
Explain the concept of decimal reduction time, and how it depends on the organism you’re trying to kill, the surface you’re trying to decontaminate, and the decontaminant used.
- Decimal reduction time: The amount of time it takes to kill 90% (1 log) of the organisms in the culture.
- Depends on the organism based on how resistant the organism is to death.
- Depends on if the surface is porous or if it has grease or oil because most decontaminants are water based and water does not mix with grease or oil.
- Depends on the decontaminate used because some are stronger than others.
Differentiate between critical, semicritical, and non-critical medical instruments.
Critical: Direct contact with body tissues. Ex: Scalpel.
Semi-critical: Contact with mucous membranes. Ex: Endoscope.
Non-critical: External contact only. Ex: Hand sanitizer.
Explain why moist heat is a more effective decontaminant than dry heat.
water has a high heat capacity and therefore can transfer heat better to the bacteria.
Describe how an autoclave is used.
An autoclave uses steam at 121 degrees Celsius to sterilize.
List 3 methods that have been used to pasteurize liquids.
1-HTST pasteurization: High temp (72 degrees), short time (15 seconds. Denatures proteins and the flavor is altered.
2-UHT pasteurization: Ultra high temp for extremely short time. Flavor is extremely altered. Use surface with 150 degree temp.
3-Long time, low temperature (63 degrees) pasteurization. Below protein denaturing.
Describe the difference between a membrane filter and a depth (HEPA) filter.
Membrane filter has pores of a defined size (0.2um), depth filter has fibers. The depth can be changed depending on what is to be caught. Depth filter used for gases, membrane filter used for liquids.
Understand what types of radiation can and cannot be used to kill bacteria.
Irradiation: The shorter the wavelength the better. Sterilization at less than 300 nm. Damages DNA by altering hydrogen bonds between bases and breaking the phosphodiester bonds.
Ionizing radiation: Breaks phosphodiester bonds (gamma rays and X-rays). Used for foods and heat sensitive surgical materials.
UV rays: Good for surfaces only, do not penetrate deeply and are sometimes used in wastewater facilities.
List 3 bacterial structures that can serve as targets for chemical disinfectants.
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Distinguish between high-level, intermediate-level and low-level disinfectants.
Sterilant kills everything.
High-level kills everything except for spores.
Intermediate-level kills everything including mycobacterium but not including naked viruses.
Low-level kills anything below mycobacterium.
Describe the mode of action of alcohol, aldehydes, chlorhexidine, ethylene oxide, halogens, heavy metals, peroxide, phenols and quaternary amines.
Alcohols: Make sure it evaporates but not too quickly (concentration).
Aldehydes: Cross-link membrane proteins
Biguanides: Make membrane leaky.
Ethylene oxide: Gaseous sterilant that oxidizes DNA.
Halogens: Oxidize proteins especially tyrosine.
Heavy metals: Derivitize cysteine to prevent protein disulfide bonds. Chlorine is a sterilant and iodine is an intermediate level disinfectant.
Oxidizing agents: Oxidize proteins. Peroxides work much better on inanimate surface than skin.
Phenolics: Dissolve lipid membranes. Parabens are very commonly used in cosmetics. Triclosan has become resistant and started targeting lipid synthase.
Quaternary Ammonium Salts: Dissolve membranes. Used in soaps and cosmetics.
Tell the story of the (in)famous Cryptosporidium outbreak in Milwaukee in 1993 (the largest single water-associated disease outbreak in US history).
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Explain to a person who is not taking BIOL 221 how the overuse of triclosan has lead to increased bacterial resistance to this antibiotic.
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