Topic 6 - Microbial control Flashcards
Why it important to have microbial control?
- Prevent culture contamination - Prevent equipment contamination - Increase shelf life
What is: Sterilization Disinfection Antisepsis Degermining Commercial sterilization Sanitization
Sterilization- killing/removal of all microbes Disinfection - Removing pathogens Antisepsis - Removing pathogens from living tissue Degerming - removing microbes from limited area Sanitization - lowering microbial counts Commercial sterilization - killing C.botulinum endospores which stops growth and no pathogen left
What is: biocide/germocide Bacteriostasis sepsis asepsis
Biocide/germocide - kills microbes bacterostais - inhibiting microbes (not killing) Sepsis - microbial contamination Asepsis - absense of significant contamination
What determines the level of effectiveness of treatments?
- Time of exposure - Number of microbes - Environments if they are on organic matter, have biofilms and the temperature - Microbial characteristics
What do microbial control agents do?
- Alter membrane permeability - Denature proteins - Damage nucleic acids
What are some physical control mechanisms?
- Desiccation - Osmotic pressure - Temperature - Moisture - Pressure - Radiation - Filtration
How does heat affect microbes?
It denatures their proteins,
What is TDP?
Thermal death temperature. It is the lowest temperature that kills ALL cells in 10 mins.
What is TDT?
Thermal death time. It is time during which all cells are killed.
What is DRT?
Decimal reduction time. This is the time that kills 90% of population at given temperature.
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What is autoclaving?
It is sterilization but using steam. It kills everything but prions.
What does sterilization time using the autoclave depend on?
Sterilization time depends on volume, e.g. 10 mls = 15mins
6L - 70 mins
It uses steam as opposed to water, it has higher temperatures them boiling and higher pressure.
What is an important apparatus for steam sterilization?
The sterilization strip which confirms sterilization.
What are the properties of dry heat sterilization?
- Kills by oxidation
- incineration
- flaming
- hot air sterilization.
What is the equivlance of dry heat to autoclaving?
autoclaving requires less temperature and less time.
What does pateurization do?
It reduces spoilage organisms.
What does pastuerization consists of?
High temperatures for 15 sec - 72 degrees
Ultrahigh temperatures for < 1 sec - 120 degrees
What does refrigeration do?
It slows down metabolism and is usually bacteriostatic.
What does freezing do?
Forms ice crystals which affect cells. Slow freezing is more affective than flash freezing.
What is freeze drying and what does it do?
Freeze drying helps preservation and it reduces the amount of water present.
What are the different types of filtration and what are the properties?
There is HEPA filtration which filtrates >0.3 µm and there is membrane filtration which removes 0.22µm.
Filtration doesnt…..?
- Inactivate any metabolic activity (toxins)
- Work on viruses
- Removal of moisture
- Pressure exerted which prevents osmosis when seperated by pure solvent.
- Atmospheric condition where pressure his above average.
- Emission of energy as electromagnetc waves which causes ionization.
What is the disc diffusion method?
- Add the microbe, just smear it along the entire plate.
- Add the antibiotic disc.
- Incubate which allows for bacterial growth and disc to diffuse.
What do phenols, bisphenols and phenolics do?
They all disrupt the cell membrane.
What are exmaples of bisphenols?
- hexacholophene and triclosan.
What do biguanides do? What are they used for?
They stop lipid absorption through the cell membrane, e.g. chlorohexidine.
They are used for - antiseptic, disinfection and perservation.
What are these used for..?
What are quats effective against?
Bacteria, viruses, fungi and amoebae (Benzalkonium chloride and Cetylpyridinium chloride). They do not kill enodpores or mycobacteria.
Physical and chemical barriers affect how resistant microbes are.
What is aseptic technique?
It is a procedure and practice that aims to minimise unwanted microbial contamination.
What are some examples of aseptic technique use?
- Culturing microbes
- Cell culture
- Surgery
- Wound care
What did Ehrlich discover?
That different organisms have different types of cells and therefore need unique drugs to target those cells.
What is an example of “magic bullet’? Who discovered it?
Penicilin and it was dsicvered by Fleming.
Broad spectrum - Active against both gram-negative and gram-positive bacteria, tetracyclines, phenicols etc.
Narrow - have limited activtiy and are usually used agaisnt a particular species, glycopeptides and bacitracin for gram positive and polymixins are agaisnt gram negative.
What are antibiotic modes of action?
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