Lab 4 Flashcards
What is sterilisation?
physical or chemical procedure that destroys all microbial life including highly resistant endospores
In the hospital, sterilisation is applicable to what?
organisms which exist on inanimate objects
What is the major sterilising agent used?
moise heat, by steam autoclave
What is an alternative sterilising agent?
Dry heat. this is useful for equipment which would be damaged by steam, and for pharmaceuticals in powder formation
What other methods can be used to sterilise things which cannot withstand moist heat? e.g. catheters, syringesm petri dishes
gamma radiation or exposure to ethylene oxide
What is filtration used for?
sterilising liquids which are sensitive to heat e.g. some pharmaceuticals
what is disinfection?
a mechainsm for reducing the level of contamination
it removes recognised pathogenic microorganisms but not necessarily all microbial forms (e.g. bacterial endospores)
What does disinfection lack, but sterilisation achieves?
the margin of safety
How is disinfection valuable?
It has the ability to kill or inhibit microorganisms in situations where sterilisation procedures cannot be applied
give examples of situations where sterilisation techniques cannot be applied
cant be applied to skin, or equipment that requires frequent cleaning but would be damaged by heat
What does the effectiveness of a disinfection procedure depend on?
Species of contaminating organisms (especially if spore producing) And the quantity of organisms
Particular chemical used, and the concentration of the chemical
Length of exposure to the chemical
Amount of organic material present (e.g. soil, faeces, blood)
The type and condition of the material to be disinfected.
What is the purpose of streaking Staph. Aureus colonies on MS agar plate?
the high salt content of MS agar makes it selective for staphylococci
What is the growth of s. aureus indicated by?
Yellow colour (this is the acid produced by the S. aureus during the fermentation of mannitol changes a pH indicator in the medium to yellow)
what is the thermal death point?
the temperature at whch all bacterial cells in standard suspension will be killed if maintained at that temperature for 10 mins
what is standard suspension?
5 x 10 ^8 organisms
