Microbiology Lecture 7 Flashcards
Define sterilisation.
Killing of all viable organisms, including endospores.
Define disinfection. Does it kill endospores?
Killing of all vegetative microbes. Typically doesnt kill endospores.
High level disinfection may kill endospores.
What is the most important environmental factor in microbe growth?
Temperature.
Do all microbes grow poorly in cold temperatures?
No, some grow well at 4*C, refrigerated foods are particularly susceptible to them.
What temperature foods should pregnant women avoid and why?
Cold foods, some bacteria grow well in cold conditions, and these foods are susceptible to their growth.
Define pasteurisation.
71*C for 15 seconds.
Define tyndallisation.
80*C on 3 successive days.
BDfine boiling.
100*C.
Define hot air oven temperatures.
160-180*C
Define incineration temperatures.
> 800*C.
Define autoclaving.
Steam at >100*C, pressurised.
What is superior for sterilisation, hot air oven, or autoclaving, and why?
Autoclaving, despite higher temperatures in the oven. This is because water is a better conductor of heat versus air.
Does boiling sterilise water?
No, boiling doesnt kill endospores. May also cause the release of endotoxins from appropriate bacteria like gram negative.
What temperatures can endospores resist up to? Are they susceptible to UV light and chemical disinfectants?
Up to 150*C. Resistant to UV light and most chemical disinfectants.
Where are endospores commonly found?
Soil.
What method is used to kill endospores, at what temperatures, and for how long?
Typically 121*C for 10-15 minutes.
What is especially important when autoclaving regarding the presence of air?
Some items wont sterilise properly as they may have trapped air pockets. Air must be allowed to flush out for correct sterilisation.
Define precleaning, and why itsimportant.
Precleaning is the removal of visible soiling from items to be autoclaved. This is so that the item may have full contact with the pressurised steam, so it can reach high enough temperatures and be sterile.
Define decimal reduction time.
Time required for a 10-fold reduction in viable cells - 90% dead.
What kind of curve does the decimal reduction time exhibit? How is it manipulated?
Exponential - logged to linearise for accurate extrapolation.
Give an example of decimal reduction time beginning with 1k microbes, and microbe count per minute, until 99.9% chance of death.
0 minutes - 1k 1 minute - 100 2 minutes - 10 3 minutes - 1 4 minutes - 0.1 5 minutes - 0.01 6 minutes - 0.001
In practice, what chance of death of all microbes is needed? Give both the decimal form and the scientific notation required.
99.9999% or 0.000001 - 10^-6 on the curve.
What are the three checks that can be done to assess correct autoclaving?
Printout of the cycle - physical check
Heat sensitive paper/tape - chemical
Spore test - biological
How often should a spore test for correct autoclave function be performed?
Once weekly.
