Sterilisation Flashcards
How do we control microbes
Either kill or remove microbes
What are sterilisation and disinfection used for
Controlling microbes and their are physical and chemical methods
What is sterilisation
Absolute term. All living material is destroyed or removed from an object
What is disinfection
The killing, inhibition, or removal of all microorganisms likely to cause disease. Chemical agents, antiseptic (wound antiseptic compounds) and chemical agents suitable on living tissue as selective toxicity and less toxic than disinfectants
What is sanitation
Reduction of microbial population to a safe level in line with public health standards. A system like this accepts it isn’t always possible or desirable to kill all organisms and reducing numbers may be all that is needed
When is a sample only sterile
If one chance in a million that a live microbe is present
What are the general principles of microbial activity
When there are fewer organisms present, shorter time needed to sterilise, cleaning objects before sterilising improves efficiency, tissue and blood can impair chemical agents, microbes differ in their susceptibility to antimicrobial agents, they are more susceptible in active growth, rate and amount of killing is only meaningful under defined conditions, environmental factors influence killing e.g temperature, population size and composition
What are osmotic effects
Very high salt or sugar content so water has to leave
What factors effect bacterial growth
Availability of nutrients and water, temperature, atmosphere, radiation, mechanical and sonic stress and moisture and drying
What are the physical methods of sterilisation
Heat, filtration and radiation
What is moist heat?
Water vapour is present and moist heat kills by disrupting membranes and denaturing proteins and interfering with H bonding
What are autoclaves used for?
Sterilisation
Why does moist heat require Lower temps than dry heat
As no water or steam is involved
What is the cell and spore killing time for yeasts
Cell 5 min at 50-60 spore 5 mins at 70-80
What is the cell and spore killing time for moulds
Cell 30 min at 62 and spore is 30 min at 80
What is the cell and spore killing time for bacteria
Cell 10 min at 60-70 and spore is 2-800 min at 100
What is the cell killing time for viruses
Cell is 30 min at 60
If something is to be sterilised then….
All spores must be killed
How do we raise the boiling point of water
We increase pressure
Describe the autoclave
121 degrees at 15 mins at 15 psi (pounds per square inch) it kills everything except extreme thermophiles and is widely used and cheap. Increased pressure allows water to reach 121. But many materials are destroyed at high temps
What is the autoclave used in
The canning industry and Tyndalisstion, which is used in food storage and is fractional sterilisation that involves boiling goods in cans or jar for 20 mins a day, 3 days in a row
Do we need to sterilise medical devices
Yes
Do we need to sterilise food preservatives
No
What is bacteriostatic
Stops growth eg tetracycline
What is bactericidal
It kills growth eg rifampin
What is decimal reduction time
The time taken under defined conditions to reduce a population by 90%
It is written as Dtemp = x min - D121. : 2 min
What is the D value
Under distinct conditions where we achieve 90% or organism reductions
What is a pasteurisation
Use of mild heat to reduce microbial population and is effective on most pathogens. Mycobacterium bovis has current problems and one of 3 species contributing to TB brucellosis abortus cause brucellosis in cattle
How does dry heat kill
160 degrees for 2 hours or 170 degrees for 1 hour and only used on materials that won’t melt and kills by oxidation- combustion- add oxygen to it to burn it
What is batch pasteurisation
Original method and heat to 66 degrees for 30 mins
What is flash pasteurisation
Heat to 71 degrees for 15 seconds then a rapid cool down
What is UHT
Ultra high temp treatment - 141 degrees for 2 seconds and stored at room temp
What is an issue with high temps
Always risk denaturing the proteins and the benefits of the organic product
describe filtration
exclusion- you remove, microbes behave as particles so can be physcially removed from liquids and gases. Air filters and HEPA filters
what are membrane filters
trapping of microbes on a surface level. Thin membranes with a defined pore size and membrane are composed of various plymers
what else are membrne filters used for
sampling large volumes of liquid, and can support the growth of bacteria when overlaind onto a growth media
what are the problems with filters
anything you filter you can clog, due to dirty suspensions and this is fixed with a series of filters and pre-filters where the first one is replaced when it clogs up
what are the steps for water sampling with membrane filters
Filter the water sample, Remove the membrane from the filter, Place the membrane on nutrient medium and Incubate and count the colonies
what is UV radiation used for and when is it most useful
260 nm is the most useful and it destroys bacteria and damages DNA
What is the function of radiation
it creates reactive species, affects DNA, proteins and lipids
What are the types of radiation
It can be ultraviolet, visible and infrared. Gamma, X-rays, UV, (most harmful) visible, infrared and radio waves. The higher the energy in the radiation, the greater the biological effect
Describe gamma rays
in the range of 10-2 and 10 -5 are most useful
lethal to bacteria, oxidising effects and generation of reactive o species
has good penetration and useful for the sterilisation of packaged goods e.g syringes and useful for the sterilisation and disinfection of packaged foods- kills bacteria that causes food poisioning
what happens in bacteriocidal and fungicidal
the organism is killed
what happens in bacteriolytic
organism is killed and membranes are disrupted
what happens in bacteriostatic and fungistatic
growth is inhibited
when does growth resume
when the agent is removed
what activity do many antibiotics have
bacteriostatic activity
what concentration does bacterialcidal have
high concentration
what concentrtion does bacteriostatic have
low concentration
what are phenolics
chemical agents
what are the adantages of chemcial agents
works in dirty solutions, long lasting and kills mycobacterium tuberculosis
what are the disadvantages of chemical agents
toxicity and cumulative (dangerous in the environment) and suitable as a surface disinfectant only
what is used to compare the strength of different disinfectants
MIC- Minimum inhibitory concentration= the smallest amount needed to inhibit growth. Looks into the nature of organisms, concentration of organism, incubation time, temp and pH
