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Microbiology > Sterilisation > Flashcards

Sterilisation Flashcards

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Biology 101 flashcards
1
Q

How do we control microbes

A

Either kill or remove microbes

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2
Q

What are sterilisation and disinfection used for

A

Controlling microbes and their are physical and chemical methods

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3
Q

What is sterilisation

A

Absolute term. All living material is destroyed or removed from an object

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4
Q

What is disinfection

A

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

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5
Q

What is sanitation

A

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

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6
Q

When is a sample only sterile

A

If one chance in a million that a live microbe is present

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7
Q

What are the general principles of microbial activity

A

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

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8
Q

What are osmotic effects

A

Very high salt or sugar content so water has to leave

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9
Q

What factors effect bacterial growth

A

Availability of nutrients and water, temperature, atmosphere, radiation, mechanical and sonic stress and moisture and drying

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10
Q

What are the physical methods of sterilisation

A

Heat, filtration and radiation

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11
Q

What is moist heat?

A

Water vapour is present and moist heat kills by disrupting membranes and denaturing proteins and interfering with H bonding

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12
Q

What are autoclaves used for?

A

Sterilisation

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13
Q

Why does moist heat require Lower temps than dry heat

A

As no water or steam is involved

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14
Q

What is the cell and spore killing time for yeasts

A

Cell 5 min at 50-60 spore 5 mins at 70-80

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15
Q

What is the cell and spore killing time for moulds

A

Cell 30 min at 62 and spore is 30 min at 80

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16
Q

What is the cell and spore killing time for bacteria

A

Cell 10 min at 60-70 and spore is 2-800 min at 100

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17
Q

What is the cell killing time for viruses

A

Cell is 30 min at 60

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18
Q

If something is to be sterilised then….

A

All spores must be killed

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19
Q

How do we raise the boiling point of water

A

We increase pressure

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20
Q

Describe the autoclave

A

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

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21
Q

What is the autoclave used in

A

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

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22
Q

Do we need to sterilise medical devices

A

Yes

23
Q

Do we need to sterilise food preservatives

A

No

24
Q

What is bacteriostatic

A

Stops growth eg tetracycline

25
Q

What is bactericidal

A

It kills growth eg rifampin

26
Q

What is decimal reduction time

A

The time taken under defined conditions to reduce a population by 90%
It is written as Dtemp = x min - D121. : 2 min

27
Q

What is the D value

A

Under distinct conditions where we achieve 90% or organism reductions

28
Q

What is a pasteurisation

A

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

29
Q

How does dry heat kill

A

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

30
Q

What is batch pasteurisation

A

Original method and heat to 66 degrees for 30 mins

31
Q

What is flash pasteurisation

A

Heat to 71 degrees for 15 seconds then a rapid cool down

32
Q

What is UHT

A

Ultra high temp treatment - 141 degrees for 2 seconds and stored at room temp

33
Q

What is an issue with high temps

A

Always risk denaturing the proteins and the benefits of the organic product

34
Q

describe filtration

A

exclusion- you remove, microbes behave as particles so can be physcially removed from liquids and gases. Air filters and HEPA filters

35
Q

what are membrane filters

A

trapping of microbes on a surface level. Thin membranes with a defined pore size and membrane are composed of various plymers

36
Q

what else are membrne filters used for

A

sampling large volumes of liquid, and can support the growth of bacteria when overlaind onto a growth media

37
Q

what are the problems with filters

A

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

38
Q

what are the steps for water sampling with membrane filters

A

Filter the water sample, Remove the membrane from the filter, Place the membrane on nutrient medium and Incubate and count the colonies

39
Q

what is UV radiation used for and when is it most useful

A

260 nm is the most useful and it destroys bacteria and damages DNA

40
Q

What is the function of radiation

A

it creates reactive species, affects DNA, proteins and lipids

41
Q

What are the types of radiation

A

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

42
Q

Describe gamma rays

A

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

43
Q

what happens in bacteriocidal and fungicidal

A

the organism is killed

44
Q

what happens in bacteriolytic

A

organism is killed and membranes are disrupted

45
Q

what happens in bacteriostatic and fungistatic

A

growth is inhibited

46
Q

when does growth resume

A

when the agent is removed

47
Q

what activity do many antibiotics have

A

bacteriostatic activity

48
Q

what concentration does bacterialcidal have

A

high concentration

49
Q

what concentrtion does bacteriostatic have

A

low concentration

50
Q

what are phenolics

A

chemical agents

51
Q

what are the adantages of chemcial agents

A

works in dirty solutions, long lasting and kills mycobacterium tuberculosis

52
Q

what are the disadvantages of chemical agents

A

toxicity and cumulative (dangerous in the environment) and suitable as a surface disinfectant only

53
Q

what is used to compare the strength of different disinfectants

A

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

Microbiology (29 decks)

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