Sterilisation

Question 1

How do we control microbes

Answer 1

Either kill or remove microbes

Question 2

What are sterilisation and disinfection used for

Answer 2

Controlling microbes and their are physical and chemical methods

Question 3

What is sterilisation

Answer 3

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

Question 4

What is disinfection

Answer 4

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

Question 5

What is sanitation

Answer 5

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

Question 6

When is a sample only sterile

Answer 6

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

Question 7

What are the general principles of microbial activity

Answer 7

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

Question 8

What are osmotic effects

Answer 8

Very high salt or sugar content so water has to leave

Question 9

What factors effect bacterial growth

Answer 9

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

Question 10

What are the physical methods of sterilisation

Answer 10

Heat, filtration and radiation

Question 11

What is moist heat?

Answer 11

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

Question 12

What are autoclaves used for?

Answer 12

Sterilisation

Question 13

Why does moist heat require Lower temps than dry heat

Answer 13

As no water or steam is involved

Question 14

What is the cell and spore killing time for yeasts

Answer 14

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

Question 15

What is the cell and spore killing time for moulds

Answer 15

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

Question 16

What is the cell and spore killing time for bacteria

Answer 16

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

Question 17

What is the cell killing time for viruses

Answer 17

Cell is 30 min at 60

Question 18

If something is to be sterilised then….

Answer 18

All spores must be killed

Question 19

How do we raise the boiling point of water

Answer 19

We increase pressure

Question 20

Describe the autoclave

Answer 20

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

Question 21

What is the autoclave used in

Answer 21

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

Question 22

Do we need to sterilise medical devices

Answer 22

Yes

Question 23

Do we need to sterilise food preservatives

Answer 23

No

Question 24

What is bacteriostatic

Answer 24

Stops growth eg tetracycline

Question 25

What is bactericidal

Answer 25

It kills growth eg rifampin

Question 26

What is decimal reduction time

Answer 26

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

Question 27

What is the D value

Answer 27

Under distinct conditions where we achieve 90% or organism reductions

Question 28

What is a pasteurisation

Answer 28

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

Question 29

How does dry heat kill

Answer 29

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

Question 30

What is batch pasteurisation

Answer 30

Original method and heat to 66 degrees for 30 mins

Question 31

What is flash pasteurisation

Answer 31

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

Question 32

What is UHT

Answer 32

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

Question 33

What is an issue with high temps

Answer 33

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

Question 34

describe filtration

Answer 34

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

Question 35

what are membrane filters

Answer 35

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

Question 36

what else are membrne filters used for

Answer 36

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

Question 37

what are the problems with filters

Answer 37

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

Question 38

what are the steps for water sampling with membrane filters

Answer 38

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

Question 39

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

Answer 39

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

Question 40

What is the function of radiation

Answer 40

it creates reactive species, affects DNA, proteins and lipids

Question 41

What are the types of radiation

Answer 41

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

Question 42

Describe gamma rays

Answer 42

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

Question 43

what happens in bacteriocidal and fungicidal

Answer 43

the organism is killed

Question 44

what happens in bacteriolytic

Answer 44

organism is killed and membranes are disrupted

Question 45

what happens in bacteriostatic and fungistatic

Answer 45

growth is inhibited

Question 46

when does growth resume

Answer 46

when the agent is removed

Question 47

what activity do many antibiotics have

Answer 47

bacteriostatic activity

Question 48

what concentration does bacterialcidal have

Answer 48

high concentration

Question 49

what concentrtion does bacteriostatic have

Answer 49

low concentration

Question 50

what are phenolics

Answer 50

chemical agents

Question 51

what are the adantages of chemcial agents

Answer 51

works in dirty solutions, long lasting and kills mycobacterium tuberculosis

Question 52

what are the disadvantages of chemical agents

Answer 52

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

Question 53

what is used to compare the strength of different disinfectants

Answer 53

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