Control of microbes

Question 1

what are the 5 methods of heat sterilisation?

Answer 1

pasteurisation
disinfection
dry heat 
autoclaving (moist heat)
freezing/fridge

Question 2

what is pasteurisation?

Answer 2

For foods in liquid form e.g. milk - it preserves it whilst maintaining taste and texture. It also reduces microbial growth

Question 3

what are the ways of pasteurisation and their conditions

Answer 3

Low temp - 61.5 degrees, 30 min
Flash - 71 degrees, 15 sec
High temp - 80-85 degrees, 5-10 secs
UHT - 150 degrees, 2.5 secs

Question 4

what is disinfection?

Answer 4

Apply temps below that of sterilisation - it does not constitute sterilisation and many bacterial spores are not killed by this! but it does work

Question 5

what is dry heat?

Answer 5

uses higher temps and longer exposure. It oxidises cell constituents and denatures proteins.
- Good for water sensitive materials

Question 6

conditions for dry heat sterilisation

Answer 6

180 degrees, 30 min

160 degrees, 120 min

Question 7

what is autoclaving?

Answer 7

effective against all types of microbes.

Proteins, nucleic acids and membranes denature more readily than dry heat.

Question 8

conditions for general autoclaving

Answer 8

Saturated, pressurised steam -
121 degrees, 15 mins, 1 atm
134 degrees, 3 min, 2 atm

Question 9

what are conditions of autoclaving to - sterilise media, and sterilise waste with solidmateiral

Answer 9

121 degrees, 15 psi…
20 min for sterilise media
40 min for sterilise waste with solid material

Question 10

what are autoclaving conditions for clinical contaminant level III waste?

Answer 10

135 degrees ,15 psi, 30-60 mins

Question 11

what does refrigeration do?

Answer 11

slows microbial growth and production. BUT there are still some microbes that can grow slowly at 4-8 degrees - listeria (food poisoning)

Question 12

what does freezing do?

Answer 12

used for storage of bacteria -80 degrees.
Can also use glycerol to prevent the formation of crystals because ice crystals can disrupt membranes which can kill some microorganisms

Question 13

What are the 2 types of radiation sterilisation?

Answer 13

1. Non ionising

2. Ionising

Question 14

what is non ionising radiation for sterilisation?

Answer 14

UV rays used to reduce airborne pathogen counts e.g in surgical theatres, and disinfect smooth surfaces

Question 15

What is ionising radiation for sterilisation?

Answer 15

It penetrates deep and destroys bacterial endospores.
(gamma and corpuscular) - used to sterilise bandages, suture, plastic medical items and heat sensitive pharmaceutics.
Dose depends on the level of contamination (bioburden) and how sensitive the microbes are to radiation

Question 16

what is filtration?

Answer 16

Heat sensitive, liquids & gases.

• Most only catch bacteria and fungi, but ultra fine can filter viruses and large molecules.
• Membrane filters made out of organic colloids

Question 17

what do we filter?

Answer 17

Filter the air e.g surgical masks

Question 18

Name 6 chemical methods of sterilisation

Answer 18

1. Ethylene oxide
2. Aldehydes
3. Alcohols
4. Phenols
5. halogens
6. oxidants and surfactants

Question 19

what are the physical methods of sterilisation and describe

Answer 19

Heat - cheap, good at killing pathogens
Radiation - expensive, only specialised conditions
filtration - inexpensive but not really used

Question 20

How is ethylene oxide used ?

Answer 20

its a very reactive gas - toxic.

Low temp 20-60 degrees and high penetration capacity, BUT, can’t kill dried organisms and needs 90% humidity

Question 21

How are aldehydes used ?

Answer 21

(formaldehyde) - disinfection. water soluble gas - germicide for bacteria, fungi & viruses.
- At higher concs it can kill spores
- mode of action is by protein denaturation

Question 22

How are alcohols used ?

Answer 22

e.g ethanol, propanol
Bacteria and fungi but NOT viruses. 
DONT kill bacterial spores 
Denatures proteins and dissolves membranes. 
- Surgical, hands, skin

Question 23

How are phenols used ?

Answer 23

used in labs and hospitals.
Denatures proteins and disrupts membranes.
Has some performance against spores & viruses.
e.g trilosan sanitizier - bactericidal

Question 24

how are halogens used?

Answer 24

Microbicidal and kills spores. - disinfectants
Chlorine - denatures proteins by binding to free amino groups
Iodine - disinfect skin and wounds = germicides

Question 25

how are oxidants and surfactants used?

Answer 25

Oxidants e.g Hydrogen peroxide - antiseptics for skin, wounds, mucosa

Surfactants - moderate bactericidal.
Mainly bacteria and fungi But only effective on gram positive, not gram negative rods.

No effect on tuberculosis bacteria, spores, non encapsulated viruses.

Question 26

what are advantages of surfactants?

Answer 26

Low toxicity, no odor, good on skin, cleaning