Control of microbes Flashcards
what are the 5 methods of heat sterilisation?
pasteurisation disinfection dry heat autoclaving (moist heat) freezing/fridge
what is pasteurisation?
For foods in liquid form e.g. milk - it preserves it whilst maintaining taste and texture. It also reduces microbial growth
what are the ways of pasteurisation and their conditions
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
what is disinfection?
Apply temps below that of sterilisation - it does not constitute sterilisation and many bacterial spores are not killed by this! but it does work
what is dry heat?
uses higher temps and longer exposure. It oxidises cell constituents and denatures proteins.
- Good for water sensitive materials
conditions for dry heat sterilisation
180 degrees, 30 min
160 degrees, 120 min
what is autoclaving?
effective against all types of microbes.
Proteins, nucleic acids and membranes denature more readily than dry heat.
conditions for general autoclaving
Saturated, pressurised steam -
121 degrees, 15 mins, 1 atm
134 degrees, 3 min, 2 atm
what are conditions of autoclaving to - sterilise media, and sterilise waste with solidmateiral
121 degrees, 15 psi…
20 min for sterilise media
40 min for sterilise waste with solid material
what are autoclaving conditions for clinical contaminant level III waste?
135 degrees ,15 psi, 30-60 mins
what does refrigeration do?
slows microbial growth and production. BUT there are still some microbes that can grow slowly at 4-8 degrees - listeria (food poisoning)
what does freezing do?
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
What are the 2 types of radiation sterilisation?
- Non ionising
2. Ionising
what is non ionising radiation for sterilisation?
UV rays used to reduce airborne pathogen counts e.g in surgical theatres, and disinfect smooth surfaces
What is ionising radiation for sterilisation?
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
what is filtration?
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
what do we filter?
Filter the air e.g surgical masks
Name 6 chemical methods of sterilisation
- Ethylene oxide
- Aldehydes
- Alcohols
- Phenols
- halogens
- oxidants and surfactants
what are the physical methods of sterilisation and describe
Heat - cheap, good at killing pathogens
Radiation - expensive, only specialised conditions
filtration - inexpensive but not really used
How is ethylene oxide used ?
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
How are aldehydes used ?
(formaldehyde) - disinfection. water soluble gas - germicide for bacteria, fungi & viruses.
- At higher concs it can kill spores
- mode of action is by protein denaturation
How are alcohols used ?
e.g ethanol, propanol Bacteria and fungi but NOT viruses. DONT kill bacterial spores Denatures proteins and dissolves membranes. - Surgical, hands, skin
How are phenols used ?
used in labs and hospitals.
Denatures proteins and disrupts membranes.
Has some performance against spores & viruses.
e.g trilosan sanitizier - bactericidal
how are halogens used?
Microbicidal and kills spores. - disinfectants
Chlorine - denatures proteins by binding to free amino groups
Iodine - disinfect skin and wounds = germicides
