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TW8 – Sterilisation and disinfection – 14th November



Definitions
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Disinfection: reduce numbers of microorganisms to such a low level that it is no
longer infectious
Cleaning: remove physical stuff (dirt/fats/proteins)
Antibacterial: anything that kills bacteria
...
(active form)
Endospore: An egg like structure that resides inside bacteria (dormant form)
Mycobacteria: gram +, pathogenic, aerobic, acid fast – causes of TB and Johne’s
disease (both bovine)


Disinfectants



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Overview
There are different types of disinfection level; low moderate and high
Many disinfection actions are inhibited by proteins and organic matter; so often
must clean (e
...
hot water) and then disinfect

Soap etc
...
heat
...

How it works
Seems to denature proteins within bacteria and kill them (bacteria)
Toxicity and activity: Propanol > ethanol
Effective on:
Fungi and mycobacterium
Only work on enveloped virus (envelop part of cell membrane)
Useless on:
Not effective against spores
Directions:
E coli – 10 – 70 seconds
Usually leave alcohols on surfaces for 5 mins then wipe off to destroy harder
bacteria
Can mix with HCl to decrease contact time and increase effectiveness
Positives:
Relatively inexpensive
Rarely cause skin irritation
Good on skin and surfaces
Negatives:
Highly flammable
Can cause rubbers and plastics to breakdown
If used a lot on skin can dry it out and cause irritation over longer term basis
Issues with drunks in hospitals: alcohol gels are methanol based, so have to treat
them for methanol poisoning with ethanol

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Cdif – usually lives in gut – kept under control by natural flora (it is a spore)
...
– using
alcohol gels in hospitals can promote Cdif bacteria to sporalate, creating issues
throughout hospitals

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Aldehydes
Pathology samples will be kept in to aldehydes – preserves samples
Currently one of most effective microbial

Composition:
Gaseous or liquid
(G) Formaldehyde bombs (to clean rooms)
(L) Glutaraldehyde (for medical equipment)
Formaldehyde – when there are spills in labs (especially cat
...
Prevents bacteria from re-growing for
about 12hrs
Activity:
Gram positive > gram neg
...
g
...
g
...
2 hyperchlorine aka 520000 parts per million of chlorine
Chlorine is active ingredient
Usually goes to 1 in 10 dilution with water
Need about 5000 parts per million of chlorine in water in household bleach
Must use 35% conc
...

Effective on
Good against vegetative bacteria
Good against spores and fungi – but over a prolonged period of time
Useless against
…
Negatives:
Relative unstable and break down quite rapidly so must be made up on a daily basis
Harmful to skin, eyes, lungs
If you mix bleach with another cleaner results in fumes (chlorine gas)
Chlorine gas makes lung over produce mucous and you drown (used in WW1)
Incompatible with metals - leads to corrosion
Can’t use bleach on equipment such as a centrifuge (made from milled aluminium or
steel) because it can corrode them and become very dangerous
Becomes inactive in the presence of organic material, e
...
blood, vomit etc
...

A 1% concentration is very effective
Is a pink substance that when left for 7 days turns clear and smells like chlorine –
which shows that it is inactive
They also change colour when they’ve had too much of a certain substance added
and it has deactivated it
...
)
Bacteria
Useless against:
…
Negatives:
Corrosive to zinc, copper and steel (don’t use on centrifuges)
Unstable even at low concentrations, pots will last for about a week
Positives:
Relatively safe – it can burn the skin and damage eyes – however it is readily broken
down in the environment (catalases) so after a few hours there isn’t much product
left on surfaces
Effective on hard surfaces
Very powerful, breaks down easily in the environment
Good for hospital cleaning
Relatively safe – it is an irritant in the powder form, not so much in liquid form
Phenols/clear phenols
Composition:
Hycogin was an old commonly used phenol disinfectant
How it works:
Improved by adding detergent – makes a good cleaner and detergent in one
Activity:
Not good with organic matter
Effective on:
Bacteria, mycobacteria, and fungi
Useless against:
Spores and lipids
Negatives:
Are reduced by organic matter
Can be absorbed by porous material, which can lead to discolouration

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Phenol are carcinogenic – a product called hycogin was the best, has been banned
...


-

Quants
Composition
Usually made up at 0
...

Useless against:
Spores
Positives:
Non toxic




Summary
Effective against

Spores
- Aldehydes
- Halogens (hypochlorites)
- Peroxygens
Bacteria
- Alcohol
- Halogens (hypochlorites)
- Halogens (iodine)
- Peroxygens
- Phenols
- Quants
Viruses
- Halogens (iodine)
- Peroxygens

Fungi
- Alcohol
- Halogens (hypochlorites)
- Halogens (iodine)
- Peroxygens
- Phenols
- Quants

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Useless against

Spores
- Alcohol
- Biguanides
- Halogens (iodine)
- Phenols
- Quants
Bacteria
- Biguanides
Viruses

Fungi

Lipids
- Quants




Inhibited by organic material
Biguanides - Halogens (hypochlorites) - Virkon (peroxygen) – Phenols/clear
phenols -



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