3. Sterilisation, Disinfection & FIltration Flashcards
1
Q
Terms:
- Sterile
- Sterilisation
- Sepsis
- Asepsis
- Aseptic technique
- Antiseptic
- Disinfectant
A
- Sterile – absence of living organisms
- Sterilisation – removal or destruction of all viable micro-organisms
- Sepsis – growth of micro-organisms in blood & other tissues
- Asepsis – any practice that prevents entry if infectious agents into sterile tissues (prevents infection)
- Aseptic technique – use of procedures in the preparation of sterile products which prevent the introduction of contaminants
- Antiseptic – chemical agents applied directly to exposed body surfaces (skin, mucous membranes), wounds & surgical incisions to prevent introduction of micro-organisms
- Disinfectant – chemical agents applied to inanimate objects (surfaces)
2
Q
Sterilisation
A
- Physical/chemical process that completely destroys or removes microbes including spores
- Used for surgical instruments, syringes
- E.g. Heat, irradiation, filtration
3
Q
Disinfection:
A
- Reduces the number of pathogens (but not spores) so they pose no threat of disease
- Chemical agents used in inanimate (surfaces) or animate (living tissue)
- E.g. Sodium hypochlorite (bleach), iodine, alcohols
4
Q
Sterile products: Certain pharmaceutical products must be sterile
A
- Inactivated in the GI tract - peptides, proteins, chemotherapeutic agents
- Enter body ‘sterile’ areas i.e. sterile organs - irrigation solutions, dialysis solutions
- Bypass the bodies defence mechanism (skin) - injections, eye drops, medical devices, sutures, surgical instruments
5
Q
Sterile products: Terminally sterilised in the final container
A
- Preferred method
- Not for heat sensitive products
- Fill & seal product under cleanroom conditions
- E.g. Heat or radiation
6
Q
Sterile products: Aseptic filling
A
- Drug substances unstable or packaging degraded with heat
- Contamination risks during formulation & filling greater
- Dosage form, final container & packaging sterilised separately
- E.g. Filtration 0.2 µm membrane
7
Q
Microbial death
A
- Death of whole population is not instantaneous (hard to detect)
- Begins when certain threshold of agent/process is reached
- Death continues in a logarithmic manner as the time/concentration is increased
- Active cells tend to die more quickly than less metabolically active cells
- Sterilisation occurs at a point at which survival of any cells is highly unlikely - absolute term
8
Q
Factors affecting microbial death rate
A
- Total # of micro organisms - higher load of contaminants takes longer to destroy
- Nature of the micro-organisms - usually a mixture of bacteria, fungi, spores
- Temperature & pH of the environment
- Concentration (dose or intensity) of agent
- Mode of agent - killing (bactericidal) or inhibiting (bacteristatic) the micro-organism
- Presence of solvents, organic matter & inhibitors - saliva, blood faeces can inhibit action of some disinfectants
9
Q
Mode of action: Cellular targets & antimicrobial agents
A
Cell wall: Chemicals, detergents, alcohols -> damages cell wall
Cell membrane: Detergents -> open cell membrane
Cellular synthesis/ [DNA/RNA]: Formaldehyde, radiation, ethylene oxide -> inhibits protein synthesis/[Mutation]
Proteins: Moist heat, alcohol, phenols -> denatures proteins/attaches to proteins
10
Q
Methods of sterilisation (3):
A
- Physical (thermal):
- Heat: Dry or moist - Physical (non-thermal):
- Radiation - gamma ray, UV
- Filtration - Chemical:
- Gaseous
- Liquid
11
Q
Dry heat (2):
A
- Dehydrates cell wall, denatures proteins
- Oxidises cells, burning them to ashes
- Temp ranges from 160 C to thousands of degrees
- Hot air oven:
- 150-180 C
- Bacillus atrophaeus is the biological indicator - Incineration:
- Bunsen burners - inoculating loops in lab
- Incinerators (800-6500 C) - destruction of hospital waste e.g. dressings, needles, cytotoxic materials
12
Q
Moist heat (3):
A
- Boiling - does not kill all resistant bacteria:
- Disinfection not sterilisation
- 100 C for 30 minutes
- At home - babies bottles, disinfect water - Pasteurisation of liquids:
- Inactivates most viruses & detsroys most bacteria
- 71.6 C for 15 secs or 63 - 66 C for 30 mins
- Does not kill spores or heat resistant microbes
- Used mainly in food industry e.g. milk - Tyndallisation:
- Intermittent sterilisation
- Items exposed to free-flowing steam for 30 - 60 minutes several times over 3 days
- Used for heat sensitive culture media, carbohydrates, come canned foods
13
Q
Moist heat - autoclave
A
- Steam under pressure
- Sterilisation
- At sea level normal atmospheric pressure is 15 psi:
+ Water will boil at 100 C
+ Steam will remain at this temperature
+ Too low to reliably kill all microbes
+ To raise temp of steam, pressure must be increased - Used for heat-resistant material:
+ Glassware, surgical dressings, metallic instruments, liquids, paper, media, some plastics
+ Ineffective for substances that repel water e.g. oils, or those that are harmed by it e.g. powders
+ Terminal sterilisation of aqueous injections, ophthalmic preparations, irrigation & haemodialysis solutions & equipment used in aseptic processes
+ 121 C for 15 minutes - Air in chamber is evacuated with saturated steam
- Item completely surrounded by steam which on contact condenses to release its latent heat
14
Q
Advantages & disadvantages of most heat - autoclave
A
Advantages:
- Temps are < 100 C so that spores are killed
- Condensation of steam generates extra heat
- Condensation also allows steam to penetrate into porous materials
- Most reliable method, non-toxic, cheap & easy to monitor
Disadvantages:
- Proper loading is critical - all items must have contact with steam
- Items should be free from grease & oil
- Explosive
15
Q
Autoclave - monitoring (3):
A
- Physical - use of an internal thermocouple to accurately measure the temp cycle
- Chemical - heat sensitive chemical that changes colour at the correct temperature & exposure time (autoclave tape)
- Biological - spore-forming organism is added & later cultured to ensure it has been killed (Bacillus stearothermophilus)
16
Q
Microbial control methods - physical (HEAT) summary
A
Dry oven:
- Sterilisation
Moist:
- Steam under pressure: Sterilisation
- Boiling water: Disinfection
17
Q
Radiation:
A
Energy emitted from atomic activities at high velocities through matter or space
- Penetrates liquids & most solid materials
- Used for some foods (with no ill effects)
- Drugs, vaccines, medical instruments (especially plastics), syringes, gloves, implants e.g. heart valves
18
Q
Radiation: Gamma rays
A
- Cobalt 60 or Caesium 137 radionuclides
- Used in industrial facilities for dry pharmaceutical or heat-liable product containers
- High penetration with only small rise in heat
- High volume loads
19
Q
Radiation: UV
A
- Disinfection rather than sterilisation - not as penetrating
- 200 nm most effective wavelength
- Used to disinfect air or surfaces - LAFC, hospital rooms, operating rooms
20
Q
Microbial control methods - physical (RADIATION) summary
A
Gamma ray: Sterilisation
UV: Disinfection
21
Q
Filtration
A
- Removes micro-organisms from air or liquids
- Fluid strained through a filter membrane with openings large enough for the fluid to pass but too small for micro-organisms
- Membranes made of cellulose acetate, polycarbonate & plastics whose pore size is carefully controlled
- For products that cannot be heat sterilised - serum, blood products, drugs, IV fluids, media
- Water purification - doesn’t remove water soluble toxins that cause disease
- Sterilising filter - 0.22 µm
- Reusable, sterilisable
22
Q
Filtration - air
A
Efficient means or removing airborne contaminants:
- HEPA filters used in pharmacy aseptic units & cabinets, operating rooms
- Cabinets or walls
23
Q
Filtration - liquids
A
- Screen filters - involve sieving out contaminants (micro-organisms or particles)
- Differing membrane sizes & size is not absolute
+ 0.16 - 0.388 µm
+ Virus will not pass through
24
Q
Filters used in aseptic compounding (2):
A
- FIlter needles:
- Single use disposable
- 5 µm pore size filter in hub
- NOT STERILSING pore size
- FIlters out only large particles
- Rubber, glass - Filter units:
- Single use disposable
- Various pore sizes - 0.22 µm, 0.45 µm
- 0.22 µm is a sterilising filter size
- Virus will pass through
25
Microbial control methods - physical (FILTRATION) summary
Air: Disinfection
Liquids: Sterilisation
26
Chemical sterilisation
Gaseous or liquid states:
| - Disinfectants & antiseptics
27
Chemical sterilisation - desirable qualities
- Rapid action - even at low concentrations
- Soluble in water or alcohol with long term stability
- Broad spectrum of activity with no human or animal toxicity
- Able to penetrate inanimate surfaces to sustain action
- Resistant to inactivation in presence of organic matter
- Non-corrosive & non-staining
- Affordable & readily available
NO CHEMICAL CAN DO ALL THIS!
- Glutaraldehyde & hydrogen peroxide come close
28
Chemical sterilisation: Gaseous
Ethylene oxide (EO):
- Colourless, flammable, explosive & toxic gas
- Prevents normal cellular metabolism & replication
- High-level disinfection
- Processing cycles overnight or longer
- Bacillus atrophaeus is the biological indicator
- Used for heat or moisture sensitive items e.g. gloves/plastics
29
Chemical sterilisation: Gaseous
| - Advantages & Disadvantages
Advantages:
- Items not damaged by heat or moisture, not corrosive
- Penetrates porous materials then dissipates well
Disadvantages:
- Expensive
- Toxic
- Longer process (dissipation longer)
- Explosive
30
Chemical sterilisation: Liquid
Factors affecting activity:
- Nature of micro-organism being treated
- Degree of contamination
- Time of exposure
- Strength of chemical action
- Composition of items being treated
Level of disinfection:
- High-level
- Intermediate-level
- Low-level
Composition of items:
- Smooth, solid items, more reliably disinfected than porous
- Organic matter can affect penetration - items must first be cleaned before disinfectants used
Time of exposure:
- Depends on micro-organisms & concentration of chemical
+ Neissera gonorrhoeae on H2O2 = 0.3 s
+ Influenza virus EO gas = 25 hours
Concentration of chemicals:
- Dilution expressed as ratio - chemical to solvent e.g. 200:1
- Parts per million - very dilute solutions e.g. chlorine 100 ppm
- Percentage - chemical added to water by weight or volume e.g. 70% isopropyl alcohol is also 30% water
31
Level of disinfection (3):
1. High level:
- Active against vegetative bacteria, viruses, fungi & mycobacteria - some activity against spores
- Used to disinfect heat-sensitive, critical devices e.g. endoscopes
- E.g. Aldehydes & hydrogen peroxide
2. Intermediate level:
- Active against micro-organisms above but not viruses or spores
3. Low level:
- Active only against SOME of the above micro-organisms
- E.g. Hand washing with unmedicated soaps
32
Chemical categories
- Biguanides
- Halogens
- Alcohols
- QACs
- Hydrogen peroxide
- Aldehydes
- [Phenolics]
- [Heavy metals]
- [Dyes]
- [Acids & Alkalis]
33
Chemicals - Biguanides
- Chlorohexidine
- Targets bacterial membrane & denatures proteins
- Low-to intermediate-level disinfectant active against most bacteria, fungi & some viruses
- Used as skin preparation prior to surgery:
+ Mild, low toxicity, rapid action
+ Hand scrubs
+ Can be diluted with alcohol
+ Inactivated by organic matter & soap
34
Chemicals - Chlorine
Sodium hypochlorite (bleach):
- Low-to high level at concentrations 100 - 5000 ppm
- Broad spectrum of activity (kills spores slowly) but inactivated by organic matter
- Combines with water & releases hypochlorous acid (HOCl) which denatures enzymes
- Disinfects floors, walls, bench tops, laundry, drinking water, decontaminate blood spills
- May bleach skin & corrode metal e.g. instruments
- Solutions are unstable & need to be prepared fresh (every 24 hours) - avoid sunlight
- Requires direct contact
- Affected by temp & pH of water
35
Chemicals - Iodine
Iodophor (povidone iodine)
- Low-level (concentrations 30-50 ppm free iodine)
- Broad spectrum of activity (kills spores slowly) but inactivated by organic matter
- Penetrates cell wall quickly to disrupt protein synthesis
- Non-irritant but stains clothes, toxic when absorbed
- Used for disinfecting medical equipment but mainly used as an antiseptic on wounds or handwashing
- 2% iodine used as
36
Chemicals - alcohols
Isopropyl alcohol (ethyl alcohol):
- Low to immediate-level
- Rapidly bactericidal (2 minutes) - denatures proteins through dehydration but NOT viruses
- Optimum concentration is 70%
- Used to disinfect surfaces e.g. necks of ampoules, rubber septa of vials, benches, trolleys
- Combined with other disinfectants for skin preparations e.g. chlorohexidine, hand rubs
- Flammable, inexpensive, & readily available, filterable, low cost
- Irritant to mucous membranes, inactivated by organic matter
37
Chemicals - Quaternary ammonium compounds (QACs)
QACs:
- Low level disinfection
- Acts as surfactants that alter membrane permeability of some bacteria & fungi
- Mild, low toxicity
- Used in 'medicated' hand soaps to wash away bacteria with skin cells
- Removes both 'bad' & 'good' bacteria
- Resistance can build up
- E.g. Benzylalkonium chloride, cetrimide
38
Chemicals - hydrogen peroxide
- Antiseptic at low concs
- Strong solutions are sporadical
- Damages proteins & DNA
+ Decomposes to oxygen & water
+ Releases free radicals
39
Chemicals - Aldehydes
- High level disinfection
- Kills spores & most other micro-organisms
- Disrupts activity of cellular enzymes & proteins
- Used to sterilise respiratory equipment, scopes, kidney dialysis machines, dental equipment
- Avoid wet surfaces & organic matters
- Glutaraldehyde is unstable especially with increase in pH
- Formaldehyde is extremely toxic & irritating to skin & mucous membranes
40
Chemical - others
- Phenolics - Tricloslan (may be toxic)
- Heavy metals:
+ Silver, copper, gold
+ Jewellery, hospital surfaces
- Dyes:
+ Aniline dyes active against Gram positive bacteria & some fungi
+ Very low-level, narrow spectrum of activity
+ Wound treatment
- Acids & alkalis:
+ Very low-level
+ White vinegar, acetic acid, lactic acid
41
Microbial control methods - physical (CHEMICAL) summary
Gases:
- Sterilisation
- Disinfection
Liquids:
- On animate objects: Antisepsis
- On inanimate objects: Sterilisation + Disinfection
