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
