Controlling contamination Flashcards
contam of medicals intro to sterilisation moist heat other techniques controlling processes Calculations sources of contam disinfectants
What are the 4 medical relevencies of biofilms?
Majority of infections involve cells growing in biofilms
Indwelling medical devices
Growth on surfaces in e.g hospitals
Biological liquid systems (e.g. dialysis equipment)
What is bacterial sporulation?
Survival strategy when nutrients become exhausted
Mechanism used by some Gram-positive bacteria
Spores are very resistant to heat, radiation, desiccation and chemical agents
Can survive for many years
What are the two main consequences of microbial contamination?
- Health hazard
Contaminating organism or its toxins can cause disease - Spoilage
Therapeutic breakdown of actives, or another component of formulation
Might lose aesthetic appeal →Non compliance
What are the 8 classes of agents used as preservatives in the UK?
Organic acids
Parabens
Aromatic alcohols
Substituted alcohols
Biguanides
Mercurials
Substituted phenolic agents
Quaternary ammonium compounds
Which are the 2 preservatives used in oral products?
Organic acids
Parabens
Why are organic acids and esters preferred?
Organic acids
- limited by pH dependence;
- work at pH values up to pKa
Parabens
- overcome pH dependence of organic acids
- Active at low concentrations.
- Non toxic, cheap, stable.
- Reasonable spectrum of activity
- bactericidal, fungicidal (not sporicidal)
- Physically undetectable
How are preservatives evaluated?
- suspension test
- criteria of acceptance
What are the 5 factors affecting choice of any preservative?
- Intended application
- No. & type micro-orgs present
- Safety, stability & Cost
- Micro-environment
- Properties of chemical agent
What are the two sterility probablities?
Sterility Assurance Level (SAL)
Probability of a Non-Sterile Unit (PNSU)
What is the minimum standard PSNU required?
For most pharmaceutical products, the minimal required standard is a PNSU of 1 in 106
What are the three sterilisation processes?
Destruction - e.g. flaming, chemical oxidation
- not practical for pharmaceutical products
Killing/inactivation
- used in most official methods
- may not remove endotoxins
Removing
- filtration, centrifugation
What is moist heat sterilisation?
Involves steam, usually at 121-134C
Very effective
Widespread application
Used for dressings etcs
What is dry heat sterilisation?
Usually in the range of 160-180oC
Less effective than moist heat sterilisation
Used for glass and metals etc
What is radiation sterilisation?
Sterilisation using gamma rays, accelerated electrons, X rays or UV
Alternative method for heat-sensitive products
Mainly for articles in dried state, e.g. plastic syringes, dry pharmaceutical products etc.
What is gaseous sterilisation?
Uses ethylene oxide or formaldehyde
Not same sterility assurance as heat - only used for heat sensitive items
Mainly for reusable surgical instruments, medical/diagnostic equipment, surface sterilisation of powders
What is filtration?
For sterilisation: 0.2-0.22µm filters used
The only process that removes microorganisms
Also used for removal of particulates, both from gases and liquids
For heat sensitive injections, ophthalmic preparations, biological products, and air and other gases for supply to aseptic areas
Which 4 factors used to choose sterilisation?
- stability and nature of product
- scale of production
- type and level of contamination
- cost
What is the D value?
decimal reduction time: time needed to reduce population by a factor of 10
t2 - t1
———–
logN1 - logN2
What is the Z value?
increase in temperature needed to reduce the D-value 10 fold
T2 - T1
———–
logD1 - logD2
What is autoclaving?
Moist heat with temp >100oC can only be achieved under pressure
Performed in autoclave - similar to domestic pressure cooker, but better facilities for control
Organisms killed by combination of
- temperature
- hydration
- time
What are the three types of steam?
- Superheated steam is water in the vapour phase and behaves like a gas. If the temperature decreases, the pressure decreases
- Supersaturated steam or wet steam is in liquid phase and is made up of small droplets of water held in suspension by convection currents
- Dry saturated steam exists on the phase boundary. If you lower the temperature it will condense
What the two types of heat?
- Sensible heat: when exchanged, results in change of temperature
- Latent heat: when exchanged, results in change of physical state - there is no temperature change
What are the two types of autoclaves?
Portable bench-top sterilisers
- design is similar to domestic pressure cooker
Large scale sterilisers
- gravity displacement autoclave
- porous load autoclave (vacuum-assisted)
What is air ballasting?
Sterile fluids may be packaged in flexible plastic containers (e.g. IV fluids)
Pressure in airspace above fluid may lead to bursting
to prevent this, some air may be retained to create overpressure in specifically designed autoclaves
To prevent layering of air, such autoclaves may require fan or spraying mechanism to mix air and steam
What are the three effects of air in the autoclave?
- Unjacketed bench autoclave
Usually controlled by pressure only
Air leads to lower temperature - Jacketed autoclave
Both pressure and temperature controlled
Air can lead to superheating - Layering
Density of air = ~2 x density of steam
Air forms layer in any container in upright position
Air will be cooler
What are the 4 uses of dry heat sterilisation?
Substances that can’t be subjected to moisture
- Water soluble powders (thermostable)
Materials not penetrable by steam
- Oils, fats, waxes, dry items enclosed in sealed container etc.
Glassware
- Glass vessels, ampoules, syringes etc.
Metal surgical instruments
- Scalpels, forceps etc
