Lecture 1, 2, 3 Sterilisation and Disinfection Flashcards
What is sterilisation
Complete elimination or destruction of all forms of life
What is disinfection
Reduces or eliminates most microbes but not spores or other resistant bacteria, fungi or viruses
What is disinfectant
Destroys or inhibits growth of organisms on inanimate surfaces
What is decontamination
Removal of organisms
Properites of ideal disinfectant (7)
- Rapid activity against wide range of microbes
- Low/no toxicity
- No damage to surfaces or unwanted toxic residues
- Soluble in water
- Not affected too much by organic materials
- Safe and environmentally friendly
- Stability yet readily abilty to be broken down
Meaning of death for bacteria and factors which affect its measurement
Death means irreversible loss of ability to reproduce, factors include medium (solid/liquid), defined (minimal or complex), incubation period (time and temperature)
Define sterilization by moist heat
Moist heat (autoclave) is safer than dry heat (oven), in autoclaving the water disrupts the H-bonds between peptide groups, requires a lower T than dry heat and kills more efficiently. Uses steam to sterilise
Define sterilzation by dry heat
Requires a higher T than moist heat. Sterilzation is by an oxidative process and not recommended apart from materials that can’t be autoclaved. (powders)
Describe the 4 parameters of autoclaving
- Steam - must displace all air and requires time to heat up before timing of autoclaving commences
- Pressure - requires high pressure
- Temperature - 121 degrees celcius
- Time - 15 minutes
Define sterilisation by plasma
Plasma consists of H2O2 whose molecules have been excited by additional energy (charged nuclei, free radicals and free electrons.
Plasma can’t be used with molecules that absorb, decompose or react with H2O2.
Define ionising radiation
X-rays cause substances to ionise (free radicals) which inactivate many molecules (DNA), however it takes hours, penetrates glass and other materials and suitable for large scale use only.
Define chemical sterilisation by ethylene oxide or peracetic oxide
Ethylene oxide inactivates microbes by alkylation of proteins, DNA or RNA. However, it is toxic, doesnt inactivate prions, is a gas at RT and is flammable (mixed with CO2)
Define disinfection through pasteurisation
Pasteurisation is disinfection by heat (milk, wine). Decreases count by 97% but doesnt sterilise. Effective because milk pathogens don’t form spores. Pasteurisation is safe, reliable, cheap and no microbial resistance
Define disinfection through filtration (membrane or depth)
Filtration is used for heat sensitive liquids, prevents particles entering with liquid
Define disinfection through UV irradiation
UV light is non-ionising which alters electron orbits within atoms. Used to disinfect water supplies. Kills cells by forming pyrimidine dimers in bacterial DNA. However bacteria have enzymes which can repair UV damage. UV light has low penetrating power and organic matter can protect bacteria
Define disinfection by alchohol
Alcohol (usually ethanol) used to wipe down benches, kills in 30s, has no activity against spores and is flammable
Define disinfection by halogens
Halogens (bleach) used to clean blood spills, fast acting, non-flammable but inactivated by organic matter and unstable and corrosive.
Define disinfection by peroxygen compounds
Peroxygen compounds (virkon, peracetic acid and H2O2)
Define refrigeration and freezing for control of bacteria
Refrigeration is used to extend shelf life of substances and some bacteria can replicate in refrigeration
Freezing is used to preserve substances and bacteria, repeated freeze/thaw cycles reduces bacteria count. Glycerol is used to protect bacteria during freezing
Define hand-washing for control of bacteria
Hand-washing can terminate outbreaks of bacteria out of lab, reduces overall infection rates and plain soap used.
What are the 6 factors that affect efficacy of disinfectants
- Concentration of disinfectant - higher conc more sterile
- Organic matter - can block disinfectant
- Temperature - Activity increases with increased T
- pH - Anionic compounds more active at low pH, cationic compounds more active at low pH
- Drying - May encase bacteria in crystals and protect them
- Organism - Spores more R than vegetative cells, prions most difficult to inactivate
What are the two sterility check procedures
Monitor product status by microbiological assessment of sterilized item or material itself
Monitor sterilization process by mechanical, chemical and biological means
Define product testing
Product testing - A negative culture result only indicates that no organisms were detected
Define process monitoring
Process monitoring - either physical monitoring of process (thermometers, pressure gauges and gas analysis devices) or chemical which uses indicators to monitor conditions in dry heat, steam, ethlyene oxidiation and ionizing radiation.
