Controlling Microbial Growth: Sterilisation, Disinfection and Antisepsis Flashcards
What is the difference between sterilisation, disinfection, and antisepsis?
Sterilisation kills everything Disinfection removes majority of organisms but not spores Antisepsis is the external application of chemical agent to live tissue to kill or inhibit the growth of organisms (lowers risk of infection)
What kind of death do microbes exhibit?
Exponential or logarithmic.
What factors does extent of survival of microbes depend on?
Initial population size Duration of exposure Antimicrobial concentration Presence of organic matter (protects microbes and inactivates chemical agents)
What structures provide protection for microbes from disinfectants?
Endospores Cell envelope Efflux pumps
What do endospores do for protection of microbes?
Bacterial endospores are resistant to heat, radiation, and chemicals
What do cell envelopes do?
Their structure protects them from certain chemical agents. (mycobacterium tuberculosis uses this mechanism)
What do efflux pumps do?
They pump disinfectants and antiseptics out of the cell.
Order the following from most resistant to least resistant to decontamination: Bacterial spores, prions, fungi, vegetative bacteria, lipid or medium sized viruses, mycobacteria, cryptosporidium, non-liipid or small viruses
Prions Bacterial spores Cryptosporidium Mycobacteria Nonlipid or small viruses Fungi Vegetative bacteria Lipid or medium-sized viruses
Why was pasteurization of milk developed?
In order to prevent milk from transmitting tuberculosis or typhoid
What vaccines did pasteur develop?
Anthrax and rabies
When is sterilization used?
Surgical instruments Disposal of lab cultures. Sterilization has 4 basic stages
What are the 4 basic stages of sterilisation?
Inspection/scrubbing/rinsing (removes organic matter that may protect microbes and reduce efficiency of sterilisation) Packaging (instruments individually wrapped in sterilisation paper or sterilisation bag) Sterilization Storage in proper conditions
How is sterilization conducted?
Moist heat (= In autoclave) Dry heat (= In hot air oven) Dry heat and toxic gases (= In chemiclave) Radiation (UV or ionizing radiation)
How does autoclave inactivate microorganisms?
Using a combination of temperature and pressure. (disrupts cell membranes, denatures proteins, degrades nucleic acids)
What controls must be used for autoclave?
Routine monitoring (view temp and pressure gauges or readout. Chemical indicators (colour change in response to heat/pressure) Biological indicators (bacterial endospores that grow if not killed by autoclave process)
How does dry heat sterilisation inactivate microbes?
Disrupts membranes Denatures/degrades biological molecules. (proteins + nucleic acids)
What is dry heat sterilisation used for?
Items that would be damaged by moist heat or impenetrable to moist heat.
What are the disadvantages to dry heat sterilisation?
Dry air conducts heat poorly Long cycle time (2 hours at 160degrees)
What does a chemiclave do?
Uses a mixture of toxic gases (formaldehyde, alcohols, acetone, ketones) Dry process with low humidity (7 - 8%) Uses high temp/pressure combination (127 - 132 degrees 138 - 176 kPa)
How do items come out of an autoclave?
Wet typically
What is the downside to using chemiclave or gas sterilisation?
Toxic fumes are a potential problem.
What methods are used for sterilising heat sensitive items?
Gas sterilisation UV radiation Ionising radiation Membrane filtration
What is gas sterilisation?
Chemical vapour combined with low temperature (similar to chemiclave but at lower temperature (38 - 54 degrees), chemicals kill microbes by chemical modification of proteins, used to sterilise plasticware, syringes, sutures, and catheters.
How does UV sterilisation work?
260 nm wavelength radiation kills by damaging DNA and inhibiting DNA replication. (generates covalent links between adjacent thymine bases in DNA)
What are the limitations of UV sterilisation?
Limited use because it does not penetrate glass, water or other substances. It is most commonly used to sterilise internal cavity of laminar flow cabinets.
What is gamma radiation used for?
Highly sensitive chemicals like antibiotics, sutures, plastics, hormones, and other disposables.
How does gamma radiation kill?
By inducing chemical changes to biological molecules. Polymerises some molecules, breaks H-bonds, oxidises double bonds, destroys ring structures.
How is gamma radiation emitted?
During cobalt 60 radioisotope decay.
How does membrane filtration work?
Solution is passed through a synthetic membrane with tiny pores (0.2micrometer diameter) and does not exclude mycoplasma species, and viruses.
What is membrane filtration used to sterilize?
Heat-sensitive pharmaceuticals Opthalmic solutions Laboratory culture media
What is disinfection?
Process that kills or removes the majority of organisms but not spores. Use of chemical control agents for large fixed items or sites. Items that are too large to put into an autoclave are disinfected.
Why is disinfection so necessary?
Bacteria can survive for years on surfaces even without endospores.
Who first developed antiseptic surgery?
Joesph Lister
How are disinfectants classified?
Low-level: Active against most bacteria and fungi but not active against M.tuberculosis or endospores.
Intermediate level: Active against gram positive, gram negative, M.tuberculosis, and most viruses and fungi, but not active against endospores.
High-level: Active against gram positive, gram negative, endospores, M.tuberculosis, fungi, viruses, also known as chemical sterilants.
What are low level disinfectants used for?
Skin antisepsis
Examples of low-level disinfectants:
Chlorhexidine (disrupts cell membranes, leads to permeability, and death) [used in handwash]
Quaternary ammonium compounds (cationic detergents, disrupt cell membranes, used to disinfect surfaces, they denature proteins)
What are the disadvantages to using quaternary ammonium compounds?
They are inactivated by hard water and soap.
What are 3 intermediate-level disinfectants?
Alcohol
Halogen compounds
Phenolics
Does alcohol become more effective at higher concentrations?
No
What are the disadvantages to using alcohols?
Evaporates quickly and is inactivated by organic matter
What are alcohols used for?
Skin antisepsis and hand hygiene
Acts by perturbing cell membranes.
What are halogen compounds used for?
Skin antisepsis and hypochlorite is used to disinfect surfaces
How do halogen compounds work?
Act by oxidising a wide array of biological molecules.
What are the disadvantages to using halogen compound disinfectants?
They can corrode metal and are inactivated by organic matter
Why is the use of 70% alcohol better than 100%?
The dehydration of the cell membrane makes it happen so quickly that it seals it while the inside of the cell is still alive.
What are phenolics?
Chemical derivatives of phenol that are used widely for decontamination of surfaces. They kill by disruption of cell membranes and denaturing proteins.
What are the advantages and disadvantages of using phenolics?
Advantages:
Remain active for long periods after application
Not readily inactivated by organic matter
Disadvantages:
Highly irritating to skin
What do aldehydes do?
They kill by chemical modification/cross-linking of proteins. Immersion in glutaraldehyde for long time periods may achieve sterilisation.
What are the disadvantages to using aldehydes?
They are very toxic and they irritate the skin.
Vapours are irritating to eyes and respiratory tract.
Rarely used as a disinfectant and use is banned in some countries due to long term health effects.
What is the purpose of antisepsis?
Reduces risk of infection in patient and reduces transmission of pathogen by healthcare workers.
What is antisepsis?
Use of disinfectants to reduce number of microorganisms on the skin.
