Microbial Control
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What is the difference between sterilisation and sanitisation?
Sterilisation: the destruction of all microbes Sanitisation: the destruction of many microorganisms to reduce viable numbers
What is the difference between a disinfectant and an antiseptic?
Disinfectant: destroys microbes on inanimate objects Antiseptic: a disinfectant for animate areas
What is pasteurisation?
A process developed by Louis Pastuer that reduces spoilage bacteria and increases the shelf life of food
What are the temperatures and times for LTLT and HTST relating to pasteurisation?
LTLT: 63 degress, 30 min HTST: 72 degrees, 15 sec
List the 3 modes of action for disinfectants?
• Protein coagulation/denaturation • Disruption of cell membrane • Chemical antagonism (inactivation of enzymes)
What is the optimal percentage of alcohol for disinfection?
70%
Betadine is a combination of iodophor and detergent which is used as a skin disinfectant in presurgical operations. List the advantages and disadvantages of Betadine for this use.
Advantages: - good treatment for small wounds and infections - effective on a wide range of microbes - can be a pre-operation skin disinfectant Disadvantages: - can cause discolouration of skin - can lead to hypersensitivity of skin - psuedonomas are able to grow from it
What is the mechanism of action for Quaternary Ammonium Compounds (QUATs) against bacteria?
• They are surface active agents
Why are QUATS no longer used in some hospital settings?
• Can be inactivated by soaps, low level disinfectants
What is the “decimal reduction time (D)”?
The ‘decimal reduction time’ (D) is the time (minutes) for the survivors to be destroyed by one log cycle which represents 90% of the initial population
What is Sterilisation?
The destruction of all microbes
Why are endospores difficult to kill?
• They are the most heat resistant and difficult to kill microbial structure • The thick spore coat protects from radiation and chemicals
Why is moist heat better than dry heat?
• Moist heat (autoclave) is more effective than dry heat (hot air oven) • Moisture is a better conductor of heat and has better heat penetration
In what circumstance would you probably use a dry heat oven in stead of autoclaving?
• When sterilising glassware, oils and powders (it doesn’t make sharps blunt)
What methods are used to ensure an autoclave is working?
• Autoclave prinouts/monitoring • Spore strips: endospores put on paper strip inside envelope, placed inside autoclave, transferred to broth and incubated at 55 degrees for 5 days, if there is growth then the autoclave is successful, if not, then it is not • Autoclave tape: Stripes on a strip of tape are white before sterilisation, tape is placed inside the autoclave, if there are neat lines on the tape then autoclave is successful, if they are faded out then it is unsuccessful, the brings an immediate result but does not indicate the time held
Name two chemicals used for “cold sterilisation”. How does ionizing radiation affect microbes and kill them?
• Cold sterilisation works to denature proteins - Formaldehyde and ethylene oxide can be used for cold sterilisation
State the filtration pore size needed to filter out a) bacteria, b) viruses
• Bacteria: 0.45 micrometres or less - Virus: 0.01 mircrometre or less
What is the difference between Bacteriostatic and Bactericidal agents?
• Bacteriostatic: inhibit growth of bacteria - Bactericidal: kill bacteria
List the 6 modes of action for anti-bacterial agents (i.e. 6 target sites).
• Inhibitors of cell wall synthesis • Membrane-active antimicrobial agents • Inhibitors of DNA replication • Inhibitors of RNA synthesis • Inhibitors of ribosome function - protein synthesis • Metabolic inhibitors
Describe the action of the β-lactam antibiotics.
• 𝛃- lactams inhibit the last stage of the cell wall production process • Not effective against resting bacteria • These agents binds to proteins at the cell wall/cell membrane interface (PBPs) that are involved in the cross linking of the peptidoglycan strands – results in cell lysis (all are bactericidal)
How could incompletion of a prescribed course of antibiotics lead to bacterial resistance?
• Not completing a course of antibiotics (that work) = selecting resistant mutants
Why are antibiotics of no use against the common cold?
• The common cold is a virus, antibiotics work on bacterial infections
Define “antibiotic”. Define the ‘Antibiotic Creed’.
• Antibiotic: natural compounds produced by microorganisms that kill or inhibit other microorganisms • Antibiotic Creed: the guidelines doctors go by in order to determine how much of an antibiotic to prescribe to a patient
Why are the β-lactam agents good for treating susceptible bacterial infections in humans?
• Because eukaryote cells (including humans) do not have a cell wall (only a plasma membrane) and no peptidoglycan, the β-lactams work well in that they kill bacteria without damaging cells of the host