Microbial Control Flashcards
What is the difference between sterilisation and sanitisation?
Sterilisation- the removal of all microbes including bacterial spores
Sanitisation- the destruction of various microorganisms to reduce viable numbers on clean surfaces to meet product quality and public health standards
What is the difference between a disinfectant and an antiseptic?
Disinfectant- substance that removes or destroys pathogens from inanimate areas
Antiseptic- disinfectant for animate areas
What is pasteurisation
A process developed by Louis Pasteur that reduces spoilage bacteria and increases the shelf life
What are the temperatures and times for LTLT and HTST relating to pasteurisation
Low temp - long time : 63 degrees for 30 mins
High temp - short time : 72 degrees for 15 sec
List 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 iodophors and detergent which is used as a skin disinfectant in pre-surgical operations. List the advantages and disadvantages of Betadine for this use?
Advantage - good residual effect, effective on a wide range of microbes, good for treatment on small wounds, surgical scrub, pre-operative skin disinfection
Disadvantage - skin discolouration, hypersensitivity, pseudomonas able to grow
What is the mechanism of action for Quaternary Ammonium Compounds (QUATs) against bacteria
They are surface active agents; they can disrupt the cell membrane of the target microorganism
Why are QUATs no longer used in some hospital settings
Skin/ respiratory irritation
Pseudomonas can grow in QUATs
How could the presence of organic matter interfere with the action of disinfectants
Forms precipitate - removes disinfectant from contact with bacteria
Reacts with the disinfectant to produce a non-bacterial agent
Coats bacteria - protects bacteria from the disinfectant
UV radiation damages proteins and nucleus acid if bacteria. What is the main disadvantage of UV radiation as a disinfectant
The radiation is not very penetrative, so for the organism to be killed must be directly exposed to the rays
What is the ‘decimal reduction time (D)’
The time in minutes for the survivors to be destroyed by one log cycle which represents 90% of the initial population
What is sterilisation
A process in which all microbes including endpapers are destroyed
Why are endoscopes difficult to kill
Most heat resistant and difficult to kill microbial structure
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 penetration
In what circumstances would you probably use a dry heat oven instead of autoclaving
Dry heat ovens are used to sterilise items that might be damaged by moist heat or might be susceptible to corrosion
Good for glassware, oils, powders - that you don’t want to get wet
What methods are used to ensure an autoclave is working
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 autoclave is not successful
Autoclave tape - stripes on a strip of tape are white before sterilisation, tape is placed inside the autoclave, if there are best lines on the tape then autoclave is successful, if they are faded out then it is unsuccessful, this brings an immediate result but does not indicate the time held
Name two chemicals used for ‘cold sterilisation’
Cold sterilisation works to denature proteins
Formaldehyde and ethylene oxide can be used for cold sterilisation
How does ionising radiation affect microbes and kill them
Has the energy to liberate an electron from an atom
State the filtration pore size needed to filter out a) bacteria, b) viruses l
Bacteria - 0.45 micrometer um
Viruses - 0.01 micrometer um
What is the difference between bacteriostatic and bactericidal agents
Bacteriostatic - inhibit growth of bacteria
Bactericidal - kill bacteria
List the 6 modes of actions for antibacterial agents
1 - inhibitors of cell wall synthesis
2 - membrane-active antimicrobial agents
3 - inhibitors of DNA replication
4 - inhibitors of RNA synthesis
5 - inhibitors of ribosome function - protein synthesis
6 - metabolic inhibitors
Describe the action of the B-lactam antibiotics
B-lactams inhibit the last stage of the cell wall production processes Eukaryotic cells (including humans) do not have a cell wall (only plasma membrane) and no peptidoglycan, the B-lactams work well in that they kill bacteria without damaging cells if the host.
- the ring must be intact for antibacterial activity, inactivated by beta lactamase enzymes of bacteria
- these agents bond 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 B-lactams are bactericidal)
- not effective against eating bacteria
B-lactams inhibit the last stage of the cell wall production processes
Not effective against resting bacteria
These agents bind to proteins at the cell wall/ cell membrane interface (PBPs) that are involved in the cross linking of peptidoglycan strands - results in cell lysis
How could incompletion of a prescribed course of antibiotics lead to bacterial resistance
Not completing a course of antibiotics (that woke) = 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
Natural compounds produced by microorganisms that kill or inhibit other microorganisms
Antibiotic creed
The guidelines doctors go by to determine how much of an antibiotic to prescribe to a patient
Why are B-lactam agents good for treating susceptible bacterial infections in humans
Eukaryote cells (including humans) do not have a cell wall (only a plasma membrane) and no peptidoglycan,the B-lactams work well in that they kill bacteria without damaging cells of the host
Why are many treatments for fungal infections often toxic to humans
Fungi are difficult to treat because they are eukaryotic and so have similar structures to human cells
Can kill human cells along with fungal cells
List two modes of action for antiviral drugs
- Prevention of uncoating of virus (e.g. Amantadine for influenza)
- inhibit viral replication (e.g. Aciclovit for Herpes)
