Control Of microbial growth Flashcards
Define Themal death point
The lowest temperatre required to kill all organisms
Define thermal death time
The amount of time required to kill all organisms at a given temperatre
What are the 2 types of autoclaving
Gravity displacement or pre-vaccum
What is pasturisation
Killing of pathogens and reducing the spoilage oforganisms
What are the 3 types of pasturisation
HTST, UHTS
What are the conditions of HTST pasturisation
What are the conditions of UHT pasturisation
How does ionising radiation sterlise surgical equipment
By breaking double stranded dna (most commonly used is gamma or x-rays
What is sonification and how does to work to stertise
High frequency ultrasound waves, causes a rapid change in pressure. This is used to call cell lysis
What does oligodynamic mean
Active at small concentrations
What does desiccation mean
Reduction of water activity
What is ionising radiation used to sterilise
Heat sensitive and packaged material
What is non ionising radiation good for sterilising
Surfaces
What is the risk of using heavy metals as disinfectants
Their toxicity and the environmental risks
Where is chlorine typically used as a disinfectant
In water bodies such as swimming baths
What are the positives of using phenolics
They’re stable and long lasting
Where are HEPA filters typically used
In hospital ventilation systems it in labs
What are the positives and negatives of using alkylating agents to sterilise materials
They can effectively sterilise at low temperatures, but they’re carcinogenic
What factors can effect the effectiveness of disinfectants
What is disk diffusion used to check
Used to test efficacy against a particular microbe
What is use dilution used to check
To test efficacy on a surface
Why is moist heat more effective
Because it’s better able to penetrate the plastic packaging of instruments and is more effective at penetrating cell membranes
What is the disk diffusion method
Application of chemicals to filter paper, then placing them on agar, when the bacteria grows zones of inhibition will grow
What does the zones of inhibition show about the chemical and the bacteria
The larger the zone the more effective the chemical is at killing the bacteria.
How is the zone of inhibition measured
By calculating the area by measuring the diameter
What is the use dilution test
Penicylinders are soaked and dried in bacteria, are treated with disinfectant. They’re then placed into a growth media for 48 hours to determine if any have survived
What are the strengths of the use dilution test
Is a high level test for disinfectants.
Is an approved method by the environmental protection agency
What are the weaknesses of use dilution tests
They’re subject to variability.
They’re far removed from the real life use of disinfectants
What is the method for the in use test
1ml of disinfectant is mixed with 9ml of sterile broth ( with disinfectant inhibitor).
Then place 10 drops onto each of the 2 agars. Incubating one at 37•c for 3 days and the other at room temp for 7 days
What do the results of an in use test show
If 5+ colonies are viewed then contamination has occurred
What is the phenol coefficient method
Tests the potency of a disinfectant compared with phenol.
A series dilution is made and then test bacteria are added and incubated at 37•c.
Samples are taken at 5 minute intervals
If the value if larger than 1 then it implies better activity than phenol
What are the disadvantages of the phenol coefficient method
It can lead to misleading results
What is the number of common methods used to test potency of a disinfectant
Four
What type of heat do auto claves use
Moist
What’s another term for dessication
Drying
What happened to the boiling point of water at higher altitudes
What two things are used in high concentration in dessication
Salt and sugar
Which heavy metal is historically known to treat syphilis
Mercury
Which heavy metal causes argyria
Silver
What types of compounds facilitate the slow release of chlorine
Chloromines
What type of dimmers are caused by non ionising radiation
Thymine
What’s the type of compound where iodine is complexed with an organic molecule
Iodofour
In an auto clave what is air replaced by
Stream
What is the term used to denote complete removal or killing
Sterilisation
Beta- propionolactone is quickly metabolised into
Lactic acid
