Sterilisation 🧽🌡❌ Flashcards
Definition of sterilisation
Process of complete destruction or elimination of all viable microorganisms in or on a substance being sterilised.
Factors microbial growth is affected by
Temperature, ph, availability of oxygen, water, presence if pressure difference, radiation
Effect of heat in microorganisms
Do not grow outside defined pressure range?
Optimum temp- where most cellular components function most efficiently
Varies depending on microbe
Ecoli- 37 degrees
Candida- 25 degrees
Majority associated with human body =37 degrees
What happens to microorganisms when temp is too high or too low?
Low temp- gelling transport processes are slow or halted and therefore growth cannot occur
Too high- proteins start to denature, cytoplasmic membrane collapses, followed by thermal lysis and cell death
What are the names of the values that express the resistance of microorganisms to a sterilising agent?
D value and z value
What are survivor curves plotting?
Log of the fraction of survivors against exposure time or radiation dose
What is the assurance of sterility based on?
Probability if an organism surging the sterilisation procedure
Factors affecting heat sterilisation
Inherent resistance exhibited by a genus, species, strain, physiological state of cells and environmental factors induced by exposure before heat treatment
Limitations of sterility testing
Destructive- destroys sample/product
Can be false result as failure to detect microbes can be due to unsuitable media or inappropriate culture media
Viruses not detected
What are the two types of media that have been recommended for growth for sterilisation testing?
Fluid thioglycollate medium
Soya bean casein digest medium
Talk about Fluid thioglycollate medium
Suitable for cultivation of anaerobic bacteria
Contains agar
Thioglycollate acts as an oxygen scavenger
Typically incubated for 14 days at 30-35 degrees
Talk about soya bean casein digest medium
Used for detection of of aerobic and facultatively anaerobic bacteria and fungi
Allows growth for many species
Incubated for at least 7days at 20-25degrees for fungi - 30-35 degrees for bacteria
What is the method of testing sterilisation
Direct inoculation into recommended culture media and filtration using hydrophobic membrane filters which retain contaminants yet allow passage of product. Membrane washed to remove residual traces of product before transfer of the membrane to growth media.
What is a positive control and give example
They provide reassurance that contaminant would grown in test environment
Example = staphylococcus aureus , E.coli
Liquids amplification and culture disadvantages
Time consuming
Only detects relatively abundant contamination
Technically demanding
Loss of product
