Lecture 3 Flashcards
What is a pure culture ?
Contains only one kind of organisms
Why is it important to work in a sterile way ? (2 reasons)
Avoid contamination of your samples AND for our and other people’s safety (protect from infections)
What are the definitions of sterility and sterilization
sterility = state of being free from VIABLE microorganisms.
Sterilization = killing / removal of all viable microorganisms (probability of absence)
What is SAL ? Standard value ?
SAL = sterility assurance level (prob of non sterility) -> 10^-6 is standard = one spore out of a million survives
Are disinfection and sterilization the same ?
NO ! disinfection only kills actively growing microorganisms to a certain level, and doesn’t apply to endospores
What is the bioburden ? What can it influence ?
it is used to describe the microbial numbers on a surface, inside a device, in a portion of air, …
Can influence the choice of sterilization technique
What are biological indicators used for ?
They are preparations of high resistance microorganisms -> test how efficient a sterilization technique is
Three characteristics of biological indicators : D, Z, F
D = level of resistance : time taken to reduce the population of a microorganism by 1 log (100% to 10%)
Z : number of °C (or another parameter like concentration) required to change D by one factor of 10 (one log)
F : duration in minutes required to achieve a given reduction ratio at constant T (compare different processes)
4 ways to kill microbes (only names, other cards describe them)
heat, radiation, chemicals, mechanical (filter -> remove from sample)
wet heat and dry heat : describe
Wet = autoclave : steam under pressure (above 100°C). 10-15 min at 121°C for endospores.
Dry = oven : higher T and a lot longer cycles
Ionizing radiation : elements used, applied dose, pros and cons
- 60Co, 137Cs
- dose in range 25-50 kGy
- pros : high penetrating power (products still in packaging), rapid and low cost, low T, flexible
- con : not compatible with all materials, can break down the packaging (plastics)
UVs : optimal range, limitation ?
240 - 280 nm
Low penetrating power -> limited to treatment of water and surfaces (robots in hospitals, biosafety cabinets in labs)
Infra-red : usage, similar to what ?, inactivation mechanism
Inactivate bacteria, spores, yeast, mold.
Similar to dry heat.
DNA damage in addition to thermal effect.
A few examples of chemical disinfectants
alcohol, chlorine (bleach), peroxygen compounds, chlorine gas, ethylene oxyde (gas), hydrogen peroxyde (gas)
Ethylene oxide : mode of action, pros, cons
Reacts with amino acids and proteins -> makes them useless for the cell.
Pro : compatible with many materials, good penetration, easy to tune (T, pressure, …).
Cons : flammable, can explode, …
Hydrogen peroxyde : mode of action ?, in what form it’s used, disadvantage ?
Mode of action still poorly understood. It’s used in a vapor form. Disadvantage is that the vapor droplets don’t necessarly go on the whole surface (compared to a gas)
Chloride dioxyde : mode of action, advantage
Disrupts cells metabolism by reacting with proteins in cell membrane. Also reacts with DNA and RNA.
True gas, so easier to handle than H2O2
Sterile filtration : purpose, when ?, what are some things to consider
Use filters to remove microorganisms. Used when the other three treatments can’t be used (product too sensitive).
Consider : type of particle, filter material, filter thickness and porosity, type of fluid, …
What are the two main targets of medical antimicrobials against bacteria ?
1) cell wall synthesis
2) protein synthesis (different ribosomes than human)
Main targets of medical antimicrobials agains fungi ?
Ergosterol synthesis (erogsterols are in fungi cell membrane).
Cell wall synthesis.
3 main targets of medical antimicrobials against viruses ?
1) absorption, penetration and uncoating (release of genetic material)
2) transcription and replication
3) Assembly of new viruses (packaging)
