Lecture 3

Question 1

What is a pure culture ?

Answer 1

Contains only one kind of organisms

Question 2

Why is it important to work in a sterile way ? (2 reasons)

Answer 2

Avoid contamination of your samples AND for our and other people’s safety (protect from infections)

Question 3

What are the definitions of sterility and sterilization

Answer 3

sterility = state of being free from VIABLE microorganisms.
Sterilization = killing / removal of all viable microorganisms (probability of absence)

Question 4

What is SAL ? Standard value ?

Answer 4

SAL = sterility assurance level (prob of non sterility) -> 10^-6 is standard = one spore out of a million survives

Question 5

Are disinfection and sterilization the same ?

Answer 5

NO ! disinfection only kills actively growing microorganisms to a certain level, and doesn’t apply to endospores

Question 6

What is the bioburden ? What can it influence ?

Answer 6

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

Question 7

What are biological indicators used for ?

Answer 7

They are preparations of high resistance microorganisms -> test how efficient a sterilization technique is

Question 8

Three characteristics of biological indicators : D, Z, F

Answer 8

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)

Question 9

4 ways to kill microbes (only names, other cards describe them)

Answer 9

heat, radiation, chemicals, mechanical (filter -> remove from sample)

Question 10

wet heat and dry heat : describe

Answer 10

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

Question 11

Ionizing radiation : elements used, applied dose, pros and cons

Answer 11

• 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)

Question 12

UVs : optimal range, limitation ?

Answer 12

240 - 280 nm
Low penetrating power -> limited to treatment of water and surfaces (robots in hospitals, biosafety cabinets in labs)

Question 13

Infra-red : usage, similar to what ?, inactivation mechanism

Answer 13

Inactivate bacteria, spores, yeast, mold.
Similar to dry heat.
DNA damage in addition to thermal effect.

Question 14

A few examples of chemical disinfectants

Answer 14

alcohol, chlorine (bleach), peroxygen compounds, chlorine gas, ethylene oxyde (gas), hydrogen peroxyde (gas)

Question 15

Ethylene oxide : mode of action, pros, cons

Answer 15

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, …

Question 16

Hydrogen peroxyde : mode of action ?, in what form it’s used, disadvantage ?

Answer 16

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)

Question 17

Chloride dioxyde : mode of action, advantage

Answer 17

Disrupts cells metabolism by reacting with proteins in cell membrane. Also reacts with DNA and RNA.
True gas, so easier to handle than H2O2

Question 18

Sterile filtration : purpose, when ?, what are some things to consider

Answer 18

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, …

Question 19

What are the two main targets of medical antimicrobials against bacteria ?

Answer 19

1) cell wall synthesis
2) protein synthesis (different ribosomes than human)

Question 20

Main targets of medical antimicrobials agains fungi ?

Answer 20

Ergosterol synthesis (erogsterols are in fungi cell membrane).
Cell wall synthesis.

Question 21

3 main targets of medical antimicrobials against viruses ?

Answer 21

1) absorption, penetration and uncoating (release of genetic material)

2) transcription and replication

3) Assembly of new viruses (packaging)