6.3.4 Bacteria Sterilisation

Question 1

What is sterilisation?

Answer 1

The process of making something free from bacteria or other living microorganisms

includes removal of spores

Question 2

List the microorganisms from most susceptible to least susceptible to disinfection methods

Answer 2

Vegetative bacteria > Fungi > Viruses > Mycobacteria > Non-enveloped viruses > Endospores

Question 3

In what temperature for how long should you keep vegetative bacteria to kill them?

Answer 3

60-70ºC for 5 min

Question 4

what’s the mechanism of killing vegetative bacteria?

Answer 4

denaturation of proteins, disruption of lipid membrane

Question 5

Why do we sterilise things?

Answer 5

Medicine and surgery

Microbiology

Food preparation

Question 6

What are the types of methods of sterilisation?

Answer 6

Physical: heat, radiation, filtration

Chemical

Question 7

What is an autoclave? How does it work?

Answer 7

moist heat (steam)

15 min / 121ºC or more

capable of destroying bacterial endospores

Question 8

How do we test the autoclave worked?

Answer 8

autoclave tape - white stripes go black when exposed to steam

Browne’s tubes - glass tubes containing red heat-sensitive dye, changes colour to green after a defined period of time at a certain temperature

spore strips - contain non-pathogenic spores, transferred aseptically to culture medium to germinate (if nothing - was properly sterilised, if sth grows - sterilisation faulty)

Question 9

What factors affect autoclaving?

Answer 9

steam penetration (moist heat required)

time to reach temperature (large volumes of liquid)

Question 10

Describe the dry heat physical sterilisation

Answer 10

hot air oven

45 min / 160ºC

glass, metal instruments, containers

Bunsen flame

microbiological loops

Question 11

What is tyndallisation?

Answer 11

heat to boiling point and hold 15 min, 3 days in succession

rest in between in a moist, warm environment to allow any surviving spores to germinate and then be killed

day 1. - vegetative organisms killed, spores activated

day 2. - germinated spores killed

day 3. - just to be sure

not reliable - some spores may survive

for things that cannot withstand pressurised heating, e.g. plant seeds

Question 12

What is pasteurisation?

Answer 12

slow: 63-66ºC x 30 min

rapid: 73ºC x 15 sec

kills M. bovis and B. abortus (and many others)

endospores not killed

disinfection / decontamination, not true sterilisation

Question 13

What are the methods of physical sterilisation using radiation?

Answer 13

UV light:
-poor penetration
-small scale
-‘clean’ surfaces

Gamma radiation:
-good penetration
-industrial scale
-source: 60C

Question 14

Describe filtration as a method of physical decontamination

Answer 14

membrane filter

not sterilising

pore size determines what passes through

used for e.g. drugs for injection

Question 15

What can be used for chemical sterilisation?

Answer 15

10% formalin

200ppm hypochlorite

10% ethylene oxide gas

Question 16

What is disinfection?

Answer 16

removal of most infective organisms, endospores and some viruses may survive

Question 17

How do disinfectants work? (mechanisms)

Answer 17

Target different part of the cells (e.g. cell envelope, cytoplasmic membrane, etc.)