Topic 6 -Control of Microbial Growth

Question 1

What is sterilisation?

Answer 1

killing or removing all microorganisms

Question 2

What is commercial sterilisation?

Answer 2

killing c.botulinum endospores

Question 3

What is disinfection?

Answer 3

removing pathogens

Question 4

What is antisepsis?

Answer 4

removing pathogens from living tissue

Question 5

What is degerming?

Answer 5

removing microbes in a limited area

Question 6

What is sanitisation?

Answer 6

lowering microbial counts e.g. on utensils

Question 7

What is biocide/germicide?

Answer 7

kills microbes

Question 8

what is bacteriostasis?

Answer 8

inhibiting, not killing, microbes

Question 9

What is sepsis?

Answer 9

refers to microbial contamination

Question 10

what is asepsis?

Answer 10

the absence of significant contamination

Question 11

Name the death rate pattern of microbes, factors that effect effectiveness of treatment and physical control mechanisms

Answer 11

DRP -exponential decay (10 fold)
factors=> number of microbes, environment, time of exposure, microbial characteristics
phys. control=>filtration, desiccation (absence of water), osmotic pressure, radiation, heat

Question 12

What are the 3 ways microbial control agents work?

Answer 12

1. alterate membrane permeability
2. damage proteins
3. damage nucleic acids

Question 13

What is a thermal death point (TDP)? What is decimal reduction time (DRT)?

Answer 13

TDP-lowest temp. at which all cells in a culture are killed in 10mins
DRT-time (in mins) to kill 90% of a population at a given temp.

Question 14

Describe autoclaving

Answer 14

moist heat (steam) sterilisation under pressure. Temp acting on items is raised by increasing the pressure around the item
Kills all except prions

Question 15

How does dry heat sterilisation work? list 4 kinds

Answer 15

kills by oxidation
dry heat
flaming
incineration
hot-air-sterilisation

Question 16

What is the purpose of pasteurisation?

Answer 16

kills pathogens and reduces spoilage organisms. 63C for 30mins

Question 17

Describe how low temps suppress microbial growth

Answer 17

refrigeration: slows metabolic activity, bacteriostatic
freezing: ice crystals disrupt cells
freeze drying: decrease water availability

Question 18

identify appropriate use for surfactants

Answer 18

soap-degerming
acid-anionic detergents -sanitising
quarternary ammonium (cationic detergents) -bactericidal, denature proteins, disrupt plasma membrane

Question 19

Mode of action of halogens?

Answer 19

particularly iodine & chlorine

impairs protein synthesis and alters cell membranes

Question 20

mode of action of alcohols?

Answer 20

dissolves lipids, protein denaturation, disrupt membranes

Question 21

mode of action of heavy metals?

Answer 21

silver, mercury, copper

biocidal or antiseptic

Question 22

mode of action of peroxygens?

Answer 22

hydrogen peroxide, peracetic acid

oxidising agent

Question 23

Mode of action of super critical fluids?

Answer 23

carbon dioxide

inactivating using temperature

Question 24

mode of action of phenol/phenolics?

Answer 24

dsirupt plasma membranes

Question 25

mode of action of biguanides?

Answer 25

blocks lipid synthesis/disrupts plasma membrane

Question 26

antibiotics can affect?

Answer 26

cell wall, membrane, nucleic acid, essential metabolites

Question 27

What did Ehrlich contribute to antibiotics?

Answer 27

magic bullet idea -kill an invading pathogen but leave host alive
different organisms have different kinds of cells

Question 28

what did Fleming contribute to antibiotics?

Answer 28

magic bullet ‘penicillin’.