L4 Physical control methods

Question 1

define thermal death point

Answer 1

lowest temperature to kill all cells in a standard suspension of bacteria in a liquid culture within 10 minutes

Question 2

how is a thermal death point tested for

Answer 2

heating bacteria in solution to different temperatures for the same time
streak, incubate and check agar for growth compared to a control section

Question 3

define thermal death time

Answer 3

LENGTH OF TIME to KILL all of the cells in a standard suspension of bacteria in a liquid culture at a given temperature

Question 4

how is a thermal death time found

Answer 4

heat cultures at the same temperature for different times

streak, incubate and check agar plates for growth compared to a control (untreated)

Question 5

define decimal reduction time

Answer 5

LENGTH OF TIME taken to obtain a TEN-FOLD reduction in the number of bacter in a standard suspension of bacteria in liquid culture
-it is independent of the initial population

Question 6

another name for decimal reduction time

Answer 6

D-value

Question 7

what does a ten-fold reduction mean?

Answer 7

90% is killed

1 log difference

Question 8

what term is most commonly used to assess the efficacy of heat treatments

Answer 8

decimal reduction time/ D-value

Question 9

three terms used to assess the efficacy of heat treatments

Answer 9

thermal death point
thermal death time
D-value/ decimal reduction time

Question 10

what are the two principles involved in killing microorganisms

Answer 10

• death from heating is an exponential function and thus occurs more rapidly as the temperature is raised
• to sterilise or reduce a population it will take longer at lower temperatures than at higher temperatures

Question 11

what are the important things to know about a D-value

Answer 11

measured sample
its spread out
the colonies are counted and graphed

Question 12

what is K in terms of a D-value

Answer 12

death rate constant

Question 13

what can filtration be used for

Answer 13

sterilising liquid and air

Question 14

what is the usual pore size for a filter

Answer 14

0.2um

Question 15

what are the three types of filters

Answer 15

depth (HEPA)
membrane
nucleopore

Question 16

what does HEPA stand for

Answer 16

high efficiency particulate air filter

Question 17

what is the structure of depth filter

Answer 17

random array of overlapping fibres
asbestos, glass or paper
5-7mm thick

Question 18

disadvantages to a depth filter

Answer 18

retains a lot of liquid

Question 19

what are depth filters usually used for these days

Answer 19

pre-filter to remove large particles or a large number of particles to reduce clogging in final filtration
biological safety cabinets

Question 20

advantages to depth filter

Answer 20

high dirt handling capacity

Question 21

structure of a membrane filter

Answer 21

regular pore size (uniform/known diameter)
made from cellulose acetate or cellulose nitrate
thin as paper

Question 22

what is the most commonly used filter for sterilisation

Answer 22

membrane

Question 23

how does a membrane filter work

Answer 23

traps on the surface

Question 24

disadvantages to a membrane filter

Answer 24

low dirt handling capacity (easily blocked)

-so very contaminated solutions need to be pre-filtered

Question 25

structure of a nucleopore filter

Answer 25

polycarbonate film | completely uniform pores

Question 26

disadvantages to a nucleopore filter

Answer 26

very slow flow rate

Question 27

what is a nucleopore filter used for

Answer 27

processing samples for scanning electron microscopy

Question 28

what are the two types of biological safety methods

Answer 28

lamina flow hood | Class II biological safety cabinet

Question 29

how does a lamina flow hood work

Answer 29

blows sterilised air over the work space

Question 30

what does a lamina flow hood protect and how

Answer 30

the speciman but not the user as blows the contaminated air out without sterilisation

Question 31

what does a Class II biological safety cabinet protect and how

Answer 31

user and speciman It has a glass screen protecting the user as well and a vent that absorbs air leaving the top and front It blows sterilised air into the cabinet

Question 31

what does a Class II biological safety cabinet protect and how

Answer 31

user and speciman It has a glass screen protecting the user as well and a vent that absorbs air leaving the top and front It blows sterilised air into the cabinet

Question 32

what are some examples of solutions that can be filtered

Answer 32

``` tissue culture media serum antibiotic solution gasses filtered beer ```

Question 33

microbe of the day

Answer 33

mycoplasma

Question 34

facts about mycoplasma

Answer 34

lack a cell wall resisitant to anti-biotic like beta-lactams due to lack of cell wall smallest bacteria yet discovered some are pathogens

Question 35

what is the bacteria that requires a 0.1um pore when filtering

Answer 35

mycoplasma

Question 36

why does mycoplasma require a smaller pore hole

Answer 36

no cell wall so it can squeeze through

Question 37

what are the two types of radiation

Answer 37

ionising | non-ionising

Question 38

what are some examples of ionising radiation

Answer 38

X-Ray gamma cathode

Question 39

what are some example of non-ionising radiation

Answer 39

UV

Question 40

what does ionising radiation result in?

Answer 40

sterilisation

Question 41

what does non-ionising radiation result in?

Answer 41

disinfection

Question 42

how does non-ionising radiation work

Answer 42

UV light (wavelength 260nm) damages DNA by forming pyrimidine dimers or direct protein damage

Question 43

application of UV radiation

Answer 43

air and bench serilisation

Question 44

why cant UV be used to sterilise large volumes of liquid

Answer 44

cannot penetrate it to a significant depth

Question 45

how does UV light affect DNA

Answer 45

covalent chemical bonds form between adjacent thymine molecules forming a thymine diamer

Question 46

what are the 4 types of repair systems bacteria use to remove the thymine diamers

Answer 46

nucleotide ecision repair direct repair recombinational repair SOS repair

Question 47

what happens during nucleotide excision repair

Answer 47

The UvrABC endonuclease removes damaged nucleotides | the gap in the single strand is repaired by polymerase and ligase

Question 48

what happens during direct repair

Answer 48

photoreactivation | uses visible light and photolyase

Question 49

what does recombinational repair involve

Answer 49

Uses Rec A enzyme to correct damaged DNA

Question 50

what does SOS repair involve

Answer 50

transcriptional repressor protien | many genes

Question 51

which repair system is used as a last resort and why

Answer 51

SOS repair as it is very error prone

Question 52

when does cell death occur

Answer 52

when damage is greater than repair

Question 53

order from most to least UV sensitive types of bacteria

Answer 53

gram negative gram positive endospores

Question 54

why is ionising radiation more suitable for control

Answer 54

the shorter wave lengths carry more energy

Question 55

how does ionising radiation kill bacteria

Answer 55

indirectly by inducing reactive chemicals (free radicals) | it breaks individual molecules into ions hence ionising radiation

Question 56

what does gamma radiation do to water

Answer 56

water + gamma = positive water + electron electron + water = negative water positive water = strong reducing agent H + strong oxidising agent OH negative water = "

Question 57

why is ionising radiation indirect

Answer 57

the radiaiton causes molecule to split into free radicals which then go on to react and damage the bacteria

Question 58

applications of ionising radiation

Answer 58

penetrating radiation so it can sterilise products after packages (food preservation) sterilise lab products: petri dishes sewage treatment

Question 59

disadvantages to gamma radiation

Answer 59

expensive | dangerous (requires lead sheilds)