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MICR221 > L4 Physical control methods > Flashcards

L4 Physical control methods Flashcards

1
Q

define thermal death point

A

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

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2
Q

how is a thermal death point tested for

A

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

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3
Q

define thermal death time

A

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

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4
Q

how is a thermal death time found

A

heat cultures at the same temperature for different times

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

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5
Q

define decimal reduction time

A

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

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6
Q

another name for decimal reduction time

A

D-value

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7
Q

what does a ten-fold reduction mean?

A

90% is killed

1 log difference

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8
Q

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

A

decimal reduction time/ D-value

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9
Q

three terms used to assess the efficacy of heat treatments

A

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

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10
Q

what are the two principles involved in killing microorganisms

A
  • 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
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11
Q

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

A

measured sample
its spread out
the colonies are counted and graphed

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12
Q

what is K in terms of a D-value

A

death rate constant

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13
Q

what can filtration be used for

A

sterilising liquid and air

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14
Q

what is the usual pore size for a filter

A

0.2um

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15
Q

what are the three types of filters

A

depth (HEPA)
membrane
nucleopore

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16
Q

what does HEPA stand for

A

high efficiency particulate air filter

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17
Q

what is the structure of depth filter

A

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

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18
Q

disadvantages to a depth filter

A

retains a lot of liquid

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19
Q

what are depth filters usually used for these days

A

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

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20
Q

advantages to depth filter

A

high dirt handling capacity

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21
Q

structure of a membrane filter

A

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

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22
Q

what is the most commonly used filter for sterilisation

A

membrane

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23
Q

how does a membrane filter work

A

traps on the surface

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24
Q

disadvantages to a membrane filter

A

low dirt handling capacity (easily blocked)

-so very contaminated solutions need to be pre-filtered

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25
Q

structure of a nucleopore filter

A

polycarbonate film

completely uniform pores

26
Q

disadvantages to a nucleopore filter

A

very slow flow rate

27
Q

what is a nucleopore filter used for

A

processing samples for scanning electron microscopy

28
Q

what are the two types of biological safety methods

A

lamina flow hood

Class II biological safety cabinet

29
Q

how does a lamina flow hood work

A

blows sterilised air over the work space

30
Q

what does a lamina flow hood protect and how

A

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

31
Q

what does a Class II biological safety cabinet protect and how

A

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

31
Q

what does a Class II biological safety cabinet protect and how

A

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

32
Q

what are some examples of solutions that can be filtered

A 
tissue culture media 
serum
antibiotic solution
gasses
filtered beer
33
Q

microbe of the day

A

mycoplasma

34
Q

facts about mycoplasma

A

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

35
Q

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

A

mycoplasma

36
Q

why does mycoplasma require a smaller pore hole

A

no cell wall so it can squeeze through

37
Q

what are the two types of radiation

A

ionising

non-ionising

38
Q

what are some examples of ionising radiation

A

X-Ray
gamma
cathode

39
Q

what are some example of non-ionising radiation

A

UV

40
Q

what does ionising radiation result in?

A

sterilisation

41
Q

what does non-ionising radiation result in?

A

disinfection

42
Q

how does non-ionising radiation work

A

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

43
Q

application of UV radiation

A

air and bench serilisation

44
Q

why cant UV be used to sterilise large volumes of liquid

A

cannot penetrate it to a significant depth

45
Q

how does UV light affect DNA

A

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

46
Q

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

A

nucleotide ecision repair
direct repair
recombinational repair
SOS repair

47
Q

what happens during nucleotide excision repair

A

The UvrABC endonuclease removes damaged nucleotides

the gap in the single strand is repaired by polymerase and ligase

48
Q

what happens during direct repair

A

photoreactivation

uses visible light and photolyase

49
Q

what does recombinational repair involve

A

Uses Rec A enzyme to correct damaged DNA

50
Q

what does SOS repair involve

A

transcriptional repressor protien

many genes

51
Q

which repair system is used as a last resort and why

A

SOS repair as it is very error prone

52
Q

when does cell death occur

A

when damage is greater than repair

53
Q

order from most to least UV sensitive types of bacteria

A

gram negative
gram positive
endospores

54
Q

why is ionising radiation more suitable for control

A

the shorter wave lengths carry more energy

55
Q

how does ionising radiation kill bacteria

A

indirectly by inducing reactive chemicals (free radicals)

it breaks individual molecules into ions hence ionising radiation

56
Q

what does gamma radiation do to water

A

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

57
Q

why is ionising radiation indirect

A

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

58
Q

applications of ionising radiation

A

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

59
Q

disadvantages to gamma radiation

A

expensive

dangerous (requires lead sheilds)

MICR221 (23 decks)

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