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Physiology of Microbes > Biocides and Disinfection L19 > Flashcards

Biocides and Disinfection L19 Flashcards

1
Q

what did Pasteurs ‘germ theory’ lead to

A

washing hands before surgery
heat sterilisation of surgical instruments
carbolic spray into atmosphere to try reduce bacteria in atmosphere

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2
Q

what is an antimicrobial agent

A

Chemicals agents used to Kill or Inhibit growth of microbes

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3
Q

what is sterile

A

absolute term

No living organisms present. Even if there is one cell is not sterile

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4
Q

what do disinfectants and antiseptics kill

A

only vegetative cells

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5
Q

what do sanitizers do

A

kill only 99.9% of vegetative cells: reduce the microbial load to a safe level=

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6
Q

what is a bacterostatic antimicrobial antibiotics for

A

designed to inhibit bacteria

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7
Q

what is mycostatic antimicrobial agents for

A

designed to inhibit moulds

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8
Q

what happens in mould inhibition

A

inhibiting germination of moulds from the spores, will not necessarily inactivate the spore, but prevent outgrowth

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9
Q

what is fungistatic antimicrobial agents for

A

designed to inhibit fungi

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10
Q

where are fungistatics

A

usually on plants

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11
Q

what are fungistatics used for

A

crop production

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12
Q

what is sporocidal chemicals

A

particular chemicals that are targeted at those endospores

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13
Q

which spore is most and least robust

A

Fungal spores are generally less robust

Bacterial spores have particular robust structure that needs particular chemicals –sporicidal

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14
Q

why is antimicrobial agent virucidal not viralstatic

A

nothing top be static about as viruses are inert until they’re in the host cell

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15
Q

what is autoclaving

A

Temperature of boiling water increased by heating under pressure

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16
Q

what is used in autoclaving

A 
Wet heat (steam) is more penetrative and causes denaturation of macromolecules in cell
Especially proteins
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17
Q

what are the standard conditions in autoclaving

A

15 lbs/in2 at 121°C for 15-20 min

15 pounds/square inch

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18
Q

what is autoclaving the same as

A

domestic pressure cooker

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19
Q

what method scan be used to assess biocide activity

A

simple disk-diffusion method

quantitative suspension tests

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20
Q

what is simple disk-diffusion method

A

Paper disk soaked in test chemical is placed on a lawn of the test organism
Plates are incubated to identify any zones of killing

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21
Q

what is efficacy proportional to in simple disk-diffusion method

A

Efficacy is proportional to the zone size

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22
Q

what is the simple disk-diffusion method show

A

Want to know how effect the chemical is on certain microbes

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23
Q

in simple disk-diffusion what does a big zone of inhibition mean

A

bigger then inhibition zone ring the lower concentration that will kill your organism – sensitive to lower concentrations

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24
Q

what happens in the simple disk-diffusion method

A

Concentration of whatever youre looking at on the disk but it will diffuse out into the agar as the agar is wet, so have a chemical gradient, with highest conc in centre of the disk getting lower as go out into the zone of inhibition

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25
Q

what happens in quantitative suspension tests

A

Another way is to quantify the killing
Take a set number of cells and mix it with test chemical, incubate (often for long periods of time) look at the log reduction by preparing the serial dilutions and plating them out then counting the survivors

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26
Q

what is the D value

A

time to destroy 90% of the starting population for a given concentration of biocide

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27
Q

what is a 1 log10 drop

A

100 –> 10

90% of cells killed

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28
Q

how can cells be killed in D value

A

heat

biocides

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29
Q

what must we think about when picking a disinfection etc

A

Need to think about the amount of microbes that are present on the surface at the start to see what will be effective
e.g. if have 10^6 cells not even a 99.99% kill will clean it

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30
Q

what is important in biocide use

A

Appropriate “in use” concentration must be used

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31
Q

how long must biocide be left to work

A

Sufficient contact time (leave the antibacterial there for long enough, so get enough log drops to ensure its done its job to reduce microbes to safe level) must be used to ensure to allow the predicted population of microbes to be killed

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32
Q

what do biocides need

A

Relies on intimate contact with cell wall and membrane, needs to come into contact with cell wall if it is a biocide

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33
Q

what do biocides do

A

Physical structures are damaged and can no longer carry out vital processes e.g. respiration

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34
Q

what happens when biocides are used at sub-lethal concentrations

A

damage may be repaired/tolerated

Reversible growth inhibition occurs = sub-lethal injury

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35
Q

why are biocides used at sub-lethal levels constantly

A

When get damage that is not killing the cells but cells are having to put in energy to repair or to cope with the system they are expending energy to do this, which will inhibit growth

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36
Q

how do viruses repair

A

either dead or alive, cannot repair self if a virus

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37
Q

what are major groups of biocides

A

phenols

carboxylic acid

38
Q

what do phenols do

A

damage to proteins affects membrane permeability & general cellular functions

39
Q

what is an example of a o-phenylphenol

A

lysol

soaps in hospitals

40
Q

what is the difference between phenol and o-phenylphenol

A

Phenol is toxic

O-phenylphenol is less toxic, not toxic to use

41
Q

what do alcohols do to proteins

A

proteins denaturant

42
Q

what do alcohols do to lipids

A

will dissolve lipids (effect membrane structure and function)

43
Q

what do alcohols aid in cleaning

A

detergent action (help to wipe things off surfaces)

44
Q

what can we use on our skin to sanitise

A

ethanol for skin sanitisation (not toxic for us)

rapid sanitising when moving between areas

45
Q

what can’t we use on our skin to sanitise

A

methanol for surface sanitisation (toxic)

46
Q

why is ethanol effective against viruses

A

denatures protein so is very good against viruses, as it cannot repair

47
Q

what are the halogen biocides

A

iodine

chlorine

48
Q

what are the biocides

A 
alcohol
halogens
phenols
quaternary compounds
metals
49
Q

what are the effects of halogens on cellular components

A

oxidation of cellular components

50
Q

what does iodine do

A

will specifically combine with tyrosine residues, often found in active sites of enzymes
inhibit a wide range of different enzyme activity

51
Q

what is iodine used for

A

used with surfactants as acidic iodophores

52
Q

what does the chlorine biocide do

A

Chlorine and water form Hypochlorous acid and hydrochloric acid
hypochlorous acid will break down to release nascent oxygen

53
Q

what does chlorine do to protein

A

inactivates proteins

54
Q

what is chlorine used for

A

used in water disinfection and rinse waters

55
Q

what is a quaternary compound

A

cationic detergents

56
Q

what do cationic detergents

A

wetting ability

57
Q

what do quaternary compounds do

A

denatures proteins

58
Q

what are quaternary compounds good at

A

inactivating a wide range of microbes as affects membrane integrity affected

59
Q

what are the characteristics of quaternary compounds

A

low toxicity

non-corrosive

60
Q

what is the difference between quaternary compounds and chlorine

A

quaternary compounds don’t corrode metal, unlike chlorine

61
Q

what is quaternary compounds used for

A

extensively used for equipment as not corrosive

62
Q

what is the downside of using quaternary compounds

A

Expensive not easily made, so only use when no other alternative

63
Q

what is the general structure of quaternary compounds

A

Nitrogen group in the middle with various R groups and is complexed with an ion

64
Q

what action do metal biocides have

A

oligodynamic action

65
Q

when are metal biocides active

A

very low concentrations

66
Q

what do metal biocides do

A

combines with -SH (sulfhydryl) groups of proteins & inactivates them – so inactivates a wide range of microbes, by poisoning a lot of different processes

67
Q

what is added to reservoirs to remove fungi and algae

A

CuSO4 copper sulphate added to reservoirs

68
Q

what is an example of algicide and fungicide

A

copper sulphate

69
Q

what is a mild fungicide

A

zinc

70
Q

what is used for athlete

A

zinc

71
Q

what is an example of nanotechnology silver-containing

A

materials being developed, plastic tubs for food containers, low levels of silver leach out of the plastic and go into the food, so has contact so it works against microbes

72
Q

what is used to purify water

A

silver

73
Q

what is a problem with killing fungi

A

fungi is that a lot of their biochemistry (enzymes, structure) are very similar to ours, need to find something that will not effect us
Zinc good as we don’t not absorb it very well

74
Q

what is a biocide that is an oxidising agent

A

H2O2 hydrogen peroxide forms highly reactive superoxide (O2-)

75
Q

what does hydrogen peroxide do

A

rapidly degrades to O2 and H2O

76
Q

what does oxidising agent biocide do

A

Disrupts disulphide bonds

77
Q

what effect does disrupting disulphide bonds

A

Disulphide bonds primarily in membrane and cell wall, targeting things on the outside of the cell, it wont penetrate as it is so short lived

78
Q

what can be used to to clean wounds

A

hydrogen peroxide kills obligate anaerobes

79
Q

what are some of the characteristics of biocides

A

Alkylating agents
Disrupts both proteins and damages DNA
Donates CH3 or similar groups to DNA
causes inactivation of protein and DNA

80
Q

what can be used to sterilise equipment in plastic packaging

A

Ethylene oxide can diffuse through the semipermeable layer and sterile the equipment inside the plastic packaging

81
Q

what dyes are there that can be used to treat skin/wound disinfectants

A

acridine orange

crystal violet

82
Q

why can’t acridine orange be used

A

inhibits DNA replication and causes mutations

83
Q

why can’t crystal violet be used

A

inhibits cell wall synthesis of Gram- positive bacteria, at high concentrations will cause mutations

84
Q

what is important to consider when choosing a disinfectant

A

1) surface to be cleaned (alive, inert, will it be in contact with food etc)
2) concentration of organic matter present
3) importance of toxic residues

85
Q

what is important to consider when making disinfectant

A

If have a lot of organic spoil on a surface e.g. food or meat residue the chemical will also combine with the proteins in that, which dilutes them out. When designing disinfection have to think about how much will you need as some will be absorbed by other organic material in the system

86
Q

if targeting a gram negative bacteria what disinfectant is best to use

A

one that attacks lipids, will be most effective as have a lipid layer on outside

87
Q

what biological factors will affect disinfectants

A

Capsules may offer some protection by preventing biocide getting to active site

88
Q

how does the capsule effect the disinfectant

A

Slime layer / capsules protect self against environments
The first thing the chemical comes to is the slime layer, protected as it will be inactivated before it gets to the target site in the cell

89
Q

how does a biofilm form

A
  1. Cells that are floating around in the liquid phase of the environment will attach to surface. Cells undergo a change of gene expression (adaptive process)
  2. Capsule production induced
  3. Biofilm starts to thicken
  4. Complex communities with water channels which will aid nutrient exchange
  5. Cells revert to planktonic phenotype & are shed from biofilm
90
Q

what type of process is biofilm formation

A

adaptive process

91
Q

what does biofilm formation require

A

gene expression

92
Q

what may biofilm formation indicate

A

Often see this as a response of microbes growing in difficult environments

Physiology of Microbes (21 decks)

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