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Physiology of Microbes > Toxicity and Ames L20 > Flashcards

Toxicity and Ames L20 Flashcards

1
Q

what do different chemicals do

A

affect microbes in different ways and a critical threshold is required to achieve killing

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2
Q

what happens when microbes are exposed to sub-lethal concentrations

A

microbes can survive

cells can repair damage (NOT VIRUSES)

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3
Q

what does repeated exposure to sub-lethal concentrations of chemicals do

A

chemicals, including antibiotics can lead to resistance due to mutations

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4
Q

what can occur in large populations to do with mutations

A

even rare mutations will occur

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5
Q

what is toxicity

A

relative phenomenon

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6
Q

what does toxicity depend on

A

1) innate toxicity of a substance
2) dose administered (dose being exposed to, drugs or can think about environmental exposure)
3) the biology of the test organism
4) the chemical properties of a substance (if hydrophilic likely to diffuse through environment and get to the target)

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7
Q

what is toxicity like

A

non-linear dose-response relationship

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8
Q

what is maximal response in dose-response curves

A

may not be 100%, may never see 100% response, but will reach a threshold – no matter how much more you add

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9
Q

what is the dose-response curve

A

% response could be death, treatment etc

As response goes up is fairly linear till it tails off and then reaches a maximal response

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10
Q

what is NOAEL

A

No Observable Adverse Effect

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11
Q

what causes NOAEL

A

threshold

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12
Q

what is the NOAEL curve

A

no effect at start, then it starts to increase, then is linear then tails off again

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13
Q

what does the NOAEL tell us

A

how much is it safe to be exposed to before our body’s cannot tolerate it anymore, there will be a response

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14
Q

what is NOAEL

A

everything up to the point where there is a response

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15
Q

what response do we want biocides have

A

maximal response

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16
Q

when is a maximal level reached

A

when no further Adverse Effect is seen

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17
Q

what is needed to determine 50% effect

A

end point reached, graph can be used to determine point at which 50% effect is seen

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18
Q

what is LD50

A

50% of population is killed (Lethal Dose) (all dead)

LD50 the maximal response will be 100%, 50% of the population will be killed

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19
Q

what is TD50

A

50% of population shown unwanted (Toxic) effect (may have some surviours)

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20
Q

what is ED50

A

50% of population show desired effect (Effective)

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21
Q

what is maximal response set at

A

maximal response is set at 100%, but may not be all the population, is just where it plateaus

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22
Q

what is important to think about when giving dosages

A

Need to think about how much to give regards to the volume (body mass)

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23
Q

what are the phases in the toxic compound pathway

A

absorption
distribution
metabolism
excretion

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24
Q

what does absorption involve

A

passage across cell membranes whatever the route of entry into the organism

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25
Q

what are lipid membranes like

A

selectively permeable

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26
Q

what does passage of the chemical through the membrane depend on

A

size
lipid solubility
similarity to natural molecules (analogues)
polarity/charge

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27
Q

what are the ways foreign substances pass through a membrane

A

filtration through pores (size) (porins in bacteria)
passive diffusion through (lipid solubility)
active transport
facilitated diffusion

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28
Q

what uses facilitated diffusion

A

movement of toxin depends on charge/polarity – exchange transport where getting change in charge or polarity looking at facilitated diffusion

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29
Q

what process happens in multicellular organisms

A

phago/pinocytosis - engulfment of membrane vesicles and things taken inside cells, does usually happen in microbial populations, but is important in higher organisms

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30
Q

what is phago/pincyotosis independent of

A

independent of the chemistry e.g. size and charge is just whether or not you are taken up

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31
Q

what processes require receptors and are the basis of some biological variation

A

active transport

facilitated diffusion

32
Q

what may NOAEL be affected by

A

efficiency of:
- efflux pumps
- detoxification pathways
- excretion pathways
number of receptor sites (binding saturation)
varies depending on different types of cells

33
Q

which cells will absorb more molecules

A

cells with more receptor binding sites will take up more – difference in accumulation rates, difference in how much you tolerate before see an effect due to the variation of receptors

34
Q

what happens when the antibiotic e.g. streptomycin introduced into cell

A

if strep in cell quickly get resistance in population sue to single point mutation in a protein that makes up small subunit of ribosome - target site for strep to bind to
mutated strep can’t affect cell

35
Q

what is a downside of streptomycin in the cell

A

ribosome change due to preventing strep binding to target cell is that it is slightly worse at making protein

36
Q

what happens to the antibiotic resistant mutants when no antibiotic is present

A

mutants that are antibiotic resistant in the cell without antibiotic present will likely be outcompeted

37
Q

what happens to the antibiotic resistant mutants when the antibiotic is present

A

they survive and grow, population become antibiotic resistant

38
Q

what happens to microbial cells when microban/triclosan are added to plastic

A

leach out and contact with microbial cells
bacteria use an efflux pump it already had, up regulates it which leads to faster pumping of triclosan so cells become resistant

39
Q

why may microbe be resistant to molecules

A

molecule can go in at a standard rate, but have ability to pump it out, if have more pumps, can pump out faster

40
Q

what does the cell need if accumulate molecule

A

enzymes to detoxify it

41
Q

what effects the metabolising effect

A

how many enzymes you have

42
Q

which bacteria become resistant in metabolism

A

bacteria can gain enzyme that detoxifies an antibiotic

selected in population, cells with enzyme become resistant population

43
Q

how can excretion occur

A

urinary system
lungs
biliary system

44
Q

what is ADI

A

acceptable daily intake

45
Q

what is ADI based on

A

NOAEL

need to understand what the safe threshold is

46
Q

what is ADI used to determine

A

safe intake of food additives and contaminants

47
Q

what is the safety factor

A

built in depending on the severity of consequences of overexposure

48
Q

how is ADI calculated

A

NOAEL mgkg^-1day^-1 / 100*

* = safety factor

49
Q

what is dose

A

total amount administered

50
Q

what is dosage

A

includes reference to biological variation

e.g. body weight

51
Q

what is MEL

A

maximum exposure limit

52
Q

how are non-ingested compounds regulated

A

maximum exposure limit over 8h working day (to do with skin or inhaling)

53
Q

what is used as test organisms

A 
animals, commonly mice, rats, rabbits
aquatic organisms
invertebrates
bacteria 
cell culture systems
54
Q

what test is used to determine if a chemical is a mutagen

A

Ames Test

55
Q

what is the Ames test based on

A

assumption any substance that is mutagenic may also turn out to be a carcinogen

56
Q

what is a mutagen

A

agent capable of introducing mutations into DNA

57
Q

what is a carcinogen

A

agent resulting in the formation of cancer cells

58
Q

are all mutagens carcinogens

A

not all mutagens are carcinogens

59
Q

what bacterium is used in the Ames test

A

a strain of Salmonella enterica

60
Q

what is a phototroph

A

organism is able to grow on a medium lacking amino acid histidine (His)

61
Q

what is an auxotroph

A

strains carrying point mutations in a single gene in (His) biosynthesis pathway isolated
strains require His in medium for growth as can’t make it

62
Q

what are the point mutations in the different Ames strains

A

deletion
insertion
transition
transversion

63
Q

what is a back mutation

A

mutation reversed and regains its function

returns to be ableto grow

64
Q

what is prototrophy

A

be able to grow

65
Q

what happens in the Ames test

A

bacteria on petri dish test chemical disk in middle
only things that should grow is mutation
mutant can make own histidine and grow into colonies

66
Q

what is the filter paper soaked in

A

with known carcinogen (2-aminofluorine)

67
Q

what causes back mutations

A

mutagenic effect of the chemical

68
Q

what is the little clearing on the petri dish around the chemical disk in Ames test

A

DNA mutation that has occurred reversed mutation that we started with, but hasn’t caused lethal damage anywhere else in the cell
likely everything died as knocked out something essential as well

69
Q

what do colonies present in Ames test mean

A

first indication this is causing DNA damage

70
Q

what is usual to see in an Ames test petri dish

A

clear ring round chemical disk then a ring of mutations – more mutagenic more there will be
colonies outside ring area likely to be spontaneous mutations

71
Q

when can non mutagenic chemicals be converted to mutagens

A

converted into mutagens (and carcinogens) as they are metabolized

72
Q

what is the Ames test used for

A

first screen for possible carcinogenicity

73
Q

why is the Ames test good

A

simple

low cost

74
Q

what has been adapted since the Ames test

A

rapid in vitro tests have been adapted for some eukaryotic cells such as:
Strains of Yeast
Mouse or Human cells grown in culture

75
Q

what is a negative Ames test

A

only a few spontaneous revertants

Physiology of Microbes (21 decks)

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