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Physiology of Microbes > Toxicity and Ames L20 > Flashcards

Toxicity and Ames L20 Flashcards

(75 cards)

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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
what are lipid membranes like
selectively permeable
26
what does passage of the chemical through the membrane depend on
size lipid solubility similarity to natural molecules (analogues) polarity/charge
27
what are the ways foreign substances pass through a membrane
filtration through pores (size) (porins in bacteria) passive diffusion through (lipid solubility) active transport facilitated diffusion
28
what uses facilitated diffusion
movement of toxin depends on charge/polarity – exchange transport where getting change in charge or polarity looking at facilitated diffusion
29
what process happens in multicellular organisms
phago/pinocytosis - engulfment of membrane vesicles and things taken inside cells, does usually happen in microbial populations, but is important in higher organisms
30
what is phago/pincyotosis independent of
independent of the chemistry e.g. size and charge is just whether or not you are taken up
31
what processes require receptors and are the basis of some biological variation
active transport | facilitated diffusion
32
what may NOAEL be affected by
efficiency of: - efflux pumps - detoxification pathways - excretion pathways number of receptor sites (binding saturation) varies depending on different types of cells
33
which cells will absorb more molecules
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
what happens when the antibiotic e.g. streptomycin introduced into cell
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
what is a downside of streptomycin in the cell
ribosome change due to preventing strep binding to target cell is that it is slightly worse at making protein
36
what happens to the antibiotic resistant mutants when no antibiotic is present
mutants that are antibiotic resistant in the cell without antibiotic present will likely be outcompeted
37
what happens to the antibiotic resistant mutants when the antibiotic is present
they survive and grow, population become antibiotic resistant
38
what happens to microbial cells when microban/triclosan are added to plastic
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
why may microbe be resistant to molecules
molecule can go in at a standard rate, but have ability to pump it out, if have more pumps, can pump out faster
40
what does the cell need if accumulate molecule
enzymes to detoxify it
41
what effects the metabolising effect
how many enzymes you have
42
which bacteria become resistant in metabolism
bacteria can gain enzyme that detoxifies an antibiotic | selected in population, cells with enzyme become resistant population
43
how can excretion occur
urinary system lungs biliary system
44
what is ADI
acceptable daily intake
45
what is ADI based on
NOAEL | need to understand what the safe threshold is
46
what is ADI used to determine
safe intake of food additives and contaminants
47
what is the safety factor
built in depending on the severity of consequences of overexposure
48
how is ADI calculated
NOAEL mgkg^-1day^-1 / 100* | * = safety factor
49
what is dose
total amount administered
50
what is dosage
includes reference to biological variation | e.g. body weight
51
what is MEL
maximum exposure limit
52
how are non-ingested compounds regulated
maximum exposure limit over 8h working day (to do with skin or inhaling)
53
what is used as test organisms
``` animals, commonly mice, rats, rabbits aquatic organisms invertebrates bacteria cell culture systems ```
54
what test is used to determine if a chemical is a mutagen
Ames Test
55
what is the Ames test based on
assumption any substance that is mutagenic may also turn out to be a carcinogen
56
what is a mutagen
agent capable of introducing mutations into DNA
57
what is a carcinogen
agent resulting in the formation of cancer cells
58
are all mutagens carcinogens
not all mutagens are carcinogens
59
what bacterium is used in the Ames test
a strain of Salmonella enterica
60
what is a phototroph
organism is able to grow on a medium lacking amino acid histidine (His)
61
what is an auxotroph
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
what are the point mutations in the different Ames strains
deletion insertion transition transversion
63
what is a back mutation
mutation reversed and regains its function | returns to be ableto grow
64
what is prototrophy
be able to grow
65
what happens in the Ames test
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
what is the filter paper soaked in
with known carcinogen (2-aminofluorine)
67
what causes back mutations
mutagenic effect of the chemical
68
what is the little clearing on the petri dish around the chemical disk in Ames test
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
what do colonies present in Ames test mean
first indication this is causing DNA damage
70
what is usual to see in an Ames test petri dish
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
when can non mutagenic chemicals be converted to mutagens
converted into mutagens (and carcinogens) as they are metabolized
72
what is the Ames test used for
first screen for possible carcinogenicity
73
why is the Ames test good
simple | low cost
74
what has been adapted since the Ames test
rapid in vitro tests have been adapted for some eukaryotic cells such as: Strains of Yeast Mouse or Human cells grown in culture
75
what is a negative Ames test
only a few spontaneous revertants

Physiology of Microbes (21 decks)

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