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Z MD1 Cardiac physiology > antibiotics > Flashcards

antibiotics Flashcards

1
Q

likely causative organsims for otitis media and sinusitis

A

strep pneumoniae, H. influenzae - amoxycillin

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2
Q

two mechanisms of drug inactivation causing resistance to antimicrobial agents

A
  • hydrolysis - eg. pseudomonas aeroginosa produces beta-lactamase - hydrolysing beta-lactam antibiotics - covalent modification - eg. modification of aminoglycosides
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2
Q

2 ways to create resistance in bacteria

A

intrinisic acquired (mutation or horizontal gene transfer)

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2
Q

antimicrobial agents that act on cell wall

A

beta lactams, glycopeptides

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3
Q

how are the MIC and the zone of antibiotic clearance diameter related?

A

the bigger the zone diameter the lower the MIC

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4
Q

tobramycin active against

A

pseudomonas aeroginosa

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4
Q

examples of altering the target of drug action by micro-organsims

A
  • modify target to less sensitive form - B-lactam (altered PBP), and vancomycin (sugar instead of D-ala)
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5
Q

flucloxacillin used to treat which type of bacteria

A

staphyloccus - low toxicity

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5
Q

what is the synergistic effect when combining 2 antibiotics together?

A

when you add the 2 drugs together you get an unexpected positive benefit

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6
Q

How does the E-test strip work?

A

another type of diffusion test - log scale of two fold dilution on a piece of filter paper

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6
Q

what is the antagonistic effect when combining 2 antibiotics together?

A

the two drugs interfere with each other - get a worse outcome compared with either of them by themselves

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6
Q

examples of reducing access of drug to target by micro-organisms

A

-reduced entry into cell - aminoglycosides -increased efflux from cell - aminoglycosides, tetracycline

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7
Q

how does the disc susceptibility test work?

A

discs of antibiotics placed into a culture of micro-organism - see if there are rings of no growth

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7
Q

what is the mechanism of the synergistic effect of antibiotic combinations?

A
  • they block sequential steps of a metabolic pathway - inhibit enzymatic degredation - enhance antimicrobial uptake by bacterial cells
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8
Q

3 types of horizontal transfer

A

transformation phage mediate transduction plasmid-mediated conjugation

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9
Q

what is the indifferent effect when combining 2 antibiotics together?

A

on their own the antibiotics have an effect when adding them together - they have a better effect, however this could have just been achieved by increasing the concentration of one of the antibiotics

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11
Q

how are antimicrobial agents classified?

A

source: natural or synthetic broad mechanism of action

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11
Q

how is aminoglcoside resistance achieved

A
  1. modified outer membrane causing reduced entry 2. enzymatic modification causing reduced entry (acetylation, adenylation, phosphorylation, adenylation phosphorylation) 3. ribosomal mutation - reduces binding
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11
Q

antimicrobial agents that act on cytoplasmic membrane

A

polymyxins, polyenes

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12
Q

why to transpeptidases bind to beta-lactams?

A

recognise the beta-lactam ring as similar to the bond between terminal D-ala amino acids

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13
Q

how is beta-lactam resistance achieved?

A

1) beta lactamases - acts on beta-lactam ring and hydrolyses it 2) altered PBP - makes something beta-lactams will bind to but does not interfere with cross linking

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14
Q

how do you determine the MIC using the E test

A

where the clear zone edge intersects this piece of paper = MIC

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15
Q

What is the micro-organism that changes the terminal D-ala so vancomycin cant bind?

A

enterococci

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16
Q

why are semi-synthetic drugs useful?

A

you can alter the pharmacological properties of antibiotics to suit use - change kinetics - reduce toxicity - modify antimicrobial spectrum

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16
Q

what are the 2 effects anti-microbial agents can have

A

bacteriostatic bactericidal

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18
Q

how can vancomyin resistance be achieved

A

bacterium replaces the terminal D-ala with a sugar and so vancomycin cant bind strongly

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20
Q

carbenicillin important for which organism?

A

pseudomonas aeruginosa

21
Q

what is the micro-organism that overproduces the peptidoglycan wall so vancoymycin cant bind?

A

staphlococcus aureus

22
Q

methicillin used to treat which type of bacteria

A

staphyloccus - moderate toxicity (nephrotoxic)

23
Q

how is peptidoglycan cross-linking achieved

A

transpeptidase enzymes catalyse the cross linking by removing the terminal D-ala from the precursor peptidoglycan

23
Q

what is plasmid-mediated conjugation

A

formation of sex pillus (cytoplasmic bridge) replication and transfer of DNA plasmid across bridge and recombination

24
Q

metranidozole only acts on…

A

strict anaerobes

25
Q

examples of drug inactivation by micro-organisms

A

hydrolysis - B-lactams covalent modification - aminoglycoside

27
Q

difference between penicillin G and penicillin V

A

penicillin G was destroyed in the stomach as so had to be given by injection penicillin V acid stable - able to be taken orally

29
Q

gentomycin active against

A

lots of gram -ve bacteria

30
Q

what are the mechanisms for antagonism

A
  • inhibition of the bactericidal activity by a bacteriostatic agent - induction of enzymatic degredation - competition for binding to the same target - inhibition of target
31
Q

likely causative organsims for UTI, cystitis

A

>80% E coli - cephalexin or co-amoxyclav or trimethoprim

33
Q

bonus of using ampicillin compared to penicillin G

A

ampicillin can also treat gram negative rods (penicillin G could not)

35
Q

MRSA - resistant to which antibiotics

A

all beta-lactam antibiotics

36
Q

2 mechanisms of altering target of drug action to cause resistance to antimicrobial agents

A
  1. modify target to a less sensitive form - eg. MRSA - altered PBP for beta-lactam. eg. VRSA - put sugar instead of D-ala at end of peptidoglycan precursor 2. overproduction of target - eg. overproduce peptidoglycan in staph aureas- soaks up vancomycin
37
Q

what is transformation

A

donor bacterium lysis - fragments of DNA DNA uptake by competent cells homologous recombination4 (must be between closely related bacteria)

37
Q

antimicrobial agents that act on folic acid

A

sulphonamides, trimethoprim

38
Q

likely causative organsims for a sore throat and the antibiotic of choice

A

>50% viral - no antibiotic strep pyogenes - penicillin

39
Q

examples of failure to inactivate inactive precursor of drug

A

metronidazole isoniazid

41
Q

targets for antimicrobial agents

A

cell wall - beta lactams, glycopeptides cytoplasmic membrane - polymyxins, polyenes ribosomes - aminoglycosides, chloramphenicol nucleic acid - rifamycins, quinolones folic acid - sulphonamides, trimethoprim

42
Q

what are the types of anti-microbial agents

A

antibiotics - naturally occurring chemotherapeutic agents - synthetic semi-synthetic

43
Q

action of aminoglycosides

A

bind to 30s ribosome of bacterium - distorts the reading frame for transcription –> introduces abnormal amino acid or stops transcription completely

44
Q

likely causative organsims for skin infection

A

staph aureus or strep pyogenes - penicillin, mupirocin, dicloxacillin

45
Q

action of ticarcillin

A

resistant to chromosmal encoded beta-lactamse

46
Q

antimicrobial agents that act on ribosomes

A

aminoglycosides, chloramphenicol

47
Q

what does phage mediated transduction have the potential to do to cause a epidemic pathogen?

A

could transfer R between staph epidermis and staph aureas

48
Q

2 mechanisms to reduce access of drug to target to cause resistance to antimicrobial agents

A
  1. decrease entry into cells - eg. R to aminoglycosides 2. increased efflux from cell - eg. aminoglycosides, tetracyline
50
Q

action of beta-lactam antibiotics

A

binds to transpeptidases directly -> suicide inhibition -> stops the formation of cross linking of peptidoglycans for cell wall

52
Q

How does the dilution method work for antibiotic susceptibility testing?

A

series of test tubes with different concentration of antibiotics - do a two fold dilution across the tubes with growth medium in it. Then add micro-organism and incubate overnight. Look for the lowest conc that inhibits the growth of the organism

53
Q

action of clavulonic acid

A

resistant to plasmid encoded but not chromosmal encoded beta-lactamse

55
Q

basic structure of beta-lactam antibiotics

A

5 carbon chain ring with 4 carbon chain ring. Joined together by a N and with a double bonded oxygen to the 4 C ring. They differ in the substitution in the 5 C ring and whether they have a single or double bond in the 5 C ring

56
Q

two main methods for antibiotic susceptibility testing

A

dilution methods diffusion methods

57
Q

How do you determine the MIC?

A

the lowest antibiotic concentration that prevents micro-organism growth (first clear tube)

58
Q

antimicrobial agents that act on nucleic acid

A

rifamycins, quinolones

60
Q

what are the 3 types of effects you can get when combining 2 antibiotics

A

indifference antagonism synergy

61
Q

Action of vancomycin

A

binds to terminal D-ala of peptidoglycan precursor stopping the action of transpeptidase

62
Q

example of failure to activate inactivate precursor of drug to cause resistance to antimicrobial agents

A

metronidazole - only activated in strict anaerobic bacteria some myco TB dont have the Kat enzyme to convert it to its active form and therefore are Resistant

63
Q

what kind of bacteria can vancomycin act on

A

only acts on gram positive bacteria (cannot pass through outer lipid membrane of gram negative bacteria)

64
Q

what is phage mediated transduction?

A

infection of recipient cell with abnormal phage with R genes encoded –> recombination into chromosome

65
Q

what does transformation have the potential to do to cause a epidemic pathogen

A

transfer antibiotic R from commensals to pathogens

66
Q

likely causative organsims for an acute exacerbation of chronic bronchitis

A

H. influenzae or strep pneumoniae - treat with amoxycillin or doxycyciline

Z MD1 Cardiac physiology (13 decks)

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