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Pathology > Microbiology - Antimicrobials 1 > Flashcards

Microbiology - Antimicrobials 1 Flashcards

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1
Q

when do most antibiotics work?

A

when the cell is active i.e. when bacteria is dividing

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2
Q

what are the 3 selective targets for antimicrobials?

A
  • peptidoglycan layer of cell wall
  • inhibition of bacterial protein synthesis
  • DNA gyrase and other prokaryote enzymes
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3
Q

which antibiotics inhibit cell wall synthesis?

A

beta-lactams

glycopeptides

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4
Q

name some beta-lactam antibiotics

A

penicillin
cephalosporin
carbapenems
BROAD SPECTRUM

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5
Q

name some glycopeptides

A

vancomycin
teicoplanin
GRAM POSITIVE

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6
Q

describe the gram positive cell wall

A

thick peptidoglycan cell wall

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7
Q

describe the gram negative cell wall

A

thinner peptidoglycan cell wall
outer membrane conferring resistance to some antibiotics
can be more resisitant and harder to treat due to outer membrane

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8
Q

what is the moa of beta lactams?

A
  • inactivate enzymes involved in terminal stages of cell wall synthesis (transpeptidases/ pencillin binding proteins)
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9
Q

when are beta lactams ineffective?

A
  • if cell wall has already been formed

- ineffective against bacteria lacking peptidoglycan cell walls (mycoplasma, chlamydia)

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10
Q

when is penicillin used?

A

gram +ve, streptococci, clostridia

broken down by beta lactamase

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11
Q

when is amoxicillin used?

A 
broad spectrum (enterococci to gram -ve)
broken down by beta lactamase
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12
Q

when is flucloxacillin used?

A

staph aureus
not broken down by beta lactamase produced by SA
similar to penicillin
less reactive

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13
Q

when is piperacillin used?

A 
broad spectrum (pseudomonas, non-enteric gram -ve)
- broken down by beta lactamase
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14
Q

what does clavulanic acid used?

A

as part of co-amoxiclav

it is a beta lactamase inhibitor so protects penicillin from enzymatic breakdown

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15
Q

what is tazobactam made up of?

A

tazocin and piptazobactam

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16
Q

name some cephalosporins

A
  • cefuroxime
  • ceftriaxone
  • ceftazidime
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17
Q

what cover does cefuroxime provide?

A
  • stable to many beta lactamases made by gram -ve
  • similar cover to co-amox
  • less active against anaerobes (add metronidazole)
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18
Q

what cover does ceftriaxone provide?

A
  • associated with C difficile
  • treat meningitis
  • no cover against pseudomonas
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19
Q

what cover does ceftazidime provide?

A

pseudomonas

HAIs often

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20
Q

what antibiotics do you use in ESBL producing organisms that are resistant to cephalosporins?

A

carbapenems

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21
Q

name some carbapenems

A
  • meropenem
  • imipenem
  • ertapenem
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22
Q

what cover do carbapenems provide? when used?

A

broad spectrum

stable to ESBL enzymes

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23
Q

what are the key features of beta lactams?

A
  • relatively non toxic
  • renally excreted so dec dose if renal impairment
  • short half life
  • ## won’t cross BBB
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24
Q

when are glycopeptides used?

A

gram +ve

inhibit cell wall synthesis

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25
what are important uses of glycopeptides?
- MRSA infections | - C. difficile infections
26
name the broad antibiotic categories that inhibit protein synthesis
- aminoglycosides - tetracyclines - macrolides - chloramphenicol - oxazolidinones (linezolid)
27
name some aminoglycosides
- gentamicin - amikacin - tobramycin
28
moa of aminoglycosides
- bind to 30S ribosome subunit - rapid concentration dependent bactericidal - ototoxic and nephrotoxic so monitor levels
29
which are active against pseudomonas?
gentamicin | tobramycin
30
how do aminoglycosides react with beta lactams?
synergistic combination | used in endocarditis treatment, pneumonia
31
what is the moa of tetracyclines?
- reversibly bind to 30S ribosome unit - prevent binding of aminoacyl-tRNA to ribosomal acceptor site - inhibits protein synthesis
32
what are tetracyclines active against?
chlamydia rickettsia mycoplasma
33
what are the problems with tetracyclines?
- now widespread resistance - deposited in growing bone (don't give to children, pregnant women) - SE: photosensitivity rash
34
name some macrolides
erythromycin clindamyxin clarithromycin azithromycin
35
moa of macrolides
- bind to 50s subunit of ribosome - interfere with translocation - stimulate dissociation of peptidyl-tRNA
36
what are macrolides used against?
- active against campylobacter, legionella, pneumophilia - useful for staph/ strep in pen-allergic patients - little activity against gram-ve
37
moa of chloramphenicol
- binds to peptidyl transferase of 50S ribosomal subunit | - inhibits formation of peptide bonds during translation
38
when is chloramphenicol used?
if pen- allergic, used for meningitis | eye preparations
39
why is chlorampenicol rarely used?
- risk of aplastic anaemia | - risk of grey-baby syndrome in neonates
40
moa of oxazolidinones
binds to 23S component of 50S subunit | prevents formation of a functional 70S initiation complex
41
what are oxazolidinones used against?
against gram +ve (MRSA, VRE) | not active against gram -ve
42
what are the disadvantages of oxazolidinones?
- expensive | - may cause thrombocytopaenia and optic neuritis
43
what are the antibiotics that inhibit DNA synthesis?
- quinolones/fluoroquinolones | - nitroimidazoles
44
name some quinolones
ciprofloxacin levofloxacin moxifloxacin
45
how do quinoloes work?
act on alpha unit of DNA gyrase
46
what are the advantages of quinolones?
broad antibacterial activity | well absorbed orally (good bioavailability)
47
what are the advantages of quinolones?
UTI pneumonia atypical pneuomina bacterial gastroenteritis
48
name some nitroimidazoles
metronidazole | tinidazole
49
what is the moa of nitrioimidazoles
under anaerobic conditions, an active intermediate is produced this causes DNA strand breakage
50
uses of nitrioimidazoles
active against anaerobic bacteria
51
what antibiotics inhibit RNA synthesis
rifampicin and rifabutin
52
how do rifamycins work?
- inhibit protein synthesis by binding to DNA-dependent RNA polymerase
53
use of rifamycins
active against mycobacteria and chlamydia
54
what are important things to remember with rifamycins?
interactions with other drugs metabolised in liver (e.g. OCP) need to monitor LFTs turns secretions orange
55
which antibiotics interfere with cell membrane toxins?
- daptomycin | - colistin
56
name the antibiotics that inhibit folate metabolism
- sulphonamides (e.g. sulphamethoxazole) | - diaminopyrimidines (e.g. trimethoprim)
57
what is co-trimoxazole? when is it used?
- sulphamethoxazole and trimethoprim - synergisitc action between 2 drug classes because they act on sequential steps in same pathway - used in PCP
58
what are the different mechanisms of resistance?
BEAT 1. Bypass antibiotic sensitive step 2. Enzyme chemical modification/ inactivation of antibiotic (ESBLs) 3. Accumulation reduced of antibiotic (Impaired uptake = doxycycline, enhanced efflux = flucytosine) 4. Target modification or replacement (MRSA, flucloxicillin, macrolides)
59
which antibiotics are affected by inactivation by microbes?
beta lactams aminoglycosides chloramphenicol
60
which antibiotics are affected by microbes altering the target?
``` beta lactams macrolides quinolones rifampicin chloramphenicol linezolid glycopeptides ```
61
which antibiotics are affected by reduced accumulation?
``` tetracyclines beta lactams aminoglycosides quinolones chloramphenicol ```
62
which antibiotics are affected by the antibiotic sensitive step being bypassed?
trimethoprim | sulphonamides

Pathology (21 decks)

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