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Medical Micro > lec 8-9 antibiotics > Flashcards

lec 8-9 antibiotics Flashcards

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USMLE® Step 1 flashcards
1
Q

bacteriostatic

A

stops bacteria from reproducing without killing them
inhibits protein synthesis
e.g. macrolides

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2
Q

bacteriocidal

A

kills bacteria

e.g. fluorouquinolones

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3
Q

bacteriolytic

A

destruction of bacteria by damaging their DNA or cell wall

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4
Q

broad spectrum antibiotics

A

act against a wide range of disease-causing bacteria including gram +ve and -ve

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5
Q

types of antibiotic

A

macrolides
fluoroquinolones
cephalosporins

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6
Q

macrolide structure

A

12-16 macrolactone rings with amino sugars attached

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7
Q

macrolide binding site

A

large 50S ribosomal subunit

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8
Q

macrolide functions

A

inhibit protein synthesis
if protein cannot exit via tunnel in ribosome, then translation is inhibited
leads to cellular growth and arrest

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9
Q

why are gram +ve bacteria difficult to target

A

thick peptidoglycan layer

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10
Q

fluoroquinolone structure

A

bicyclic core structure

bacteriocidal

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11
Q

fluoroquinolone function

A

targets DNA gyrase and Topoiosomerase IV
commonly used for urinary infections
causes irreversible damage

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12
Q

entry of fluoroquinolones into gram +/-ve bacteria

A

passive diffusion into gram +ve bacteria and via outer membrane porins in gram -ve

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13
Q

examples of fluoroquinolones

A

ciproflaxin

oxoflaxin

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14
Q

cephalosporins

A

broad spectrum
semi-synthetic beta-lactam antibiotic
derived from mould cephalosporium
chemically related to penicillins

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15
Q

function of cephalosporins

A

interfere with bacterial cell wall synthesis

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16
Q

clostridium difficile

A

pathogen that disrupts GI tract

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17
Q

dysbiosis

A

disruption of gut microbiota

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18
Q

bacteriophages as antimicrobials

A

use of phages (virus) to treat pathogenic bacterial infections

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19
Q

advantages of using bacteriophages as antimicrobials

A

specific

cheap

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20
Q

disadvantages of using bacteriophages as antimicrobials

A

narrow spectrum

bacterial resistance

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21
Q

stages of infection of bacteriophage into bacteria

A
  1. adsorption to specific receptor
  2. DNA injection
  3. peptidoglycan degradation - DNA transferred to cell
  4. redirection of host metabolism to phage DNA replication and phage protein sythesis
  5. assembly of phage particles
  6. bacterial cell lysis and phage progeny release
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22
Q

which bacteriophage late proteins are responsible for host cell lysis

A

lysins
holins
murein synthesis inhibitors

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23
Q

anti-virulence stratgies

A

inhibiti specific mechanisms
targeting toxins
inhibiting seccretion systems

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24
Q

UPEC mechanism

A

binds and invades cell
replicates inside cell and forms biofilm
biomass disperses and exits cell
spreads to new cells

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25
Q

synergistic effect

A

when interaction causes an increase in the effects of one or both of the drugs

26
Q

synergistic drugs

A

suppress drug-susceptible populations more the single-drug therapies

27
Q

antimicrobial resistance

A

resistance of a microorganism to an antimicrobial drug that was originally effective for treatment of infections caused by it

28
Q

2 methods to measure resistance

A

increase in minimum inhibitory concentration (MIC)

minimal bacterial concentration (MBC)

29
Q

minimum inhibitory concentration (MIC)

A

lowest concentration of antimicrobial that will inhibit visible growth of microorganism overnight

30
Q

limitation of MIC

A

micro bacteria takes 4 weeks to grow, too slow to change overnight

31
Q

minimum bactericidal concentration (MBC)

A

lowest concentration of an antimicrobial that will kill bacteria in vitro

32
Q

how do we know how much antibiotic to administer

A

break points

33
Q

break points

A

chosen concentration defining whether bacteria is susceptible or resistant to antibiotic

34
Q

if minimum inhibitory concentration (MIC) is more than the susceptibility break point…

A

.. then bacteria is intermediate or resistant to antibiotic

35
Q

if MIC is less than or equal to the susceptibility break point …

A

..then bacteria is susceptible to the antibiotic

36
Q

bacteriostatic agent

A

stops bacteria from reproducing

reaches MIC levels in blood/tissues

37
Q

bactericidal agent

A

kills bacteria

reaches cidal levels in blood/tissues

38
Q

broad spectrum agent

A

low MICs for many different bacteria types

  • very weak concentration of antimicrobial would kill many bacteria
39
Q

narrow spectrum agent

A

low MICs for just a few bacterial types

40
Q

susceptible (sensitive) microbe

A

inhibited by an agent at a low MIC

41
Q

resistance microbe

A

only inhibited by agents at a high MIC (takes higher dose to kill them)

42
Q

molecular mechanisms of resistance

A
  1. degradation of drugs by enzymes
  2. modification of drugs by enzymes
  3. alteration of drug target site
  4. drug efflux pumps
43
Q

beta-lactamase mechanism

A

degradation

break down beta lactam ring

e.g. cephalosporins - interfere in cell wall synthesis - bactericidal

44
Q

common antibiotic resistance

A

MRSA

45
Q

methicillin

A

in MRSA

is a beta-lactam antibiotic so broken down by beta-lactamases

46
Q

penicillin binding protein (PBP)

A

penicillin binding proteins join peptide bridges in peptidoglycan layer and facilitate cell wall synthesis

inhibited by beta-lactam antibiotics

47
Q

what prevents penicillin from binding to a protein

A

pencillin binding proteins bind to beta-lactam antibiotics, preventing cell wall synthesis
therefore lactam ring is broken down

48
Q

streptomycin

A

aminoglycoside

protein synthesis inhibitor
targets ribosome 30S subunit

modifies drug by phosphorylation

prevents drug from binding

49
Q

modifying membrane permeability of transport systems…

A

prevents entrance of drug into a cell

50
Q

drug efflux pumps

A

important for mediating resistance to many antibiotics
protein secretion system
rids of toxic products from inside cytoplasm to outside outer membrane

51
Q

RND family transporters

A

used by drug efflux pumps

powered by electrochemical gradient

52
Q

transposons

A

transposable elements
can change their position within a genome
can create or reverse mutations and alter a cell’s genetic identity
mediators of resistance

53
Q

vertical gene transfer

A
  • spontaneous mutant resistant strain
  • apply antibiotic and only
    individual resistant strain will survive and reproduce
  • all susceptible bacteria will die
  • you have to wait for selection pressure (antibiotic) to occur
54
Q

horizontal gene transfer

A
  • transfer of genetic material between mature cells
  • no increase in number of cells but increase in number of resistance cells
  • transformation, conjugation and transduction
55
Q

spread of antibiotic resistance genes

A

horizontal and vertical gene transfer

56
Q

transformation

A

manipulation of a bacteria enabling it to take up DNA
protein secretion system (type 6) used to kill surrounding cells and uptake their DNA
natural transformation mediated by competence proteins

57
Q

conjugation

A

resistance gene moves with replicating plasmid into a new cell (no replication involved)

58
Q

transduction

A

resistance gene hijacks and integrates host cell plasmid with bacteriophage DNA

59
Q

R plasmids

A

important in resistance

have genes for conjugation fertility factor

60
Q

conjugation plasmid

A

a plasmid that is transferred from one bacterial cell to another during conjugation.

61
Q

conjugation fertility factor

A

allows genes to be transferred from a bacterium carrying the factor to a bacterium lacking the factor by conjugation

62
Q

origin of transfer

A

short sequence of genes necessary for DNA transfer from bacterial hst to recipient during bacterial conjugation

cis acting - oriT is found on same DNA that is transferred

Medical Micro (10 decks)

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