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Microbiology - Quiz 2 > Antibiotics > Flashcards

Antibiotics Flashcards

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1
Q 
Mupirocin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Translation inhibitor
Binds isoleucyl-tRNA synthetase, so no charged ile-tRNA available
Bacteriostatic at low concentrations, cidal at higher (with topical administration)
Used in surgeons to prevent transmission of MRSA from nasal cavity

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2
Q 
Ciprofloxacin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Fluoroquinolone (DNA replication inhibitor)
Inhibits DNA gyrase and thus DNA synthesis
Bacteriocidal
Broad spectrum: Gm- enterics, G+ cocci, Pseudomonas
Resistance emerging
Not for kids or pregnant women

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3
Q 
Moxifloxacin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Fluoroquinolone (DNA replication inhibitor)
Inhibits DNA gyrase AND topoisomerase activity (less susceptible to resistance)
Bacteriocidal
Broad spectrum: Gm- enterics, G+ cocci, Pseudomonas, MRSA
Not for kids or pregnant women

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4
Q 
Metronidazole:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Nitroimidazole (DNA replication inhibitor)
Activated form (in anaerobic conditions) binds DNA and fragments it
Bacteriocidal
Useful against anaerobic bacterial, protozoa

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5
Q 
Rifampin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

RNA synthesis inhibitor
Binds beta subunit of RNA pol, inhibiting transcription
Bacteriocidal
Broad spectrum
Effective prophylactic against N. menigitidis b/c secreted in saliva
Resistance develops rapidly, used in combo

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5
Q

Example of antagonistic combined antibiotic action

A

Penicillin (requires growth) given with bacteriostatic agent (tetracycline)

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6
Q 
Ethambutol and pyrazinamide:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A 
Anti TB drugs
Unknown mechanism of action
E- static, P- cidal once activated
Narrow spectrum (TB)
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7
Q

Example of synergistic combined antibiotic action

A

Agent which damages cell wall/membrane with cidal agent taken up poorly by bacterium

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8
Q

Indications for combined use of antibiotics (5)

A 
Synergistic activity expected
Pathogen requires more than one agent
Likelihood of resistance reduced
Dosage of toxic drug can be reduced
Polymicrobial infection requires use of more than one agent
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9
Q

Disadvantages of combined antibiotics (4)

A

Increased risk of side effects
Increased risk of superinfections
Possible antagonism
Increased cost

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10
Q

4 general reasons for antibiotic inactivity

A
  1. Enzyme inactivation: antibiotic is inactivated (extracellular, intracellular, both)
  2. Altered membrane permeability/antibiotic efflux: antibiotic can’t enter cell or is actively pumped out
  3. Alteration of ribosomal/cell wall precursor/enzyme targets: bacterial cell contains altered enzyme that resists action of antibiotic
  4. Bypass pathways: antibiotic enters cell but drug-binding target site is replaced
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11
Q

Mechanisms of resistance to trimethoprim

A

Plasmid-coded, trimethoprim-resistant dihydrofolate reductase

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12
Q

Mechanisms of resistance to penicillins (3)

A

Hydrolysis of beta-lactam ring by beta-lactamase
Decreased cephalosporins permeability of bacteria
Altered penicillin binding proteins

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13
Q

Mechanisms of resistance to methicillin

A

Altered penicillin binding proteins

Beta-lactamase resistant

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14
Q

Mechanisms of resistance to aminoglycosides (3)

A

Enzymatic modification of drug by plasmid-coded enzyme
Decreased permeability to antibiotic
Altered antibiotic binding site

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15
Q

Mechanisms of resistance to tetracyclines

A

Interference with transport of drug into cell

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16
Q

Mechanisms of resistance to chloramphenicol

A

Detoxification of drug by acetylation of hydroxyl

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17
Q

Mechanisms of resistance to erythromycin

A

Enzymatic methylation of 23S ribosomal RNA

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18
Q

Mechanisms of resistance to ciprofloxacin/rifampin

A

Altered target enzymes (gyrase, RNAP)

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20
Q

Mechanisms of resistance to vancomycin

A

Alteration of cell wall precursor target

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21
Q

Characteristics of an ideal antibiotic (4)

A

Target one or more bacterial species with no toxicity or allergy
Persist long enough to destroy target
Not lose effectiveness due to bacterial resistance
Achieve effective concentrations in sites of infection

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22
Q

Define bacteriostatic

A

Stops growth of bacteria for a time

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23
Q

Define bacteriocidal

A

Kills bacteria

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24
Q

What is the Kiby-Bauer disc diffusion method? How does it work?

A

Allows you to test the sensitivity of multiple antibiotics against a given strain

Plate purified bacteria on agar plate
-> Add filter paper discs with antibiotic onto the surface
-> Measure circular zones of inhibition of bacterial growth around each disc
(inhibition = sensitivity, growth = insensitivity)

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25
Q

How can you test for beta-lactamase production?

A

Plate bacteria on nitrocefin, which is chromogenic and has a beta-lactam ring sensitive to hydrolysis

26
Q

What is the MIC? How can you test for it?

A

MIC = minimum inhibitory concentration

Inoculate tubes with same amount of bacteria
Add serial dilution of antibiotic
MIC= lowest amount of antibiotic needed to inhibit growth

27
Q

What is MBC? How can you test for it?

A

MBC = minimum bacteriocidal concentration

Perform MIC test, then plate bacteria in absence of antbiotic to see if they grow or if they were killed by antibiotic

28
Q

Define antimetabolite.

A

Interferes with the synthesis or function of a substance involved in normal cell metabolism
Often structurally similar to the natural substance

29
Q 
Sulfonilamide:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
A 
Sulfonamide (antimetabolite)
Inhibits synthesis of folic acid -> lack of DNA synthesis
Bacteriostatic
Broad range of species
Used for UTIs (concentrated in urine)
30
Q 
Trimethoprim:
Class?
Action?
Bacteriostatic/cidal?
Application?
A

Antimetabolite
Inhibits later step in folic acid metabolism (dihydrofolate reductase = present in humans, but much higher affinity for bacterial enzyme)
Bacteriostatic
Used for UTIs

31
Q 
Bactrim:
Class?
Action?
Bacteriostatic/cidal?
Application?
A

Antimetabolite
Combination of sulfamethoxazole and trimethoprim for a synergistic effect
Bacteriostatic
Used for UTIs

32
Q 
Isoniazid:
Class?
Action?
Bacteriostatic/cidal?
Species range?
A

Antimetabolite
Inhibits synthesis of mycolic acid, found in the cell walls of mycobacteria
Bacteriocidal
Narrow - specific to M tuberculosis
Efficient cellular penetration (intracellular)

33
Q

Penicillins: why the large difference in sensitivity between bacterial and animal cells?
Bacteriostatic or bacteriocidal?
What conditions are required?

A

Difference in sensitivity because there is no cell wall in animal cells
Bacteriocidal
Growth is essential for action - inhibit peptidoglycan synthesis

34
Q

Basic structure of penicillins. What are they sensitive to? (2 things)

A

Have beta-lactam and thiazolidine rings

Sensitive to hydrolysis by stomach acids and beta-lactamases

35
Q

Mechanism of action of penicillins

A

Beta-lactam = structural analog of peptidoglycan pentapeptide - bind to and inactive penicillin-binding proteins (PBPs): transpeptidases that are responsible for cross-linking (the final step in cell wall assembly)

36
Q 
Penicillin G:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A 
Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Ineffective against Gm- enterics
Acid-labile - cannot be taken orally
Sensitive to beta-lactamases
37
Q 
Penicillin V:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A 
Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Ineffective against Gm- enterics
Resist acid hydrolysis - can take orally
Sensitive to beta-lactamases
38
Q 
Ampicillin/amoxicillin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A

Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Broader spectrum: effective against Gm- enterics
Resist acid hydrolysis - can take orally
Sensitive to beta-lactamases

Amoxicillin = higher serum levels

39
Q 
Tricarcillin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A

Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Extended spectrum - effective against Gm- enterics and Pseudomonas aeruginosa
Sensitive to beta-lactamases

40
Q 
Piperacillin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A

Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Extended spectrum - the most active penicillin against Gm- enterics and Pseudomonas aeruginosa
Sensitive to beta-lactamases

41
Q 
Methicillin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A

Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Narrow spectrum - antistaphylococcal! for resistant staph
Resistant to beta-lactamases
Acid-labile - cannot be taken orally

42
Q 
Oxacillin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Application?
Sensitivity?
A

Penicillin (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Narrow spectrum - antistaphylococcal! for resistant staph
Resistant to beta-lactamases
Resist acid hydrolysis - can take orally

43
Q 
Cefazolin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
A

Cephalosporin (beta-lactam antibiotic, cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Most active versus Gm+ cocci and some Gm- enterics

44
Q 
Cefuroxime:
Class?
Action?
Bacteriostatic/cidal?
Species range?
A

Cephalosporin (beta-lactam antibiotic, cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Most active versus Gm- enterics, less effective against Gm+

45
Q 
Ceftriaxone/ceftazidime:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Sensitivity?
A

Cephalosporin (beta-lactam antibiotic, cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Very broad spectrum, active against P. aeruginosa
Increased beta-lactamase resistance

46
Q

Differences between cephalosporins and penicillins (5, 2 similarities)

A

Both have beta-lactam rings
Both bacteriocidal

Cephalosporins:
Have dihydrothiazine vs thiazolidine ring
Generally broader spectrum
Greater acid stability
Resist some beta-lactamases
Good for penicillin allergies (antigenically dissimilar)

47
Q 
Aztreonam:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Sensitivity?
A

Monobactam (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Specific to Gm- aerobes including P. aeruginosa
Resistant to beta-lactamases
Minimal cross-immunogenicity with other beta-lactams

48
Q 
Imipenem:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Sensitivity?
A 
Carbapenem (cell wall synthesis inhibitor)
Inhibits penicillin-binding proteins
Bacteriocidal
Broadest spectrum
Resistant to beta-lactamases
Susceptible to renal dispeptidase
49
Q

What s a beta-lactamase inhibitor? Name two.

A

Beta-lactams which have minimal activity as antibiotics but extend the use of beta-lactam antibiotics

Clavulanic acid (used with amoxicillin -> augmentin)
Sulbactam
50
Q 
Vancomycin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Glycopeptide cell wall synthesis inhibitor
Binds R-D-Ala-D-Ala - blocks peptidoglycan precursor transfer
Bacteriocidal
Restricted to Gm+
Toxic - used for MRSA and multiply resistant enterococcus
VRSA now identified

51
Q 
Cycloserine:
Class?
Action?
Bacteriostatic/cidal?
Species range?
A

Cell wall synthesis inhibitor
Inhibits D-alanine steps
Bacteriocidal
Secondary tuberculosis drug

52
Q 
Bacitracin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A 
Cell wall synthesis inhibitor
Inhibits lipid carrier step
Bacteriocidal
Restricted to Gm+
Toxic - used for topical therapy
53
Q 
Polymyxin B:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Cell membrane permeabilizer
Bind LPS, then membrane phospholipids, leading to membrane leakage
Bacteriocidal (does NOT require growth)
Selective for Gm- enteric rods, esp. Pseudomonas
Toxic, so topical only

54
Q 
Streptomycin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Aminoglycoside (translation inhibitor)
Binds 30S subunit, distorts acceptor site -> misreading -> bad proteins -> leaky membranes
Bacteriocidal due to membrane effects
Inhibited by anaerobic or acidic conditions
Not good for urine
Toxic!

55
Q 
Gentamicin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Aminoglycoside (translation inhibitor)
Binds multiple sites on the 30S subunit (less resistance) -> leaky membranes
Bacteriocidal due to membrane effects
Inhibited by anaerobic or acidic conditions
Toxic!

56
Q 
Tetracycline/doxycycline/minocycline:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A 
Tetracyclines (translation inhibitors)
Block binding of aminoacyl tRNA to 30S
Bacteriostatic
Broad spectrum, also useful for intracellular parasites
Not used for pregnancy or young children
Wipe out normal flora
57
Q 
Erythromycin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A 
Macrolide (translation inhibitor)
Blocks chain elongation
Bacteriostatic
Broad spectrum, includes mycoplasma and chlamydia
Widely used
58
Q 
Azithromycin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A 
Macrolide (translation inhibitor)
Blocks chain elongation, but higher tissue concentrations than erythromycin
Bacteriostatic
Slightly larger range than erythromycin
Widely used
59
Q 
Chloramphenicol:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Translation inhibitor
Blocks chain elongation
Bacteriostatic, can be cidal
Used for anaerobes, particularly enterics
Not widely used because of toxicity (lethal aplastic anemia)

60
Q 
Clindamycin:
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Translation inhibitor
Inhibits peptidyl transfer
Bacteriostatic
Active against Gm+, especially active against anaerobes

61
Q 
Dalfopristin/quinupristin [Synergin]
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Streptogramins (translation inhibitors)
Bind to 50S subunit
Bacteriostatic
Useful against resistant bacteria, especially because of synergistic combination

62
Q 
Linezolid (Zyvox):
Class?
Action?
Bacteriostatic/cidal?
Species range?
Applications?
A

Oxazolidinone (translation inhibitor)
Interacts with 16S and 23S rRNA, inhibit tRNA translocation
Bacteriostatic
Useful against resistant bacteria

Microbiology - Quiz 2 (10 decks)

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