Antibiotics

Question 1

What term is used to describe killing or inhibiting the growth of a microorganism without harming host cells?

Answer 1

selective toxicity

Question 2

What is the difference between bacteriostatic vs. bactericidal?

Answer 2

bacteriostatic –> inhibit growth (no killing)

bactericidal –> killing

Question 3

When is bacteriostatic generally used?

Answer 3

when host defenses can be counted on

Question 4

When is bactericidal generally used?

Answer 4

during infection is severe or patient is immunocompromised

Question 5

Combination of two antibiotics with enhanced bactercidal activity when used together is known as what?

Answer 5

antibiotic synergism

Question 6

Combination of antibiotics in which one interferes with the activity of the other is known as what?

Answer 6

antibiotic antagonism

Question 7

Broad-spectrum antibiotics are effective against a large variety of bacteria, what are the advantages and disadvantages?

Answer 7

advantage: incr. likelihood of effectiveness against a bacterial infection of unknown etiology
disadvantage: incr. likelihood of disrupting the patients normal microbiota (but minor to more serious consequences)

Question 8

Narrow-spectrum antibiotics are effective against only a small subset of bacteria, what are the advantages and disadvantages?

Answer 8

advantage: avoids disruption of normal microbiota
disadvantage: must have specific disease causing bacteria identified to choose correct antibiotic

Question 9

True or False. Antibiotics cause resistance

Answer 9

FALSE

Question 10

What causes antibiotic resistance?

Answer 10

general mutation and/ or acquisition of genetic elements from other bacteria carrying resistance genes

Question 11

What are the three types of antibiotic resistance?

Answer 11

1) sensitive
2) intermediate
3) resistant

Question 12

What type of antibiotic resistance could be treated with a recommended dosage regimen of an antimicrobial agent?

Answer 12

sensitive

Question 13

What type of antibiotic resistance could be treated in body sites where the drug are physiologically concentrated or when a high dosage of drug can be used?

Answer 13

intermediate

Question 14

What type of antibiotic resistance is not usually inhibited by the usually achieved concentrations of the antimicrobial?

Answer 14

resistant

Question 15

When is empiric therapy used?

Answer 15

antibiotic treatment while waiting for lab results

Question 16

When is targeted therapy used?

Answer 16

once lab results have been received and bacteria have been identified

Question 17

What are some general mechanisms in which bacteria can become antibiotic resistant (5)?

Answer 17

1) breakdown of an antibiotic (hydrolysis)
2) chemical modification of an antibiotic
3) alteration of the target
4) altered permeability, decreased influx or increased efflux
5) lack of target

Question 18

What are the two types of activity used in antibiotic susceptibility testing?

Answer 18

1) bacteriostatic

2) bactericidal

Question 19

What is minimum inhibitory concentration (MIC)?

Answer 19

lowest concentration of antibiotic that inhibits growth

Question 20

What is minimum bactericidal concentration (MBC)?

Answer 20

lowest concentration of antibiotic that kills 99.9%

Question 21

How is MIC determined?

Answer 21

1) Kirby-Bauer Test (zone of inhibition seen in disk-diffusion assay)
2) E-test (strip of antibiotics with concentration gradient)

Question 22

How is MBC determined?

Answer 22

broth culture –> check for bacterial growth after overnight incubation

Question 23

What is targeted in cell wall active vs membrane active antibiotics?

Answer 23

cell wall active –> disrupts peptidoglycan synthesis

membrane active –> disrupts or interferes with membrane integrity/synthesis

Question 24

True or False. Cell wall active antibiotics are effective against resting and actively dividing bacteria

Answer 24

FALSE. only effective against actively dividing bacteria. it targets the making of PG, if the bacterium is already there, the antibiotics are not effective against it

Question 25

True of False. Membrane active antibiotics are effective against resting bacteria only

Answer 25

FALSE. they are effective against both resting AND actively dividing bacteria

Question 26

Are beta-lactams bactericidal or bacteriostatic?

Answer 26

bactericidal

Question 27

What is the mechanism of action of beta-lactams?

Answer 27

they inhibit cell wall synthesis, specifically they block the active site of transpeptidase

Question 28

Penicillin is an example of which type of antibiotics?

Answer 28

beta-lactams

Question 29

What are some ways bacteria become resistant to beta-lactams (4)?

Answer 29

1) altered transpeptidases 2) altered outer-membrane permeability 3) presence of efflux pumps 4) chemical modification of antibiotic

Question 30

When beta-lactams can no longer bind to the active site of transpeptidase, what kind of resistance have the bacteria undergo?

Answer 30

altered transpeptidases

Question 31

How does altered outer membrane permeability lead to beta-lactam resistance?

Answer 31

protein channels called porins gain mutations that can cause beta-lactams to no longer gain entrance inside the cell

Question 32

How does the presence of efflux pumps lead to beta-lactam resistance?

Answer 32

the antibiotics are pumped back out and that effectively reduces the antibiotic concentration within the cell

Question 33

What's an example of chemical modification of antibiotic that lead to its resistance?

Answer 33

the bacteria may have beta-lactamase, an enzyme that turns beta-lactams into its inactive form

Question 34

What is the mechanism of vancomycin?

Answer 34

it recognizes and binds to the 2 D-ala on the end of peptide chains thus preventing transpeptidase from interacting. cross-links can't be formed = cell death

Question 35

How can bacteria become resistant to vancomycin?

Answer 35

last D-ala residue has been replaced by a D-lactate and vancomycin can no longer bind to it. cross-links are once again successfully formed and so does cell wall

Question 36

What antibiotics interferes with dephoshorylation in cyclin of lipid carrier, bactoprenol?

Answer 36

bacitracin

Question 37

What antibiotics targets protein synthesis?

Answer 37

1) tetracyclines 2) aminoglycosides 3) macrolides

Question 38

Tetracyclines are bactericidal or bacterostatic?

Answer 38

bacterostatic

Question 39

Aminoglycosides are bactericidal or bacterostatic?

Answer 39

bactercidal

Question 40

Macrolides are bactericidal or bacterostatic?

Answer 40

bacteriostatic

Question 41

What ribosome subunit do tetracylines bind to?

Answer 41

30s

Question 42

What ribosome subunit do aminoglycosides bind to?

Answer 42

30s

Question 43

What ribosome subunit do macrolides bind to?

Answer 43

50s

Question 44

Which of the three protein synthesis inhibitors is generally used as an alternative for individuals with penicillin allergy?

Answer 44

macrolides

Question 45

Which of the three protein synthesis inhibitors is only effective against aerobic organisms because it is oxygen-dependent?

Answer 45

aminoglycosides

Question 46

Which of the three protein synthesis inhibitors is a broad spectrum antibiotics?

Answer 46

tetracyclines

Question 47

What are the three nucleic acid synthesis inhibitors?

Answer 47

1) quinolones 2) rigampin, rifabutin 3) metronidazole

Question 48

Which of the nucleic acid synthesis inhibitors are bactericidal?

Answer 48

all three are bactericidal

Question 49

Which of the nucleic acid synthesis inhibitors inhibits DNA replication, recombination and repair?

Answer 49

quinolones

Question 50

Which of the nucleic acid synthesis inhibitors binds to DNA-dependent RNA polymerase and inhibits initiation of RNA synthesis?

Answer 50

rifampin, rifabutin

Question 51

Which of the nucleic acid synthesis inhibitors gets reduced bacteria and becomes toxic that damages their DNA?

Answer 51

metronidazole

Question 52

What type of antibiotics is sulfonamides and trimethoprim?

Answer 52

antimetabolites

Question 53

What is the mode of action for sulfonamides and trimethoprim?

Answer 53

they target folate metabolism thus preventing bacteria from having the necessary material to build DNA and RNA