SESIÓN 08 ANTIBIÓTICOS

Question 1

What is bactericidal activity? And what is theminimum bactericidalconcentration (MBC)?

Answer 1

• Level ofantimicrobial activity that kills the test organism. MBC is the the lowest concentration that kills 99.9% of the population.

Question 2

What is antibiotic antagonism?

Answer 2

• Combination of anitibiotics in which the activity of one antibiotic interferes with the activity of the other one.

Question 3

What is B-lactamase?

Answer 3

• An enzyme that hydrolyzes the B-lactam ring in the B-lactam class of antibiotics, thus inactivating the antibiotic.

Question 4

What 4 actions can an antibiotic have?

Answer 4

Disruption of cell wall, Inhibition of protein synthesis, inhibition of nucleic acid synthesis, and antimetabolite.

Question 5

Name the antibiotics that disrupt cell wall. (14)

Answer 5

-Penicillins, cephalosporins, cephamycins, carbapenems, monobactams.

B-lactam/B-lactamasa inhibitors

Vancomycin

Daptomycin

Bacitracin

Polymyxins

Isoniazid
Ethionamide

Ethambutol

Cycloserine

Question 6

Name the antibiotics that inhibit protein synthesis. (8)

Answer 6

• Aminoglycosides

Tetracylines

Glycylcyclines

Oxazolidinone

Macrolides
Ketolides
Clindamycin
Streptogramins

Question 7

Name the antibiotics that inhibit nucleic acid synthesis. (4)

Answer 7

• Quinolones

Rifampin
Rifabutin

Metronidazole

Question 8

Name the antibiotics that are antimetabolites. (3)

Answer 8

Sulfonamides

Dapsone

Trimethoprim

Question 9

Which antibiotics have the action that Bind PBPs and enzymes responsible for peptidoglycan synthesis? (5)

Answer 9

• Penicillins, cephalosporins, cephamycins, carbapenems, monobactams.

Question 10

Which antibiotics have the action that Binds B-lactamases and prevents enzymatic inactivation of B-lactam.

Answer 10

• B-lactam/B-lactamasa inhibitors

Question 11

What does vancomycin do especifically and to what type of bacteria is ineffective and why?

Answer 11

• Inhibits the cross-linkage of peptidoglycan layers by interaction with the D-alanine-D-alanine termini of the pentapeptide side chains. It is ineffectiva against G(-) bacteria because the molecule is too large to pass thru the outer membrane pores and reach the peptidoglycan target sites.

Question 12

What does daptomycin do especifically and to what type of bacteria is ineffective and why?

Answer 12

• Causes depolarization of cytoplasmic membrane, resulting in disruption of ionic conc. gradients. Ineffective againts G(-) because it can’t penetrate thru the cell wall to the cytoplasmic membrane.

Question 13

What does bacitracin do especifically, how is it used and to what type of bacteria is ineffective and why?

Answer 13

• Inhibits bacterial cytoplasmic membrane and movement of peptidoglycan precursors. Used topically to treat skin inffections, ineffective against G(-) b/c it can’t penetrate to the cell wall.

Question 14

What does polymyxins do especifically, how is it used and to what type of bacteria is ineffective and why?

Answer 14

• Inhibit bacterial membranes by acting interacting with the outer membrane, increasing cell permeability and eventual death. Used in localized infections b/c they can cause nephrtoxicity. Useful againts G(-) rods b/c G(+) do not have an outer membrane.

Question 15

What are Isoniazid, Ethionamide, Ethambutol, and Cycloserine used for?

Answer 15

• Treatment of mycobaterial infections.

Question 16

What do Isoniazid and ethionamide do specifically?

Answer 16

• Inhibit mycolic acid synthesis.

Question 17

What does ethambutol do specifically?

Answer 17

• Inhibit arabinogalactan synthesis

Question 18

What does cycloserine do specifically?

Answer 18

• Inhibits cross-linkage of peptidoglycan layers

Question 19

What do aminoglycosides do specifically and on what type of bacteria are they used?

Answer 19

• Produce premature release of aberrant peptides chains from 30s ribosomes. Used on G (-) rods.

Question 20

What do tetracyclines do specifically and on what type of bacteria are they used?

Answer 20

• Prevent polypeptide elongation at 30s ribosomes. Used both G(-) and G (+). It a broadspectrum bacteriostatic antibiotics.

Question 21

What do glycylcyclines do specifically and on what type of bacteria are they used?

Answer 21

• Bind to 30S ribosome and prevent initiation of protein synthesis. Used both G(-) and G (+).

Question 22

What do oxazolidinones do specifically?

Answer 22

• Prevents initiation of protein synthesis at 50S ribosomes.

Question 23

What antibiotics prevent polypeptide elongation at 50S ribosomes? (4)

Answer 23

• Macroglides, Ketolides, Clindamycin, Streptogramins

Question 24

What do Quinolones do specifically and on what type of bacteria are they used?

Answer 24

• Bind to alfa subunit of DNA gyrase. Used both G(-) and G (+).

Question 25

What do Rifampin and Rifabutin do specifically and on what type of bacteria are they used?

Answer 25

• Prevent transcription by binding DNA-dependent RNA polymerase. Used on G (+) because G (-) are intrinsically resistant to it.

Question 26

What does metronidazole do?

)

Answer 26

• Disrupts bacteria DNA (is cytotoxic compound

Question 27

What do sulfonamides do specifically?

Answer 27

• Inhibit dihydropteroate synthase and disrupts folic acid synthesis

Question 28

What does Dapsone do specifically?

Answer 28

• Inhibit dihydropteroate synthase

Question 29

What does Trimethoprim do specifically?

Answer 29

• Inhibit dihydrofolate reductase and disrupts folic acid synthesis.