Antimicrobial Agents

Question 1

Antibiotics

Answer 1

selectively toxic for bacteria

Question 2

Bactericidal

Answer 2

killing

Question 3

Bacteriostatic

Answer 3

growth inhibition

Question 4

Combination therapy

Answer 4

• prevent emergence of resistant strains

- temporary treatment until diagnosis is made

Question 5

Antibiotic synergism

Answer 5

better in combination

-penicillins and amino-glycosides

Question 6

Antibiotic antagonism

Answer 6

deadly together

-penicillins and bacteriostatic antibiotics

Question 7

Antibiotic activity

Answer 7

• Inhibition of cell wall synthesis
• Inhibition of protein synthesis
• inhibition of nucleic acid synthesis RNA DNA

Question 8

B-lactam antibodies

Answer 8

B-lactams bind to the PBPs which inhibit the peptidoglycan cross linking (degrade cell wall)
ex.penicillins, cephalosporins, cephamycins, carbapenems

Question 9

Glycopeptides

Answer 9

also disrupt peptidoglycan synthesis ex. vancomycin gram positive only

Question 10

Polypeptides

Answer 10

ex. bacitracin, used topically for skin infections, interferes with dephosporylation and recycling by lipid carrier used to move peptidoglycan precursors to cell wall

Question 11

Polymyxins

Answer 11

external treatment for localized infections eye, ear, skin

• can cause kidney damage
• insert to bacterial membrane, increase cell permeability
• gram negative

Question 12

Lactam antibiotics

Answer 12

inactive against gram negative, no penetration of outer membrane

Question 13

B-lactam resistance mechanisms

Answer 13

• produce penicillinase, destroys antibiotic
• modified penicillin binding proteins, dont bind to the antibiotic
• modified porins, no internalization of antibiotic

Question 14

Clavulinic acid

Answer 14

binds strongly to B-lactamases and inhibit their activity

Question 15

Treatment for mycobacterial infections

Answer 15

• Isoniazid and ethionamide, block mycolic acid synthesis
• ethambutol, blocks arabinogalactan synthesis
• cycloserine, blocks 2 enzymes that catalyze cell wall synthesis

Question 16

Protein synthesis inhibitors

Answer 16

Mostly bacteriostatic

-selectivity due to differences in proka and euka

Question 17

Aminoglycosides

Answer 17

-amikacin, gentamicin, tobramycin, bind to the 30s ribosomal subunit induces misreading of mRNA, premature release of ribosome

Question 18

Tetracyclines

Answer 18

tetracycline, doxyxycline, minocycline
-bind to 30s ribosomal subunits block aminoacyl-tRNA binding to 30s-mRNA complex
resistance is common

Question 19

Oxazolidinones

Answer 19

linezolid

• binds to 50s ribosomal subunits distorts tRNA binding site
• interferes wth the formation of 70s initiation complex
• used for multi-drug resistant enterococci

Question 20

Also bind to 50s ribosomal subunit

Answer 20

• chloramphenicol
• macrolides
• clidamycin

Question 21

Inhibition of nucleic acid synthesis (Qunolones)

Answer 21

inhibit bacterial DNA topoisomerases required for DNA replication, recombination and repair

• gram-ve type II
• gram+ve type IV

Question 22

Inhibition of nucleic acid synthesis (Rifampin and rifabutin)

Answer 22

bind to DNA dependent RNA polymerase and inhibit initiation od mRNA synthesis

Question 23

Antimicrobial drug resistance I

Answer 23

• can arise by mutation or gene transfer
• provides selective advantage
• can result from single or multiple steps

Question 24

Antimicrobial drug resistance II

Answer 24

• altered permeability, influx gram -, efflux tetracycline
• altered target site, penicillin binding proteins (penicillins), RNA polymerase (rifampin), 30S ribosome (streptomycin)
• replacement of a sensitive pathway, acquisition of a resistant enzyme