Block 2

Question 1

Disinfectants

Answer 1

Toxic to humans and bacteria (Bleach)
Nonspecific
Used to eliminate organisms on inanimate objects

Question 2

Antiseptics

Answer 2

Generally toxic to bacteria
Nonspecific effects
too toxic for systemic use in humans (e.g. peroxides, alcohol)
OK for topical use

Question 3

Antibiotics

Answer 3

Targets specific cellular processes
exhibit effects on bacteria but not humans- selective toxicity
con be administered systemically

Question 4

Bacteriostatic

Answer 4

inhibit growth of bacteria (but do not kill them) - rely on immune to eradicate

Question 5

Bactericidal

Answer 5

kill bacteria directly - important for immunocompromised patients

Question 6

Spectrum of activity

Answer 6

the collection of bacterial species that is susceptible to a given antibiotic

Narrow Spectrum: effective against a small group of bacteria (e.g. aerobic gram-positive bacteria)

Broad spectrum: effective against a wide range of bacteria (e.g. gram-positive and gram-negative bacteria)

Question 7

Minimum inhibitory concentration (MIC)

Answer 7

defines lowest concentration that inhibits growth of bacteria

Question 8

Minimum bactericidal concentration (MBC)

Answer 8

Defines lowest concentration of antibiotic that kills a defined proportion of bacterial population after a specified time (e.g. 99.9% of bacteria killed after 24 h)

Question 9

Horizontal gene transfer

Answer 9

acquisition of foreign DNA encoding resistance genes; can enable rapid emergence of multi-drug resistant strains

Question 10

3 Basic mechanisms of resistance

Answer 10

Modification (inactivation) of antibiotic molecule itself

Modification (reprograming) of antibiotic target

Reduction of antibiotic concentration/prevent access to target

Question 11

Antibiotics that target peptidoglycan synthesis

Answer 11

B-Lactams
Vancomycin
Bacitracin

Question 12

Antibiotics that target Ribosomes and protein synthesis

Answer 12

Tetracyclines
Aminoglycosides
Macrolides
Oxazolidinones

Question 13

Antibiotic that target DNA replication and repair

Answer 13

Fluoroquinolones

Question 14

Antibiotics that target key metabolic reactions

Answer 14

Trimethoprim

sulfamethoxazole

Question 15

Antibiotics that target the cell membrane

Answer 15

Polymyxin

Daptomycin

Question 16

B-Lactams

Answer 16

Block peptidoglycan crosslinking by binding PBPs and inactivating them

Structure of B-Lactam mimics the natural substrate for PBP

Resistance:
B-lactamase cleaves b-lactam ring of antibiotic, rendering it inactive

Mutations in PBPs

Question 17

Clavulanic Acid

Answer 17

B-Lactamase inhibitor

Contains a B-lactam ring
Binds to b-lactamase

Question 18

Glycopeptides (vancomycin)

Answer 18

Binds to D-ala-D-ala at the end of peptide side chain in peptidoglycan precursor, blocking PBP

Effective on Gram-Positive (but not Gram-Negative)

Used for B-lactam resistant infections

Vancomycin resistance occurs when the bacteria alters D-ala-D-ala to D-ala-D-lac; Vaconmycin is no longer able to bind

Question 19

Cycloserines

Answer 19

Inhibit peptidoglycan crosslinking

Competitive inhibitor of D-alanine:
alanine racemase
D-alanyl-D-alanine synthetase

Question 20

Bacitracin

Answer 20

peptide antibiotic - too toxic for systemic use

binds to pyrophosphate on the lipid carrier for peptidoglycan precursors and blocks its recycling

Question 21

Daptomycin

Answer 21

agent against the cells envelope

Bactericidal, narrow spectrum (gram-positive bacteria)

Question 22

Polymyxins

Answer 22

agent against the cell envelope

Bactericidalm narrow spectrum (gram-negative)

binds to LPS in outer membrane

Question 23

Tetracycline

Answer 23

Protein synthesis inhibitor: targets 30S function

Bacteriostatic, broad spectrum

binds 30S subunit and interferes with the binding of tRNA

Resistance: tetracycline efflux pumps (most common), mutations on ribosomes

Question 24

Aminoglycosides

Answer 24

Bactericidal, broad spectrum

binds irreversibly to 30S and causes misreading

useful for hard-to-kill gram-negative

do not penetrate many gram-positive

Question 25

Macrolides

Answer 25

(erythromycin, azithromycin, clarithromycin)

Bacteriostatic, Primarily active against gram-positive bacteria

Binds 50S subunit and blocks elongation of proteins

Resistance:
enzymatic methylation of ribosomal RNA

Efflux pumps