Antimicrobial Chemotherapy 1

Question 1

Describe what is meant by MIC.

Answer 1

Minimal inhibitory concentration.
= the concentration of antimicrobial needed to inhibit growth of bacteria.

Question 2

Describe what is meant by MBC.

Answer 2

Minimal bactericidal concentration.
= The minimum concentration of microbial required to kill a given organism.

Question 3

Describe what is meant by sensitive bacteria.

Answer 3

Sensitive bacteria are inhibited or killed by antimicrobial available at site of infection.

Question 4

Describe what is meant by resistant bacteria.

Answer 4

Resistant bacteria are not killed or inhibited by antimicrobial at site of infection.

Question 5

Describe what is meant by bactericidal antimicrobials.

Answer 5

Bactericidal antimicrobials kill bacteria.

Question 6

Describe what is meant by bacteriostatic antimicrobial.

Answer 6

Bacteriostatic antimicrobials inhibit bacteria.

Question 7

Describe what is meant by synergy.

Answer 7

Antimicrobial synergy is where two agents exert greater activity when added together.

Question 8

Describe what is meant by antagonism (in antimicrobials)

Answer 8

This is when the exertion from the combination of two agents is lesser than expected from the addition.

Question 9

State the 3 different mechanisms of action of antibiotics.

Answer 9

Inhibition of cell wall synthesis.
Inhibition of protein synthesis.
Inhibition of nucleic acid synthesis.

Question 10

Describe the process of inhibition of cell wall synthesis in Beta-Lactams (Penicillin).

Answer 10

Beta-Lactams are effective mostly against Gram-positive bacteria.
For the cell wall to be synthesised (in tact), the proteins of the cell walls need to be cross-linked.
So, Penicillin inhibits peptidoglycan synthesis by inhibiting enzymes (penicillin binding protein) responsible for cross linking the carbohydrate chains.

Question 11

Describe Beta-Lactams.

Answer 11

Beta-Lactams are antimicrobials that inhibit cell wall synthesis.
They posses a Beta-Lactam ring within their structure.

Question 12

Describe the process of inhibition of cell wall synthesis by glycopeptides.

Answer 12

Act on cell wall a stage prior to Beta-Lactams.
They inhibit the assembly of peptidoglycan precursor.
The PBP is taken up by glycopeptides.

Question 13

Describe glycopeptides.

Answer 13

Glycopeptides are bactericidal antibiotics and their inability to penetrate the gram-negative cell wall means they only act on gram-negative organisms.
e.g. Vancomycin, Teicoplanin

Question 14

Describe the process of inhibition of protein synthesis by aminoglycosides.

Answer 14

The binding of aminoglycosides to the 30s subunit of the ribosome, impairs translational proof reading leading to misreading of RNA message premature termination and inaccuracy of the translated protein.

Question 15

Describe aminoglycosides.

Answer 15

Concentration dependent bactericidal antibiotics.
Useful in treatment of serious gram negative infection (e.g. gentamycin)

Question 16

Describe the process of inhibition of protein synthesis by macrolides and tetracyclines.

Answer 16

Macrolides inhibit the bacterial protein biosynthesis, by preventing peptidyltransferase from adding the growing peptide attached to tRNA to the next amino acid as well as inhibiting ribosomal translation.

Question 17

Describe a macrolide.

Answer 17

Macrolides depend on concentration and bacterial species.
These are bactericidal and bacteriostatic.
(e.g. erythromycin, clarithromycin)

Question 18

Describe the process of inhibition of protein synthesis by oxazolidinones.

Answer 18

They prevent two subunits (of the ribosome) from meeting, stopping protein synthesis.

Question 19

Describe tetracyclines.

Answer 19

Tetracyclines are bacteriostatic antibiotics.
Used for treatment of Gram positive infections.
Bacteria have become increasingly resistant.

Question 20

Describe oxazolidinones.

Answer 20

Bacteriostatic and bactericidal treatment of gram positives.
(e.g. linezolid, used for serious MRSA infection, given orally)

Question 21

Describe cyclic lipopeptides.

Answer 21

These are strong bactericidal antibiotics used for treatment of gram positive bacteria.
e.g. daptomycin

Question 22

Describe the process of inhibition of protein synthesis by daptomycin.

Answer 22

Aggregation of daptomycin alters the curvature of the membrane, creating holes.
This leaks ions out of the cell, causing rapid depolarisation = loss of membrane potential.
= inhibition of protein, DNA, RNA synthesis.
= CELL DEATH>

Question 23

Describe, generally the inhibitors of nucleic acid synthesis (purine synthesis)

Answer 23

Inhibition of DNA synthesis either directly or indirectly by interrupting the supply of precursors for DNA synthesis.
Bacteriostatic, when combined Bactericidal.

Question 24

Name some examples of inhibitors of nucleic acid synthesis (purine synthesis stage).

Answer 24

Trimethoprim (UTIs or chest infections)
Sulphamethoxazole (when combined cotrimoxazole).

Question 25

Describe fluoroquinolones.

Answer 25

These are bactericidal.
They are effective against gram-negative organisms.
They inhibit DNA synthesis by working on DNA gyrase.
(e.g. ciprofloxacin, levofloxacin).

Question 26

Name some examples of fluoroquinolones.

Answer 26

Ciprofloxacin
Levofloxacin