Antibiotics

Question 1

What are the characteristics of antibiotics?

Answer 1

Bactericidal - kill bacteria.

Bacteriostatic - Inhibit growth of bacteria.

Question 2

What is the mode of action of antibiotics?

Answer 2

They interfere with essential cellular structures/processes. They target bacteria-specific structures/processes. Essential cell structures include: cell wall, plasma membrane and protein synthesis.

Question 3

Explain gram positive bacteria.

Answer 3

Stain purple. Include staphylococci, streptococci, enterococci. Cell walls have thick layers of peptidoglycan

Question 4

Explain gram negative bacteria.

Answer 4

Colour pink. E.coli, pseudomonas, salmonella. Cell walls have a think peptidoglycan layer.

Question 5

What are the antibiotics that act on peptidoglycan biosynthesis?

Answer 5

Penicillins, Cephalosporins, Carbapenems, Vancomycin.

Question 6

What are B-lactam antibiotics?

Answer 6

They are effective against growing and dividing cells. Kill bacteria by autolysis. Resistant bacterial species will produce B-lactamase.

Question 7

How do B-lactam antibiotics work?

Answer 7

Inhibit the enzymes that are involved in the transpeptidase cross-linking reaction. Interfere with linking the chains together. Disrupt PG synthesis.

Question 8

Name the B-lactam antibiotics.

Answer 8

Penicillins e.g amoxicillin, Cephalosporins e.g cefalexin, Carbapenems e.g meropenem.

Question 9

What are the key characteristics of penicillins?

Answer 9

Very effective against gram +ve bacteria. Some allergy reactions. Aminopenicillins are better tolerated.

Question 10

What are the key characteristics of Cephalosporins?

Answer 10

Gram +ve, Anaerobes, Gram -ve and Pseudomonas.

Question 11

What are the key characteristics of carbapenems?

Answer 11

Broad spectrum, generally effective against all BUT: MRSA and VRE. Only available IV.

Question 12

What is Vancomycin?

Answer 12

An inhibitor of CW biosynthesis. Different mode of action to B-lactams and different chemical structure. It is a Glycopeptide abx which causes more allergic reactions. Effective against MRSA. Administered IV.

Question 13

What cell structure is involved in protein synthesis?

Answer 13

Ribosome. Bacterial ribosomes are smaller than human ribosomes.

Question 14

Which antibiotics bind to and inhibit protein components of the 30S subunit?

Answer 14

Tetracycline. Aminoglycosides e.g Gentamycin.

Question 15

Which antibiotics bind to and inhibit protein components of the 50S subunit?

Answer 15

Macrolides e.g Erythromycin. Chloramphenicol.

Question 16

What are the characteristics of abx that inhibit protein synthesis?

Answer 16

Broad spectrum - effective against both gram +ve and gram -ve species. Most are bacteriostatic. Associated with greater toxicity.

Question 17

What are the antibiotics called that inhibit DNA synthesis?

Answer 17

Fluroroquinolones e.g Ciprofloxacin, Norfloxacin, Levofloxacin etc

Question 18

What do fluoroquinolones do?

Answer 18

Broad spectrum. Inhibit bacterial enzymes with essential roles in DNA replication. Effective against Gram-ve bacteria and intracellular pathogens.

Question 19

What does Rifampicin do?

Answer 19

Inhibits bacterial but not human RNA polymerases. Used predominantly for treating TB.

Question 20

What does biosynthesis of nucleotides require?

Answer 20

Folic acid - only produced by bacteria. Folic acid synthesis is a target of man-made antibiotics.

Question 21

What are the antibiotics called that inhibit folic acid synthesis?

Answer 21

Trimethoprim, Sulphonamide, Co-trimoxazole.