Anti-microbial drugs

Question 1

Criteria to characterise antibiotics

Answer 1

effect on bacteria:
- kill bacteria – bactericidal
- inhibit/arrest growth of bacteria – bacteriostatic
range of bacterial species affected:
- a large number of bacterial species - broad spectrum
- a limited number of bacterial species - narrow spectrum
- a single species – limited spectrum

Question 2

Targets of antibiotics

Answer 2

interfere with/inhibit essential cellular structures/processes
target bacteria-specific structures/processes
such modes of action make them
- toxic to bacteria only
- innocuous to humans (little or no-side effects)

Question 3

Essential cellular structures and processes in bacteria

Answer 3

cell wall, plasma membrane, protein synthesis

Question 4

Antibiotics that act on Peptidoglycan biopsynthesis

Answer 4

Penicillin, Cephalosporin, Carbapenem, Vancomycin

Question 5

B-lactam antibiotics

Answer 5

are effective against growing and dividing cells
kill bacteria by autolysis (bactericidal)
resistant bacterial species produce B-lactamase, a secreted enzyme which inactivates antibiotics by breaking down their B-lactam ring
Penicillin - natural (penicillin G) and aminopenicillin (amoxicillin, ampicillin)
Cephalosporins
Carbapenems

Question 6

Penicillins

Answer 6

very effective against grame positive bacteria
some allergic reactions
aminopenicillins better tolerated

Question 7

Cephalosporins

Answer 7

different primary coverage:
1st = grame positive bacteria
2nd = anaerobes
3rd = gram negative bacteria
4th - pseudomonas

Question 8

Meticillin

Answer 8

resistant to B-lactamase
replaced by more stable and similar penicillins:
Oxacillin, Flucloxacillin, Dicloxocillin

Question 9

Vancomycin

Answer 9

glyco-peptide antibiotic = more allergic reactions
an inhbitor of CW biosynthesis:
- different more of action to B-lactams, different chemical structure
effective against MRSA
- administered i.v

Question 10

Antibioitcs inhibiting protein synthesis

Answer 10

some bind to and inhibit protein components of the 30S sub unit:
eg. Tetracycline, Doxycycline
Aminoglycosides (Gentamycin, Streptomycin, Tobramycin)
others bind to, and inhibit protein components of the 50S sub-unit:
eg. Macrolides (Erythromycin, Clarithromycin), Chloramphenicol
- broad spectrum, effective against both gram negative and positive species
- most are bacteriostatic
- associated with greater toxicity

Question 11

Antiobiotics inhibiting DNA synthesis

Answer 11

Fluoroquinolones eg. Cirprofloxacin, Levofloxacin

• broad spectrum, synthetic
• inhibit bacterial enzymes with essential roles in DNA replication
• effective against gram negative bacteria and intra-cellular pathogens (legionella, mycoplasma)
• associated with high levels of toxicity

Question 12

Antibiotics inhibiting RNA bio-synthesis

Answer 12

RNA bio-synthesis requires DNA-dependent RNA polymerases

eg. Rifampicin
- inhibits bacterial but not human RNA polymerases
- used to treat TB

Question 13

Antibiotics inhibiting folate biosynthesis

Answer 13

eg. Sulfonamide
- analogues of PABA, act by substrate competition
Trimethoprim
- inhibits digydrofolate reductase
Co-trimoxazole
- a mixture of both, inhibits both steps of the pathway

Question 14

Sources of antibiotics

Answer 14

natural, produced by:
> fungi - penicillin, cephalosporin
> bacteria - erythromycin, rifampicin, streptomycin, tetracycline
semi-synthetic :
> ampicillin
snythetic:
> sulfonamides, trimethoprim

Question 15

Choice of antibiotic treatment depends on…

Answer 15

bacterial species
susceptibility to drug
site of infection
safety of drug
cost of therapy
patient fcators

Question 16

Antibiotic resistance

Answer 16

mutations in bacterial chromosomal genes encoding targets of common antibioitics (vertical gene transmission)
transfer between organisms of resistance genes carried by plasmids (horizontal gene transmission)
biofilm formation