Microbiology Antibiotic Summary

Question 1

What does selectively toxic mean?

Answer 1

Antibiotic must kill bacteria without killing host

Question 2

Bactericidal?

Answer 2

Kills bacteria

Question 3

Bacteriostatic?

Answer 3

Inhibits bacterial growth

Question 4

How can antibiotics work? What can they act on?

Answer 4

Bacterial cell walls (mammalian cells dont have a cell wall)
Affecting the bacterial ribosome (mammalian ribosomes are structurally different)
Acting on bacterial DNA directly (Bacterial DNA is structurally different from mammalian DNA - bacteria have a single circular chromosome)

Question 5

What are the antibiotics that act on the cell wall?

Answer 5

Penicillins
Cephalosporins
Glycopeptides

Question 6

Describe Penicillin?

Answer 6

Inhibits cell wall synthesis
It's bactericidal 
Safe, few side effects
Narrow/borad spec
Excreted rapidly via kidneys

Question 7

Describe Cephalosporins?

Answer 7

Inhibit cell wall synthesis by preventing the cross linking of peptidoglycan
Bactericidal
Excreted in kidneys and urine
Broad spec - Affects normal bowel flora - leading to C.DIFF - avoided due to this

Question 8

Describe glycopeptides?

Answer 8

Bind to the growing end of the pentapeptide chain during peptidoglycan synthesis preventing cross linking and weakening bacterial cell wall
Bactericidal
Excreted via kidneys and urine (be careful in patients with kidney failure)
Only active against GRAM POSITIVE
Must be given IV

Question 9

What are the 3 forms of penicillin available?

Answer 9

Benzylpenicillin
Phenoxymethyl penicillin
Long acting penicillin

Question 10

Describe flucoxacillin?

Answer 10

Given IV or oral
Gram positive only - strep and staph (narrow spec)
used for: wound/skin infections etc

Question 11

Describe amoxicillin

Answer 11

beta lactase destroys amoxicillin
Commonly used
Gram negative and positive
Given IV and oral

Question 12

Co-amoxiclav?

Answer 12

Mix between amoxicillin and Clavulanic acid

Makes it resistant to beta lactamase

Question 13

Describe temocillin?

Answer 13

IV only

only active against coliforms

Question 14

Describe pipercillin/tazobactam?

Answer 14

resistant against b-lactamase
broad spec
wont treat MRSA
resistant to colifoms?

Question 15

How do antibiotics that inhibit protein synthesis usually work?

Answer 15

They do so by attaching to bacterial ribosomes which are structurally different from mammalian ribosomes.

Question 16

Describe the macrolides?

Answer 16

Erythromycin, clarythromycin and azithromycin
They are excreted via liver, binary tract and into gut - not excreted in urine
They are lipophilic - pass through cell membranes easily

Question 17

What are the antibiotics that inhibit protein synthesis?

Answer 17

Macrocodes
Aminoglycosides

(Clindamycin, Chloramphenicol, Tetracylcines)

Question 18

Describe Aminoglycosides?

Answer 18

Gentamicin (IV only)
Bacteriacidal
Mainly gram negative - coliform and pseudomonas
Excreted in urine