Antibacterials

Question 1

What are the 4 categories of antimicrobial agents?

Answer 1

Antibacterial, antiviral, antifungal and antiprotozoal

Question 2

What is the difference between a bactericidal and bacteriostatic antibacterial agent?

Answer 2

Bactericidal - destroy bacteria

Bacteriostatic - inhibit bacterial replication

Question 3

What do we mean by “spectrum” when referring to antibacterials?

Answer 3

Antibacterials can be broad or narrow spectrum. Broad spectrum antibacterials work against multiple types of bacterial species. Narrow spectrum antibacterials may be serotype, species, genus, or gram specific

Question 4

What are the ideal features of antimicrobial agents?

Answer 4

Selective toxicity
Minimal adverse affects
Reach site of infection
Oral/IV formulation
Long half-life
No interference with other drugs

Question 5

What do the 4 classes of antibacterials target as their mechanism of action?

Answer 5

1 - cell wall synthesis (stability)
2 - protein synthesis (growth)
3 - nucleic acid synthesis (replication)
4 - cell membrane function (survival)

Question 6

Class 1 antibacterials target what bacterial function?
Give the 2 main types of class 1 antibacterial

Answer 6

Cell wall synthesis

Beta-lactams and glycopeptides

Question 7

Class 2 antibacterials target what bacterial function?
Give the 3 main types of class 2 antibacterial

Answer 7

Protein synthesis

Tetracyclines, aminoglycosides and macrolides

Question 8

Class 3 antibacterials target what bacterial function?
Give the main type of class 3 antibacterial

Answer 8

Nucleic acid synthesis

Quinolones

Question 9

Class 4 antibacterials target what bacterial function?
Give the main type of class 4 antibacterial

Answer 9

Cell membrane function

Polymixins

Question 10

What class of antibacterial and type of this class is penicillin?
How does penicillin produce its antibacterial effect?

Answer 10

Class 1 beta-lactam
Binds to penicillin binding protein inhibiting the cross-linking of cell wall peptidoglycans, causing the cell wall to destabilise and fragment

Question 11

What class of antibacterial and type of this class is vancomycin?
How does vancomycin produce its antibacterial effect?

Answer 11

Class 1 glycopeptide
Vancomycin sits on the cross-linking site sterically preventing the formation of cross-links causing the cell wall to destabilise and fragment

Question 12

What class of antibacterial and type of this class are fluoroquinolones? How do they produce its antibacterial effect?

Answer 12

Class 3 Quinolones
Interfere with DNA replication by binding to topoisomerase IV and DNA gyrase so bacterial chromosomes can’t be unraveled and transcribed

Question 13

What are the 3 main mechanisms of antibiotic resistance?

Answer 13

Drug inactivating enzymes - Beta-lactamases

Altered targets - D-lactate in vancomycin resistance, penicillin-binding protein with a lower affinity for beta-lactams in methicillin resistance

Altered drug uptake - decreased permeability (beta-lactams), increased efflux (tetracyclines)

Question 14

By what 2 general mechanisms can antibiotic resistance be obtained?

Answer 14

Chromosomal gene mutation

Horizontal gene transfer

Question 15

What are the 3 main forms of horizontal gene transfer?

What are the 3 main types of bacterial genetic information?

Answer 15

Conjugation, transduction, transformation

Chromosomes, plasmids, transposons

Question 16

What 2 methods can be used to test antibiotic activity?

Describe each briefly

Answer 16

Disc sensitivity testing - An agar plate has a bacterium containing solution spread over it then a ring of antibiotic discs are laid out upon it. The radius of the ring where colonies fail to grow indicates the efficacy of that antibiotic.

Minimum inhibitory concentration - An antibiotic is serially diluted (2ml, 1ml, 0.5ml etc) in tubes and lined up, compare tubes to a positive and negative control and last dilution before appearance of bacteria in broth indicates minimum

Question 17

What are the 4 main types of beta-lactams?

Answer 17

Penicillins
Cephalosporins
Carbapenems
Monobactams

Question 18

Describe where each of these penicillins are most effective:
Penicillin
Amoxicillin
Flucloxacillin

Answer 18

Penicillin - streptococci (most now resistant)
Amoxicillin - gram positives and some gram negatives
Flucloxacillin - staphylococci and streptococci

Question 19

Describe where each of these beta-lactamase inhibitor combinations are most effective:
Co-amoxiclav
Piperacillin

Answer 19

Co-amoxiclav - staph, strep, anaerobes and more gram negatives
Piperacillin - staph, strep, anaerobes and even more gram negatives inc. pseudomonas

Question 20

What microbes are the cephalosporins effective against?

What microbes are they not effective against?

Answer 20

Gram negatives

Anaerobes

Question 21

Which cephalosporin would be used to treat meningitis and why?

Answer 21

Cetriaxone

Good activity in CSF

Question 22

What concern is associated with cephalosporins?

Answer 22

Increased incidence of C Diff infection

Question 23

What is the most useful group of broad spectrum antibiotics? Name one of these.
What microbes are they effective against?

Answer 23

Carbapenems
Meropenem
Most gram negatives inc. anaerobes

Question 24

Carbapenems are useful for patients with what condition?

Answer 24

Penicillin allergy

Question 25

What microbes are the glycopeptides effective against? Which glycopeptide is used to treat C Diff and why? What concerns should you have when prescribing this?

Answer 25

Most gram positives Vancomycin - orally administered it is not absorbed in the GI tract Narrow therapeutic window

Question 26

Describe the antibiotic effects of tetracycline and how it is administered. Name 3 patient conditions in which you would consider tetracycline. To what patients must tetracycline not be prescribed?

Answer 26

Broad spectrum against gram positives administered orally Penicillin allergy, pneumonia caused by atypical pathogens, chlamydia Children under 12

Question 27

What is the most common aminoglycoside used? What microbes is it effective against? What concerns do we have when prescribing it? On what occasion is it generally used?

Answer 27

Gentamicin Gram negative bacteria Nephrotoxicity and ototoxicity Severe gram negative sepsis

Question 28

Name a macrolide and the bacteria it is effective against. | What positive attributes does this macrolide have?

Answer 28

Erythromycin Gram positives Well distributed inc. intracellular penetration

Question 29

What is the most commonly prescribed quinolone and what is its target? What bacteria is it effective against? What concerns do we have regarding this antibiotic?

Answer 29

Ciprofloxacin Inhibits DNA gyrase Gram negatives and atypical pathogens Increasing resistance and risk of C Diff

Question 30

``` What class of antibiotic is trimethoprim? What does trimethoprim inhibit? In what conditions is trimethoprim prescribed? ```

Answer 30

Class 3 DNA synthesis and folic acid synthesis UTIs, middle ear infections and traveller's diarrhoea

Question 31

What antibiotic is trimethoprim combined with to produce co-trimoxazole? In what conditions is it prescribed?

Answer 31

Sulfamethoxazole | Pneumocystis pneumonia in HIV, MRSA, UTIs