Antimicrobials

Question 1

What can antimicrobial agents be classified as?

Answer 1

Bactericidal or bacteriostatic
Spectrum (narrow or broad)
Target site (mechanism of action)
Chemical structure (antibacterial class)

Question 2

What are the ideal features of antimicrobial agents?

Answer 2

selectively toxic
Few adverse affects
Reactivate of infection 
Oral/IV formulation
Long 1/2 life (infrequent doses) 
no interference with other drugs

Question 3

What antimicrobials affect cell wall synthesis?

Answer 3

Beta lactams and glycopeptides

Question 4

what antimicrobials affect cell membrane function?

Answer 4

Polymixins e.g. colistin

Question 5

What antimicrobial s affect protein synthesis?

Answer 5

Tetracylines
Aminoglycosides
Macrolides

Question 6

What antimicrobials affect nucleic acid synthesis?

Answer 6

Quinolones

Question 7

What is penicillins mechanism of action?

Answer 7

BETA-LACTAM Binds to protein and prevents the pencillin binding protein binding and making crosslinks and therefore inhibiting the transpeptidase that catalyzes the final step in cell wall biosynthesis.

Question 8

What is the mechanism of action of Fluoroquinolones?

Answer 8

Binds to two nuclear enzymes inhibiting
DNA replication:
Topoisomerase IV and DNA gyrase

Question 9

Discuss the mechanism of resistance of antimicrobial’s?

Answer 9

Drug inactivating enzymes e.g. B-lactamase, aminoglycoside enzymes
Altered target: target enzyme has lowered affinity for antibacterial e.g. resitance to meticllin, macrolides and trimethoprim
Altered uptake; decrease in permeability (B-Lactams) or increase in efflux (e.g. tetracyclines)

Question 10

What are the genetic basis for abx resistance?

Answer 10

Chromosomal gene mutation

Horizontal gene transfer

Question 11

What is conjugation in relation to horizontal gene transmission?

Answer 11

Process involves the transfer of DNA via a plamsid from a donor cell to a recombinant recipeient cell during cell to cell contact

Question 12

What is transduction (HGT)?

Answer 12

process by which bacterial DNA is moved from one bacterium to another by a virus

Question 13

What is transformation (HGT)?

Answer 13

genetic alteration of a cell resulting from the introduction uptake and expression of foreign genetic material

Question 14

How do we measure antibiotic activity?

Answer 14

Disc testing (zone of inhibition surrounding disc if abx works) 
minimu inhibitory concentration: the lowest conc. oif a chemical that prevents visible growth of a bacterium

Question 15

What are B-lactams? Give examples

Answer 15

A class of BROAD spectrum abx, contain a B-lactam ring.
Penicillin derivatives
Cephalosporins 
Carbopenems 
Monobactams

Question 16

Discuss Penicillin’s and their uses.

Answer 16

Penicillin- mainly active against streptococci
Amoxicillin- also some activity against gram negatives
Flucloxacillin- active against staphlococci and streptococci
B-lactamase inhibitor combination:
- Co-amoxiclav (all of the above –> Aneroboes + increased gram neg)
- piperacillin/tazobactam (as above + increaed gram neg including pseudomonas)

Question 17

Discuss cephalosporons and their uses.

Answer 17

Generations with increased Gram neg and decreased gram pos
Broad spectrum, but no anaerobe activity
Cetriaxone has good activity in the CSF: Neisseria meningitidis (and therefore also n.gonorrhea)
concern over C.diff

Question 18

Discuss Carbopenems and their uses.

Answer 18

(meropenem)
Very broad spectrum (incl. anaerobes)
active against most (not all) gram negs
Generally safe in penicillin allergy other than anaphylaxis

Question 19

Discuss Vancomycin and its uses

Answer 19

Glycopeptide (cell wall synthesis)
active against most gram +ve (not gram -ve)
Some enterococci resistant (VRE)
Resistance in staph is rare
Not absorbed (oral for C.diff ONLY)
Therapeutic drug monitoring required- Narrow Therapy Window

Question 20

Discuss Teicoplain and its uses

Answer 20

Glycopeptide (cell wall synthesis)
Similar activity to Vancomycin
Easier to administer

Question 21

Discuss Tetracylines and doxycycline and their uses.

Answer 21

Tetracylclines (protein synthesis)
Similar spectrum but ORAL only
Broad spectrum but specific use in penicillin allergy
usually for gram +ve
Active in atypical pathogens in pneumonia
Active against chlamydia & some protozoa
Shoudlnt be given to children under 12

Question 22

Aminoglycosides and their uses

Answer 22

Most common agent is gentomicin 
profound activity agfainst gram -ve 
Good activity in the blood/urine
Potentially nephrotoxic/ototoxic
Therapeutic drug monitoring required 
Generally resevred for severe gram neg sepsis

Question 23

Macrolides uses

Answer 23

e.g. erythromycin
Well distributed including intracellular penetration
Alternative to penicillin for mild gram positive infections
also active against atypical respiratory pathogens