Antimicrobials

Question 1

What is bacteriostatic vs bactericidal?

Answer 1

Cidal kills

Static prevents reproduction

Question 2

What is broad vs narrow spectrum antibiotic

Answer 2

Broad - gram pos and neg

Narrow - specific families

Question 3

What are 3 common target areas in the cell for antibiotics?

Answer 3

Cell wall
Protein synthesis
Nucleic acid synthesis

Question 4

What are 6 ideal features of antimicrobial agents?

Answer 4

Selectively toxic (i.e. not to host cells)
Few adverse affects
Reach site of infection
IV/Oral
Long half life (infrequent dosing)
No interference with other drugs

Question 5

How does penicillin work?

beta lactam

Answer 5

Inhibits cell wall synthesis of the bacteria by preventing the cross-linking of side chains

Question 6

How does vancomycin work?(beta lactam)

Answer 6

Similar to penicillin prevents linking of side chains and preventing synthesis of cell wall of bacteria

Question 7

How do fluoroquionolones work?

e.g. ciprofloxacin

Answer 7

By inhibiting DNA gyrase/Topoisomerase - DNA synthesis

Question 8

How does trimethoprim work?

Answer 8

By preventing folic acid synthesis and therefore preventing DNA synthesis

Question 9

What is the basis behind antibiotics that prevent protein synthesis?

Answer 9

All work on bacterial 70s ribosomal unit and inhibit function. e.g. tetracyclins Gentamycin

Question 10

How do bacteria develop resistance to beta lactams?

Answer 10

Synthesis beta lactamase enzyme that attacks the beta lactam ring

Question 11

What 3 types of microbial resistance is there?

Answer 11

Intrinsic - never been a target for that bacteria so has no effect - permanent
Acquired - e.g. mutated - usually permanent
Adaptive - responds to a stress e.g. sub inhibitory level of antibiotic - usually reversible

Question 12

Name 3 mechanisms of antibiotic resistance

Answer 12

Drug inactivating enzyme - beta lactamase

Altered uptake
E.g. antibiotics that normally get through porins in cell wall may have reduced permeability - e.g. beta lactams
or increased efflux - e.g. tetracyclines (cell has mechanism to push antibiotic out)

Question 13

How does methicillin become resistance?

Answer 13

Target enzyme has reduced affinity

Question 14

Why is it useful to know resistance of antibiotics (2)?

Answer 14

To help choose right antibiotic

To know risks of antibs that are developing resistance to them

Question 15

What is transposon?

Answer 15

A small free bit of DNA in a bacteria, that can incorporate into plasmids/bacteriophages

Question 16

What is a plasmid?

Answer 16

A plasmid is a small DNA molecule within a cell that is physically separated from a chromosomal DNA and can replicate independently.

Question 17

What is conjugation, transduction and transformation?

Answer 17

Three methods of horizontal gene transfer that can lead to antibiotic resistance in bacteria

Conjugation –> genes passed during cell reproduction

Transduction –> transduced into another bacterial cell via a bacteriophage

Transformation –> free DNA enters recipient through pores

Question 18

Does horizontal gene transfer happen just within one bacterial species?

Answer 18

No can go from one species to another

Question 19

What is the genetic basis for antibiotic resistance (2)?

Answer 19

1) Chromosomal mutation

2) Horizontal transfer:
Conjugation
Transduction
Transformation

Question 20

How does chromosomal mutation occur?

Answer 20

Chance mutation that is resistant - survives - multiplies

Question 21

How do you measure antibiotic sensitivity of bacteria?

Answer 21

Disc test - put antiB around bacteria and watch to see the prevention of bacterial growth on the plate

Question 22

What is the minimum inhibitory concentration?

Answer 22

Minimum concentration of antibiotic that prevents growth of the organism. Doubling of concentration each time until growth of bacteria stops

Question 23

What is the most broad spectrum antibiotic?

Answer 23

Meropenem

Question 24

What are penicillins mainly active against?

Answer 24

Streps

E.g strep pneumoniae, strep pyogenes, strep viridans

Question 25

Which of the penicillins also has some activity against gram negs? Give an example of a disease where you would use this?

Answer 25

Amoxicillin
Haemophillus influenza
Pneumonia

Question 26

When would you use flucloxacillin? Give an example

Answer 26

If resistant to penicillin - staph aureus

E.g. cellulitis from staph aureus

Question 27

Which antibiotic has good CSF activity? Is it gram+ neg or both? What is a concern with it?

Answer 27

Ceftriaxone –> meningitis

Both

C diff

Question 28

What is aerotolerant vs facultative anaerobe?

Answer 28

Aerotolerant is anaerobic but can tolerate O2

Facultative anaerobe is preference for O2 but can tolerate no O2

Question 29

Which two of the major organisms from lectures are mostly anaerobic?

Answer 29

Strep pyogenes (aerotolerant)
Clostridium difficile - anaerobic

Question 30

Which are aerobic (4)?

Answer 30

Staph epidermis
Neisseria Meningitidis
Legionella Pneumophillia
Salmonella Typhi

Question 31

Which are facultatively anaerobic (5)

Answer 31

Staph aureus
Strep pneumoniae 
Strep viridans
Haemophillus influenzae
E.Coli

Question 32

What bacteria is trimethoprim good against?

Answer 32

E.Coli

Question 33

When would you use Acyclovir? How does it work?

Answer 33

Viruses
e.g.
Herpes simplex virus
Varicella Zoster virus - chicken pox/shingles
When phosphorylated it inhibits viral DNA polymerase

Question 34

When would you use fluconazole? How does it work?

Answer 34

To treat fungal –> thrush candida. Inhibits cell membrane synthesis