An Infection Model And Antimicrobials

Question 1

Name the different mechanisms of infection

Answer 1

Contiguous (direct) spread
Inoculation 
Haematogenous 
Ingestion 
Inhalation 
Vector 
Vertical transmission

Question 2

What factors affect the patient’s risk of infection?

Answer 2

Age 
Gender
Physiological state 
Genetics/epigenetics 
Pathological state/co-morbidities 
Social factors

Question 3

What are the 2 types of time in relation to infection?

Answer 3

Calendar time (time of year)
Relative time (since pt exposure)

Question 4

What is the difference between exotoxins and endotoxins?

Answer 4

Exotoxins: deliberately released by microorganisms as a virulence factor
Endotoxins: released in bacterial cell breakdown

Question 5

What are the 2 general types of treatment?

Answer 5

Specific

Supportive

Question 6

What are the different outcomes of infection?

Answer 6

Cure
Chronic infection (+/- disability)
Death

Question 7

Describe the different ways of classifying antibacterials

Answer 7

Bactericidial or Bacteriostatic
Broad vs Narrow spectrum
Target site
Chemical structure

Question 8

Describe the ideal features of antimicrobials

Answer 8

Selectively toxic 
Few adverse effects
Reaches site of infection 
Oral/IV formulation 
Long half-life 
No interference with other drugs

Question 9

What are the different target sites for antimicrobials?

Answer 9

Cell wall synthesis
Protein synthesis
Nucleic acid synthesis
Cell membrane function

Question 10

Name the classes of antimicrobials that interfere with cell wall synthesis

Answer 10

Beta lactams

Glycopeptides

Question 11

Name the classes of antimicrobials that interfere with protein synthesis

Answer 11

Tetracyclines
Aminoglycosides
Macrolides

Question 12

Name an antimicrobial class that interferes with nucleic acid synthesis and give some examples

Answer 12

Quinolones (rifampicin and trimethoprim)

Question 13

Name an antimicrobial class that interferes with cell membrane function

Answer 13

Polymyxins (colistin)

Question 14

How does penicillin work?

Answer 14

Binds to penicillin binding protein to prevent it linking parts of the cell wall together
Without it there is no rigidity of cell wall therefore the organism does not remain viable

Question 15

How does vancomycin work?

Answer 15

Active against gram positive organisms

Sits on the cross linking chains and prevents penicillin binding protein from doing its job

Question 16

How do fluoroquinolones work?

Answer 16

Inhibit 2 enzymes which deal with replication of nucleic acids
Prevents the organism from multiply
Broad spectrum Abx for gram positive and negative bacteria

Question 17

Describe the mechanisms of resistance of bacteria

Answer 17

Drug inactivating enzymes
Altered target
Altered uptake of drug (decreased permeability or increased efflux)
Genetic (mutation and horizontal gene transfer)

Question 18

Name the 3 mechanisms of horizontal gene transfer

Answer 18

Conjugation
Transduction (bacteriophages)
Transformation (directly through the cell wall)

Question 19

Define minimum inhibitory concentration

Answer 19

The lowest concentration of antibiotic that will have an inhibitory effect on the organism

Question 20

Name the 4 main classes of beta lactams

Answer 20

Penicillins
Cephalosporins
Carbopenems
Monobactams

Question 21

Penicillin is mainly activated against which organisms?

Answer 21

Mainly gram positive streptococci

Used to be staphylococci but most are resistant now

Question 22

Amoxicillins are mainly active against which organisms?

Answer 22

Gram negatives

Question 23

Flucloxacillin is active against…

Answer 23

Staphylococci and streptococci

Except MRSA

Question 24

Describe cephalosporins

Answer 24

Broad spectrum Abx but not active against anaerobes

Ceftriaxone has good activity in the CSF (therefore good for meningitis)

Question 25

Describe carbapenems

Answer 25

Very broad spectrum Active against most gram negatives Generally safe in a penicillin allergy

Question 26

Vancomycin is what type of Abx?

Answer 26

Glycopeptide

Question 27

Describe the features of vancomycin

Answer 27

Active against most gram positive Some enterococci are resistant Resistance in staphylococci is rare Narrow therapeutic window

Question 28

Describe the features of tetracyclines

Answer 28

Broad spectrum not specifically used when there is a penicillin allergy Usually for gram positives Active against atypical pathogens in pneumonia Active against chlamydia and some protozoa Shouldn't be given to children under 12 (stain teeth and bones)

Question 29

Describe the features of aminoglycosides

Answer 29

``` Eg. Gentamicin Profoundly active against gram negatives Good activity in the blood and urine Potentially nephrotoxic Narrow therapeutic window Reserved for severe gram negative sepsis ```

Question 30

Describe the features of macrolides

Answer 30

Eg. Erythromycin Alternative to penicillin for mild gram positive infections Active against atypical respiratory pathogens

Question 31

Describe the features of quinolones

Answer 31

``` Eg. Ciprofloxacin Inhibit DNA gyrase Very active against gram negatives Active against atypical pathogens Increasing resistance and risk of Clostridium difficile ```

Question 32

What is the mechanism of trimethoprim?

Answer 32

Inhibitor of folic acid synthesis

Question 33

Describe azoles (antifungals)

Answer 33

Active against yeasts and moulds | Inhibit cell membrane synthesis

Question 34

Describe polyenes (antifungals)

Answer 34

Inhibit cell membrane function Topical treatment of candida Can get some for IV treatment of systemic fungal infections

Question 35

Describe aciclovir (antiviral)

Answer 35

Inhibits viral DNA replication | Active against herpes simplex and varicella zoster

Question 36

How does Tamiflu work? (Oseltamivir)

Answer 36

Inhibits viral neuraminidase | Used for influenza A and B

Question 37

What is metronidazole?

Answer 37

An antibacterial and anti protozoal against

Question 38

Describe the features of cellulitis

Answer 38

Often caused by strep pyogenes Spread through superficial dermis Enzymatically breaks down the CT of the dermis - allowing the organism to spread Swollen, hot, red, painful

Question 39

Describe the features of necrotising fasciitis

Answer 39

Mixed synergistic bacterial infections 'Flesh-eating' Death of the body's soft tissue Red/purple skin, severe pain, fever and vomiting Most common areas = limbs and perineum Typically enters through a break in the skin eg. Cut or burn