*Microbiology 3 (lecture 5)

Question 1

What is the difference between bactericidal and bacteriostatic antibiotics?

Answer 1

Bactericidal = kill bacteria
Bcteriostatic = inhibit bacterial growth

Question 2

Why must antibiotics be selectively toxic?

Answer 2

In order to kill the bacteria without damaging the host

Question 3

How are antibiotics usually administered?

Answer 3

Usually orally or IV (rarely intramuscularly)

Question 4

When antibiotics are given orally, when will they reach peak serum levels?
When given IV?

Answer 4

Approx. 1 hour later

Within 15 minutes

Question 5

Where are antibiotics excreted?

Answer 5

Unchanged antibiotic = in the faeces

Absorbed antibiotic = either in the urine or via the liver, binary tract and into the faeces

Question 6

Why are antibiotics sometimes given in combination? (3)

Answer 6

To cover a broad range of possible infecting organisms
To prevent the development of resistance e.g. in the treatment of TB
For the synergistic effect of the combination (i.e. 1 + 1 = 3) e.g. in the treatment of some cases of endocarditis

Question 7

What are the 3 main ways in which antibiotics can work?

Answer 7

Acting on bacterial cell wall
Affecting the bacterial ribosome
Acting on bacterial DNA directly
(all of these structures differ in bacteria and mammalian cells)

Question 8

What are the 3 groups of antibiotics that act on the bacterial cell wall?

Answer 8

The penicillins
The cephalosporins
The glycopeptides

Question 9

Name the 6 penicillins?

Answer 9

Penicillin
Flucloxacillin
Amoxicillin
Temocillin
Co-amoxiclav
Piperacillin/ tazobactam = Tazocin

Question 10

Name a cephalosporin?

Answer 10

Ceftriaxone

Question 11

Name 2 glycopeptides?

Answer 11

Vancomycin

Teicoplanin

Question 12

How do the penicillins work?

Answer 12

They inhibit cell wall synthesis by preventing the cross-linking of peptidoglycan subunits

Question 13

Are the penicillins bactericidal or bacteriostatic?

Answer 13

Bactericidial

Question 14

Amount of side effects of penicillins?
Narrow or broad spectrum?
Excreted by?

Answer 14

Very few
Range from narrow to broad spectrum
Rapidly via the kidneys

Question 15

Are the penicillins safe in pregnancy?

Answer 15

Yes

Question 16

What are the 2 main drawbacks of the penicillins?

Answer 16

• some patients are hypersensitive to the penicillins. An allergy to one penicillin means allergy to all penicillins (and sometimes also the cephalosporins)
• rapid excretion via the kidney means frequent dosing (usually 4-6 times daily) is necessary

Question 17

What are the 3 forms of penicillin available? How is each given?

Answer 17

Benzylpenicillin (penicillin G, IV)
Phenoxymethyl penicillin (penicillin V, oral)
Benzathine penicillin (long actin, IM)

Question 18

Do organisms that are sensitive to penicillin itself tend to be sensitive to most of the penicillin group of antibiotics?

Answer 18

Yes

Question 19

What does the penicillin nucleus look like?

Answer 19

A house and a garage

Question 20

What penicillin is given to gram positive organisms? How can this be given?

Answer 20

Flucloxacillin (IV, oral)

Question 21

What penicillins are given to both gram positive and gram negative organisms? How re these given?

Answer 21

Amoxicillin (IV, oral)
Co-amoxiclav (IV, oral)
“Tazocin” - IV only (piperacillin/ tazobactam)

Question 22

What penicillin is given to gram negative organisms?

Answer 22

Temocillin (IV only)

Question 23

How is flucloxacillin given?

Answer 23

IV and oral

Question 24

Spectrum of flucloaxicillin?

Answer 24

Very narrow

Useful only for staphylococci and streptococci)

Question 25

What is flucloxacillin used to treat?

Answer 25

Staphylococci and streptococci infections only e.g. Skin and soft tissue infection Wound infection Cellulitis

Question 26

How can amoxicillin be given?

Answer 26

IV, oral

Question 27

Why has amoxicillin become less effective over the years?

Answer 27

Many organisms produce beta-lactamse (an enzyme that destroys amoxicillin)

Question 28

What is co-amoxiclav? | When is it used?

Answer 28

Amoxicillin plus clavulanic acid which is a beta-lactadase inhibitor Used when there is an antibiotic resistance to amoxicillin

Question 29

How can co-amoxiclav be given?

Answer 29

oral and IV

Question 30

What is tazocin made up of?

Answer 30

Piperacillin (antibiotic) | Tazobactam (beta-lactamase inhibitor)

Question 31

How is tazocin given?

Answer 31

IV only

Question 32

How is temocillin given?

Answer 32

IV only

Question 33

What type of bacteria can temocillin be used to treat?

Answer 33

Colifroms

Question 34

Can temocillin be used to treat beta-lactamase producing bacteria?

Answer 34

Yes, it is used to treat extended spectrum beta-lactamase producing organisms

Question 35

What do all cephalosporins have in their name?

Answer 35

"ceph" or "cef"

Question 36

How do cephalosporins work? | Bactericidal or bacteriostatic?

Answer 36

inhibit cell wall synthesis and are bactericidal (like penicillins)

Question 37

How are cephalosporins excreted? Few or many side effects? Safe in pregnancy?

Answer 37

Excreted via kidneys and urine Few side effects Safe in pregnancy

Question 38

Appearance of a cephalosporin nucleus?

Answer 38

House + garage + garden

Question 39

Do cephalosporins have a broad or narrow spectrum?

Answer 39

Broad-spectrum

Question 40

What is the major disadvantage of cephalosporins?

Answer 40

As they are broad spectrum, they significantly affect the normal bowel flora They kill the normal gut bacteria allowing overgrowth of clostridium difficile which causes a nasty gastroenteritis Many hospitals now try to avoid using them meaning they have very limited indications for use in Tayside

Question 41

How are the glycopeptides (vancomycin and teicoplanin) given?

Answer 41

Both IV

Question 42

How does vancomycin work? | Are the glycopeptides bactericidal or bacteriostatic?

Answer 42

Cell-wall active antibiotics but in a slightly different way to the penicillins and cephalosporins Binds to the end of the growing pentapeptide chain during peptidoglycan synthesis preventing cross-linking and weakening the bacterial cell wall Bactericidal

Question 43

How are the glycopeptides excreted?

Answer 43

Via the kidneys and urine

Question 44

What can happen to patients taking vancomycin with kidney failure?

Answer 44

Toxic levels can build up in the blood causing further kidney damage

Question 45

What type of organisms are glycoproteins active against?

Answer 45

Only gram positive cell walls - active against all (most?) gram positive bacteria

Question 46

What antibiotic can treat MRSA?

Answer 46

Vancomycin (if becomes resistant to this, we would have very few options to treat it) Gentamicin

Question 47

Antibiotics that inhibit protein synthesis? (5)

Answer 47

The macrolides The tetracyclines The aminoglycosides Others (Clindamycin, chlorampheicol)

Question 48

What are 3 macrolides?

Answer 48

Erythromycin Clarythromycin Azinthromycin

Question 49

What is an example of a teracycline?

Answer 49

Doxycycline

Question 50

What is an example of an aminoglycoside?

Answer 50

Gentamicin

Question 51

How do antibiotics inhibit protein synthesis?

Answer 51

By attaching to bacterial ribosomes (structurally different from mammalian ribosomes)

Question 52

Are antibiotics that inhibit protein synthesis (act on ribosomes) bactericidal or bacteriostatic? Why? What is the exception to this?

Answer 52

Bacteriostatic Usually protein synthesis can resume when the antibiotic is removed The amino glycoside group - binding of these antibiotics to ribosome are lethal

Question 53

How are the macrocodes excreted?

Answer 53

Via the liver, biliary tract and into the gut

Question 54

Is Erythromycin safe in pregnancy?

Answer 54

Yes

Question 55

What type of infections are macrolides especially useful for treating?

Answer 55

As the antibiotics are lipophilic they can pass through the cell membranes easily They are therefore useful for treating certain infections where bacteria hide from the host's immune system by getting into the host cell

Question 56

What kind of bacterial infections is erythromycin/ clarythromycin useful for treating?

Answer 56

``` Clostridium spp. Streptococcus spp. Staph. aureus Neisseria spp. (partly sensitive) Haemophils infleunzae (partly sensitive) ```

Question 57

Why must gentamicin be given IV?

Answer 57

It is not absorbed from the gut

Question 58

What is gentamicin used to treat?

Answer 58

Active mainly against gram negative aerobic organisms such as coliforms and Pseudomonas aeruginosa Used in hospital for treating serious gram negative infeciton

Question 59

How is gentamicin excreted?

Answer 59

In the urine

Question 60

What can gentamicin cause?

Answer 60

Causes damage to kidneys and VIIIth cranial nerve (deathless and dizziness) so need to monitor blood levels of ahminoglycosides

Question 61

Examples of antibiotics that act on material DNA? (3)

Answer 61

Metronidazole Trimethoprim (+/- sulphonamide) - shown to cause synergy in the lab Fluoroquinolones

Question 62

How can metronidazole be given?

Answer 62

Oral or IV

Question 63

How does metronidazole work?

Answer 63

Causes strand breakage of bacterial DNA

Question 64

What type of infections is metronidazole used to treat?

Answer 64

Anaerobic (and some protozoal) infections

Question 65

How if Trimethoprim given?

Answer 65

Oral

Question 66

How does trimethoprim work?

Answer 66

It inhibits bacterial folic acid synthesis

Question 67

What is the name when trimethoprim is given in combination with sulphamethoxazole? How is this given?

Answer 67

Co-trimoxazole (septrin) | IV or orally

Question 68

How is trimethoprim excreted?

Answer 68

Via the urine

Question 69

What type of bacteria does trimethoprim have activity against?

Answer 69

Some gram negative and some gram positive bacteria

Question 70

What are 2 examples of fluoroquinolones? | How are each given?

Answer 70

Ciprofloxacin (IV, oral) | Levofloxacin (IV)

Question 71

How do fluoroquinolone act?

Answer 71

By preventing "supercoiling of bacterial DNA"

Question 72

Are fluoroquinolones bactericidal or bacterostatic?

Answer 72

Bactericidal

Question 73

Why is the use of Fluoroquinolones severely restricted in tayside?

Answer 73

In an attempt to reduce the risk of clostridium difficile

Question 74

How are fluoroquinolones excreted?

Answer 74

Via the urine

Question 75

What are the common side effects of all antibiotics?

Answer 75

Nausea, vomiting and diarrhoea (all antibiotics disrupt the gut bacterial flora)

Question 76

What antibiotic causes renal and VIII nerve damage?

Answer 76

Gentamicin

Question 77

What antibiotic causes tendonitis?

Answer 77

Ciprofloxacin

Question 78

What antibiotic interacts with alcohol?

Answer 78

Metronidazole

Question 79

What group of antibiotics increase the risk of C. diff. in elderly patients?

Answer 79

Broad spectrum antibiotics

Question 80

What 4 antibiotics do we try to avoid? | Why?

Answer 80

Cephalosporins Co-amoxiclav Ciprofloxacin Clindamycin