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Flashcards in *Microbiology 3 (lecture 5) Deck (80):
1

What is the difference between bactericidal and bacteriostatic antibiotics?

Bactericidal = kill bacteria
Bcteriostatic = inhibit bacterial growth

2

Why must antibiotics be selectively toxic?

In order to kill the bacteria without damaging the host

3

How are antibiotics usually administered?

Usually orally or IV (rarely intramuscularly)

4

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

Approx. 1 hour later
Within 15 minutes

5

Where are antibiotics excreted?

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

6

Why are antibiotics sometimes given in combination? (3)

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

7

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

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

8

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

The penicillins
The cephalosporins
The glycopeptides

9

Name the 6 penicillins?

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

10

Name a cephalosporin?

Ceftriaxone

11

Name 2 glycopeptides?

Vancomycin
Teicoplanin

12

How do the penicillins work?

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

13

Are the penicillins bactericidal or bacteriostatic?

Bactericidial

14

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

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

15

Are the penicillins safe in pregnancy?

Yes

16

What are the 2 main drawbacks of the penicillins?

-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

17

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

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

18

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

Yes

19

What does the penicillin nucleus look like?

A house and a garage

20

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

Flucloxacillin (IV, oral)

21

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

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

22

What penicillin is given to gram negative organisms?

Temocillin (IV only)

23

How is flucloxacillin given?

IV and oral

24

Spectrum of flucloaxicillin?

Very narrow
Useful only for staphylococci and streptococci)

25

What is flucloxacillin used to treat?

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

26

How can amoxicillin be given?

IV, oral

27

Why has amoxicillin become less effective over the years?

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

28

What is co-amoxiclav?
When is it used?

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

29

How can co-amoxiclav be given?

oral and IV

30

What is tazocin made up of?

Piperacillin (antibiotic)
Tazobactam (beta-lactamase inhibitor)

31

How is tazocin given?

IV only

32

How is temocillin given?

IV only

33

What type of bacteria can temocillin be used to treat?

Colifroms

34

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

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

35

What do all cephalosporins have in their name?

"ceph" or "cef"

36

How do cephalosporins work?
Bactericidal or bacteriostatic?

inhibit cell wall synthesis and are bactericidal (like penicillins)

37

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

Excreted via kidneys and urine
Few side effects
Safe in pregnancy

38

Appearance of a cephalosporin nucleus?

House + garage + garden

39

Do cephalosporins have a broad or narrow spectrum?

Broad-spectrum

40

What is the major disadvantage of cephalosporins?

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

41

How are the glycopeptides (vancomycin and teicoplanin) given?

Both IV

42

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

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

43

How are the glycopeptides excreted?

Via the kidneys and urine

44

What can happen to patients taking vancomycin with kidney failure?

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

45

What type of organisms are glycoproteins active against?

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

46

What antibiotic can treat MRSA?

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

47

Antibiotics that inhibit protein synthesis? (5)

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

48

What are 3 macrolides?

Erythromycin
Clarythromycin
Azinthromycin

49

What is an example of a teracycline?

Doxycycline

50

What is an example of an aminoglycoside?

Gentamicin

51

How do antibiotics inhibit protein synthesis?

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

52

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

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

53

How are the macrocodes excreted?

Via the liver, biliary tract and into the gut

54

Is Erythromycin safe in pregnancy?

Yes

55

What type of infections are macrolides especially useful for treating?

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

56

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

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

57

Why must gentamicin be given IV?

It is not absorbed from the gut

58

What is gentamicin used to treat?

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

59

How is gentamicin excreted?

In the urine

60

What can gentamicin cause?

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

61

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

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

62

How can metronidazole be given?

Oral or IV

63

How does metronidazole work?

Causes strand breakage of bacterial DNA

64

What type of infections is metronidazole used to treat?

Anaerobic (and some protozoal) infections

65

How if Trimethoprim given?

Oral

66

How does trimethoprim work?

It inhibits bacterial folic acid synthesis

67

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

Co-trimoxazole (septrin)
IV or orally

68

How is trimethoprim excreted?

Via the urine

69

What type of bacteria does trimethoprim have activity against?

Some gram negative and some gram positive bacteria

70

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

Ciprofloxacin (IV, oral)
Levofloxacin (IV)

71

How do fluoroquinolone act?

By preventing "supercoiling of bacterial DNA"

72

Are fluoroquinolones bactericidal or bacterostatic?

Bactericidal

73

Why is the use of Fluoroquinolones severely restricted in tayside?

In an attempt to reduce the risk of clostridium difficile

74

How are fluoroquinolones excreted?

Via the urine

75

What are the common side effects of all antibiotics?

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

76

What antibiotic causes renal and VIII nerve damage?

Gentamicin

77

What antibiotic causes tendonitis?

Ciprofloxacin

78

What antibiotic interacts with alcohol?

Metronidazole

79

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

Broad spectrum antibiotics

80

What 4 antibiotics do we try to avoid?
Why?

Cephalosporins
Co-amoxiclav
Ciprofloxacin
Clindamycin