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Microbiology (bacteria) > antibiotics > Flashcards

antibiotics Flashcards

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1
Q

what are the seven categories of antibiotics?

A

1 - antimetabolites (sulfonamides)
2 - inhibitors of cell wall synthesis (B-lactams, glycopeptides)
3 - agents that alter membrane permeability (polymyxins, polyenes)
4 - inhibitors of protein synthesis (aminoglycosides, macrolides, tetracycline, chloramphenicol)
5 - inhibitors of DNA replication (quinolone)
6 - inhibitors of RNA replication (rifampin)
7 - miscellaneous antibiotics

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2
Q

what is an antimetabolite?

A

interferes with synthesis of function of a substance involved in normal cell metabolism

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3
Q

mechanism of sulfonamides?

A
  • broad spectrum

- penetrate sensitive bacteria and inhibit production of folic acid through competitive inhibition

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4
Q

why is folic acid important for cell metabolism?

A

bacterial DNA synthesis -

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5
Q

Is the action of sulfonamides reversible?

A

yes - bacteriostatic

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6
Q

name the three antimetabolites we are responsible for.

A

1 - sulfonamides
2 - trimethoprim
3 - isoniazid

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7
Q

trimethoprim action

A
  • synergistic with sulfonamides
  • inhibits enzyme that converts dihydrofolate to tetrahydrofolate
  • used with sulfonamides (sulfamethoxazole) for UTIs
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8
Q

isoniazid action

A
  • narrow spectrum (M. tuberculosis)
  • interferes with mycolic acid synthesis (mycobacteria)
  • bactericidal
  • inhibits enzyme InhA - fatty acid elongation
  • penetrates human cell wall to kill intracellular bacteria
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9
Q

name seven antibiotics that are inhibitors of cell wall synthesis

A 
1 - penicillin
2- cephalosporins
3 - beta-lactam rings but not penicillin
4 - beta-lactamase inhibitors
5 - glycopeptides
6 - cycloserine
7 - bacitracin
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10
Q

why such a large difference in sensitivity between animal cells and bacteria with penicillin?

A

animal cells don’t have a cell wall.

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11
Q

what is a lactam?

A

an anhydride link that forms a ring structure in part of a molecule - strained and easily hydrolyzed

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12
Q

how does penicillin kill cells?

A
  • B-lactam antibiotic
  • bind to and inactivate penicillin binding proteins (PBPs) - which are responsible for terminal stages of cell wall reshaping during growth and division
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13
Q

how can you prevent or slow the lethal action of penicillin?

A

deprive bacteria of nutrients essential for growth. bacteria must be able to divide once or twice.

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14
Q

how can penicillin be hydrolyzed?

A

1 - acidity of the stomach

2 - penicillinases in bacteria

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15
Q

penicillin G is sensitive to:

A

acid hydrolysis and penicillinase

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16
Q

penicillin V is sensitive to:

A

penicillinase only

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17
Q

ampicillin is sensitive to:

A

penicillinase only

18
Q

pencillin G is effective against:

A
  • many gram-positive, sensitive cocci
  • some gram-negative cocci (meningitis)
  • spirochete (treponema pallidum - syphilis)
19
Q

shortcomings of penicillin G

A
  • no oral formulation because acid labile
  • penicillinase sensitivity
  • ## potential allergic response
20
Q

what are some semi-synthetic penicillins and how are they used?

A
  • oxacillin, nafcillin

- used against bacteria that produce penicillinase

21
Q

penicillins that are sensitive to penicillinase and are limited spectrum include:

A
  • penicillin G - acid labile
  • penicillin V - relatively acid stable
  • Penicillin VK - higher solubility
22
Q

penicillins sensitive to penicillinase that are broader spectrum

A
  • ampicillin - acid stable

- amoxicillin - acid stable

23
Q

penicillins sensitive to penicillinase that are extended spectrum (more bacilli, less G+ cocci)

A
  • tricarcillin - b-lactam effective against pseudomonas aeruginosa
  • piperacillin - most active against G- bacilli
24
Q

penicillins resistant to penicillinase

A
  • methicillin - acid labile

- naficillin, dicloxacillin, oxacillin - newer, more potent, acid resistant (oral available)

25
Q

What does MRSA stand for?

A

methicillin resistant staphylococcus aureus

26
Q

penicillin structure

A
  • 4 membered b-lactam ring

- thiazolidine ring

27
Q
  • CWSI - cephalosporin structure
A
  • 4 membered b-lactam ring

- dihydrothiazine ring

28
Q
  • CWSI - cephalosporin characteristics
A
  • also bactericidal (cell wall inhibitor)
  • broad spectrum against G+ and some G- bacilli
  • GREATER acid stability than penicillin
  • resistant to some penicillinases
29
Q

first gen cephalosporins and effectiveness

A
  • cefazolin, cephalexin, cefaclor, cephalothin

- G+ cocci, some G- bacilli, NOT pseudomonas aeruginosa

30
Q

second gen cephalosporins and effectiveness

A
  • cefuroxime, cefamandole, cefonocid, cefotetan, cefoxitin

- less effective against G+, more against G- enterics, still NO P. aeruginosa

31
Q

third gen cephalosporins and effectiveness

A
  • ceftriaxone, ceftazidime, cefotaxime, cefoperazone
  • broader G- spectrum
  • ceftazidime - gets P. aeruginosa
  • ceftriaxone - penetrates CNS
32
Q

CWSI - B-lactam ring antibiotics that are not penicillin include:

A
  • monobactams (aztreonam) - G- and P. aeruginosa

- carbapenems (imipenem) - broadest spectrum and most resistant to most b-lactamases

33
Q

CWSI - 3 B-lactamase inhibitors

A

1 - clavulanic acid - (augmentin - with amoxicillin)
2 - sulbactam (unasyn - with ampicillin)
3 - tazobactam (zosyn - with piperacillin)

34
Q

CWSI - glycopeptides - 2 important drugs

A

1 - vancomycin

2- teicoplanin

35
Q

vancomycin characteristics

A
  • restricted to G+ organisms
  • binds R-D-Ala-D-Ala which blocks peptidoglycan precursor transfer
  • somewhat toxic but used when other drugs are contraindicated
  • ONLY drug available for multiply resistant enterococcus (MRE) and MRSA
36
Q

teicoplanin characteristics

A
  • chemically similar to vancomycin
  • greater lipophilicity - excellent tissue and intracellular phagocytic penetration
  • NO oral formulation, very expensive
  • not approved by FDA yet
37
Q

CWSI - cycloserine

A
  • secondary TB drug

- toxic

38
Q

CWSI - bacitracin

A
  • restricted to G+
  • toxic, topical only
  • found in Neosporin with polymyxin B or neomycin
39
Q

antibiotics that affect membrane permeability contrast to b-lactams

A
  • cell growth not required for activity
40
Q

antibiotics that affect membrane permeability - examples

A

1 - polymyxins B and E: effective against G- enteric rods

2 -

Microbiology (bacteria) (16 decks)

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