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Microbiology > Ch 20: Antimicrobial Drugs > Flashcards

Ch 20: Antimicrobial Drugs Flashcards

1
Q

Define antibiotic (according to the textbook).

A

An antimicrobial agent, usually produced naturally by a bacterium or fungus

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2
Q

Why have pharmaceutical companies put very little investment in the development of new antibiotics?

A
  1. Difficult to identify new mechanisms to kill pathogens
  2. Generate small revenue
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3
Q

What genus produces more than half of our antibiotics?

A

Streptomyces

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4
Q

Are all antibiotics produced by aerobic or anaerobic organisms?

A

Aerobic

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5
Q

What characteristics do almost all antibiotic producing microbes have in common?

A
  1. Gram+ rods
  2. Live in soil
  3. Produce spores
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6
Q

What is the advantage and disadvantage of treating a bacterial infection with a broad spectrum antibiotic?

A
  • Adv: can treat without knowing specific infection
  • Dis: kill off normal microbiota
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7
Q

What organisms are common causes of superinfections? (Cause a second infection during the course of treatment for an existing infection)

A
  1. Clostridium difficile
  2. Candida albicans (yeast)
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8
Q

What is the difference between bacteriocidal and bacteriostatic?

A
  • Bacteriocidal - kills microbes directly
  • Bacteriostatic - prevents microbes from grown
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9
Q

Why is it more difficult to find or develop antimicrobials effective against fungi compared to bacteria?

A
  • More targets for selective toxicity in bacteria
  • Fungi more closely related to humans, so drugs could harm humans
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10
Q

There is concern that antibiotics that target ribosomes could adversely affect host cells. Why?

A

Mitochondria have the same ribosomes as bacteria (70s)

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11
Q

What is a common antimicrobial target in fungal plasma membranes?

A

Ergosterol (equivalent to cholesterol in humans)

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12
Q

Why does penicillin only affect actively growing cells?

A

Stops synthesis of new peptidoglycan

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13
Q

Antimicrobials that target replication and transcription generally have limited medical usefulness. Why?

A

Most interfere with mammalian DNA/RNA

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14
Q

Aside from penicillin, what other antibiotics inhibit peptidoglycan synthesis by inhibiting transpeptidase? (3)

A
  1. Carbapenem
  2. Monobactam
  3. Cephalosporin
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15
Q

What are the similarities and differences between penicillin G vs penicillin V?

A
  • Penicillin G - injection; “gold standard”; most active
  • Penicillin V - oral; less active; rapidly excreted
  • Both - common core; rxn occurs with PBP within β-lactam ring
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16
Q

How do Procaine or Benzathine extend the duration of action of penicillin?

A
  • Distribute into storage tissue to be released slowly into the blood-stream
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17
Q

What are some disadvantages of natural penicillins?

A
  1. Limited to gram-positive bacteria
  2. Susceptible to penicillinases
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18
Q

What advantages do the semisynthetic penicillins oxacillin and ampicillin have over natural penicillin?

A
  • Oxacillin - resistant to penicillinase
  • Ampicillin - extended-spectrum to gram-negative
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19
Q

What is the function of potassium clavulanate when combined with a penicillin?

A

Suicide inhibitor of β-lactamase to prevent degredation of penicllin

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20
Q

Staphylococcal infections rapidly became resistant to penicillin due to a plasmid-borne _____ gene

A

β-lactamase

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21
Q

_____ are a class of β-lactam antibiotics that swaps a “S” in penicillin for a “C”.

A

Carbapenems

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22
Q

Why do carbapenems have the broadest spectrum of activity of β-lactam antibiotics?

A

They selectively get taken up by porins

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23
Q

True or false. Carbapenems are resistant to penicillinases.

A

True

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24
Q

Monobactams are a class of monocyclic β-lactam antibiotics with activity limited to gram-negative bacteria. Why is this?

A

Poorly binds the penicillin-binding proteins of gram-positive and anaerobic bacteria

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25
Q

Activity and β-lactam ring structure of ______ matches penicillin.

A

Cephalosporins

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26
Q

Cephalosporins were developed from cephalosporin C, a natural product of ______.

A

Cephalosporin acreminium

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27
Q

______ is a mixture of related cyclic polypeptides from Bacillus subtilus that interferes with the transport of peptidoglycan precursors NAG and NAM across the plasma membrane, therefore inhibiting cell wall synthesis.

A

Bacitracin

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28
Q

Is bacitracin limited to gram-positive or gram-negative bacteria?

A

Gram-positive

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29
Q

How is bacitracin administered?

A
  • Strictly topically
  • Toxic orally
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30
Q

_____ is a polypeptide inhibitor of cell wall synthesis by binding NAG and NAM subunits to prevent their incorporation into the peptidoglycan matrix.

A

Vancomycin

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31
Q

Is vancomycin limited to gram-positive or gram-negative bacteria?

A

Gram-positive

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32
Q

Vancomycin is derived from what genus of bacteria?

A

Streptomyces

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33
Q

Isoniazid inhibits mycolic acid synthesis and is used to treat _____

A

Active turberculosis

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34
Q

What drugs are often given with Isoniazid to prevent tuberculosis from developing resistance?

A

Rifampin or ethambutol

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35
Q

What is the function of ethambutol (on its own)?

A
  • Inhibits incorporation of mycolic acid into cell walls
  • Comparatively weak on its own
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36
Q

Why is resistance a concern when using a weak antibiotic?

A

Slows growth, but does not kill, which allows for more time for mutations to increase resistance

37
Q

What antibiotic inhibits protein synthesis by binding to the 50s ribosome subunit?

A

Chloramphenicol

38
Q

Why is chloramphenicol inexpensive?

A
  • Simple structure
  • Can be chemically synthesized rather than isolated
39
Q

Is chloramphenicol limited to gram-positive or gram-negative bacteria

40
Q

What antibiotic inhibits protein synthesis by altering the shape of the 30s subunit of ribosomes, causing translation errors?

A

Aminoglycosides

41
Q

What are some examples of aminoglycosides? (4)

A
  1. Streptomycin
  2. Neomycin
  3. Gentamicin
  4. Tobramycin
42
Q

What do the suffixes -mycin and -micin mean?

A
  • -mycin - came from Streptomyces
  • -micin - came from Micromonospora
43
Q

Do aminoglycosides act on gram-positive or gram-negative bacteria?

A

Gram-negative (but not anaerobes)

44
Q

What class of antibiotics bind to 30s ribosomal subunits and interfere with tRNA-codon attachment?

A

Tetracyclines

45
Q

What genus produces tetracyclines?

A

Streptomyces

46
Q

Are tetracyclines limited to gram-positive or gram-negative bacteria?

47
Q

What are some disadvantages of tetracycline? (3)

A
  1. Suprres normal intestinal microbiota
  2. May brown children’s teeth (< 8 years)
  3. Liver damage in pregnant women
48
Q

What class of antibiotic binds to 50s subunit the prevents translocation (blocking exit tunnel).

A
  • Macrolides
  • Named for presence of a macrocyclic lactone ring
49
Q

What macrolide was the first member of its class, with a similar spectrum to penicillin G but can be taken orally?

A

Erythromycin

50
Q

The only approved streptogramin is a mixture of two streptogramins: _____ and _____.

A
  1. Dalfopristin - blocks early translation
  2. Quinopristin - blocks late translation
51
Q

Are streptogramins limited to gram-positive or gram-negative bacteria?

A

Gram-positive

52
Q

______ are a group of totally synthetic antimicrobials that prevent formation of a functional 70s-initiation complex by binding 50s subunit near 30s interface.

A

Oxazolidinones

Ex: linezolid

53
Q

Are oxazolidinones limited to gram-positive or gram-negative bacteria? What organisms is it especially effective against? (2)

A
  • Gram-positive
  • Streptococci and Enterococcithat are resistant to Streptogramins
54
Q

What is the weakness of targeting the fatty acid biosynthetic pathway to kill pathogens?

A

Pathogens don’t have to make fatty acids all the time; they can get them from the host

55
Q

What is the difference between type I and type II fatty acid synthase?

A
  • Type I - Mammalian; 1 giant enzyme that dimerizes)
  • Type II - Bacterial; multiple different enzymes
56
Q

Which antibiotic binds LPS of gram-negative bacteria and alters both the inner and outer membranes, making them more permeable?

A

Polymyxin B

57
Q

What are the components of neosporin? (3)

A
  1. Polymyxin B
  2. Bacitratin
  3. Neomycin
58
Q

What organism produces Polymixin B?

A

Bacillus polymyxa

59
Q

What class of antibiotic is broad-spectrum and inhibits DNA gyrase?

A

Quinolones

60
Q

Why are fluoroquinolones now used instead of quinolones?

A

Nalidixic acid, the first quinolone, was listed as a carcinogen

61
Q

What are fluoroquinolones commonly used to treat?

62
Q

What class of antimicrobial was among the first synthetic antimicrobial produced and interferes with PABA conversion to folate?

A

Sulfonamides (sulfa drugs)

63
Q

Are sulfa drugs bacteriocidal or bacteriostatic? Broad or narrow spectrum?

A
  • Bacteriostatic
  • Broad-spectrum
64
Q

What is the most widely used sulfa drug combination?

A
  • Sulfamethoxazole
  • Trimethoprim

TMP-SMZ

65
Q

Why are only bacteria affected by sulfa drugs?

A
  • Bacteria synthesize folic acid started with PABA
    • Folic acid can’t cross bacterial cell wall
      *
65
Q

Why are only bacteria affected by sulfa drugs?

A
  • Bacteria synthesize folic acid started with PABA
  • Folic acid can’t cross bacterial cell wall
  • Humans ingest folic acid already formed
    • lack enzymes to convert PABA
66
Q

What class of antifungal binds ergosterol and forms transmembrane channels that lead to leakage?

A

Polyenes (polyunsaturated organic acids)

67
Q

What is the most common polyene used as an antifungal? What genus produces it?

A
  • Amphotericin B
  • Streptomyces
68
Q

What class of antifungal inhibits ergosterol synthesis and contains the most widely used antifungal drugs?

69
Q

What are the two subclasses of azoles?

A
  1. Imidazoles
  2. Triazoles
70
Q

What imidazole is an OTC medication that is commonly used to treat athlete’s foot?

A

miconazole

71
Q

What triazole is commonly used for invasive life-threatening fungal infections

A

Fluconazole

72
Q

What class of antifungal inhibits ergosterol synthesis (a different enzyme than azoles)? (2)

A
  • Allylamines - Ex: Terbinafine
  • Thiocarbamates - Ex: Tolnaftate
73
Q

Which fungal cell wall component is the primary target for antifungals?

74
Q

What class of antifungal inhibits the enzyme 1,3-β-glucan synthase? (Ex: caspofungin)

A

Echinocandin

75
Q

What is the function of flucytosine?

A
  • Cytosine analog
  • Inhibitor of thymidine synthase, and thus DNA synthesis
  • Mammalian cells lack flucytosine converting enzyme
76
Q

What antifungal binds to fungal tubulin, interfering with microtubule assembly and subsequently mitosis? What species produces it?

A
  • Griseofulvin
  • Penicillium
77
Q

What antifungal is an organic unsaturated fatty acid that is less effective against athlete’s foot compared to miconazole

A

Undecylenic

78
Q

What antifungal is used to treat Pneumocystis pneumonia (complication of AIDS)?

A

Pentamidine

79
Q

What is the difference between a nucleotide and a nucleoside?

A
  • Nucleoside - a nitrogenous base and a five-carbon carbohydrate group
  • Nucleotide - a nucleoside with one or more phosphate groups attached
80
Q

What antiviral structurally resembles the nucleoside deoxyguanosine and is specifically used for treating herpes virus infections?

81
Q

What two antivirals inhibit neuraminidase of influenza?

A
  • Zanamivir
  • Oseltamivir
82
Q

Common targets for HIV by antivirals include? (4)

A
  1. Reverse transcriptase
  2. Integrase
  3. Protease
  4. Block cell entry
83
Q

Drugs targeting the host cell ______ receptor can be used to block HIV from entering the cell?

84
Q

What antivirals inhibit reverse transcriptase of HIV? (2)

A
  1. Azidothymidine/AZT - nucleoside thymidine analog
  2. Tenofovir - nucleotide adenosine analog
85
Q

What antiprotozoan, isolated form the cinchona tree, is used in the treatment of malaria?

86
Q

What drug selectively targets anaerobic bacteria and protozoa due to their ability to reduce metronidazole, causing it to covalently bind to DNA?

A

Metronidazole

87
Q

Tetracycline sometimes interferes with the activity of penicillin. How?

A
  • Tetracycline is bacteriostatic
  • Penicillin only targets growing cells

Microbiology (19 decks)

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