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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
Activity and β-lactam ring structure of ______ matches penicillin.
Cephalosporins
26
Cephalosporins were developed from cephalosporin C, a natural product of \_\_\_\_\_\_.
*Cephalosporin acreminium*
27
\_\_\_\_\_\_ 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.
Bacitracin
28
Is bacitracin limited to gram-positive or gram-negative bacteria?
Gram-positive
29
How is bacitracin administered?
* Strictly topically * Toxic orally
30
\_\_\_\_\_ is a polypeptide inhibitor of cell wall synthesis by binding NAG and NAM subunits to prevent their incorporation into the peptidoglycan matrix.
Vancomycin
31
Is vancomycin limited to gram-positive or gram-negative bacteria?
Gram-positive
32
Vancomycin is derived from what genus of bacteria?
*Streptomyces*
33
Isoniazid inhibits mycolic acid synthesis and is used to treat \_\_\_\_\_
Active turberculosis
34
What drugs are often given with Isoniazid to prevent tuberculosis from developing resistance?
Rifampin or ethambutol
35
What is the function of ethambutol (on its own)?
* Inhibits incorporation of mycolic acid into cell walls * Comparatively weak on its own
36
Why is resistance a concern when using a weak antibiotic?
Slows growth, but does not kill, which allows for more time for mutations to increase resistance
37
What antibiotic inhibits protein synthesis by binding to the 50s ribosome subunit?
Chloramphenicol
38
Why is chloramphenicol inexpensive?
* Simple structure * Can be chemically synthesized rather than isolated
39
Is chloramphenicol limited to gram-positive or gram-negative bacteria
Both
40
What antibiotic inhibits protein synthesis by altering the shape of the 30s subunit of ribosomes, causing translation errors?
Aminoglycosides
41
What are some examples of aminoglycosides? (4)
1. Streptomycin 2. Neomycin 3. Gentamicin 4. Tobramycin
42
What do the suffixes -mycin and -micin mean?
* -mycin - came from *Streptomyces* * -micin - came from *Micromonospora*
43
Do aminoglycosides act on gram-positive or gram-negative bacteria?
Gram-negative (but not anaerobes)
44
What class of antibiotics bind to 30s ribosomal subunits and interfere with tRNA-codon attachment?
Tetracyclines
45
What genus produces tetracyclines?
*Streptomyces*
46
Are tetracyclines limited to gram-positive or gram-negative bacteria?
Both
47
What are some disadvantages of tetracycline? (3)
1. Suprres normal intestinal microbiota 2. May brown children's teeth (\< 8 years) 3. Liver damage in pregnant women
48
What class of antibiotic binds to 50s subunit the prevents translocation (blocking exit tunnel).
* Macrolides * Named for presence of a macrocyclic lactone ring
49
What macrolide was the first member of its class, with a similar spectrum to penicillin G but can be taken orally?
Erythromycin
50
The only approved streptogramin is a mixture of two streptogramins: _____ and \_\_\_\_\_.
1. Dalfopristin - blocks early translation 2. Quinopristin - blocks late translation
51
Are streptogramins limited to gram-positive or gram-negative bacteria?
Gram-positive
52
\_\_\_\_\_\_ are a group of totally synthetic antimicrobials that prevent formation of a functional 70s-initiation complex by binding 50s subunit near 30s interface.
Oxazolidinones Ex: linezolid
53
Are oxazolidinones limited to gram-positive or gram-negative bacteria? What organisms is it especially effective against? (2)
* Gram-positive * *Streptococci* and *Enterococci*that are resistant to Streptogramins
54
What is the weakness of targeting the fatty acid biosynthetic pathway to kill pathogens?
Pathogens don't have to make fatty acids all the time; they can get them from the host
55
What is the difference between type I and type II fatty acid synthase?
* Type I - Mammalian; 1 giant enzyme that dimerizes) * Type II - Bacterial; multiple different enzymes
56
Which antibiotic binds LPS of gram-negative bacteria and alters both the inner and outer membranes, making them more permeable?
Polymyxin B
57
What are the components of neosporin? (3)
1. Polymyxin B 2. Bacitratin 3. Neomycin
58
What organism produces Polymixin B?
*Bacillus polymyxa*
59
What class of antibiotic is broad-spectrum and inhibits DNA gyrase?
Quinolones
60
Why are fluoroquinolones now used instead of quinolones?
Nalidixic acid, the first quinolone, was listed as a carcinogen
61
What are fluoroquinolones commonly used to treat?
UTI
62
What class of antimicrobial was among the first synthetic antimicrobial produced and interferes with PABA conversion to folate?
Sulfonamides (sulfa drugs)
63
Are sulfa drugs bacteriocidal or bacteriostatic? Broad or narrow spectrum?
* Bacteriostatic * Broad-spectrum
64
What is the most widely used sulfa drug combination?
* Sulfamethoxazole * Trimethoprim TMP-SMZ
65
Why are only bacteria affected by sulfa drugs?
* Bacteria synthesize folic acid started with PABA * Folic acid can't cross bacterial cell wall *
65
Why are only bacteria affected by sulfa drugs?
* 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
What class of antifungal binds ergosterol and forms transmembrane channels that lead to leakage?
Polyenes (polyunsaturated organic acids)
67
What is the most common polyene used as an antifungal? What genus produces it?
* Amphotericin B * *Streptomyces*
68
What class of antifungal inhibits ergosterol synthesis and contains the most widely used antifungal drugs?
Azoles
69
What are the two subclasses of azoles?
1. Imidazoles 2. Triazoles
70
What imidazole is an OTC medication that is commonly used to treat athlete's foot?
miconazole
71
What triazole is commonly used for invasive life-threatening fungal infections
Fluconazole
72
What class of antifungal inhibits ergosterol synthesis (a different enzyme than azoles)? (2)
* Allylamines - Ex: Terbinafine * Thiocarbamates - Ex: Tolnaftate
73
Which fungal cell wall component is the primary target for antifungals?
β-glucan
74
What class of antifungal inhibits the enzyme 1,3-β-glucan synthase? (Ex: caspofungin)
Echinocandin
75
What is the function of flucytosine?
* Cytosine analog * Inhibitor of thymidine synthase, and thus DNA synthesis * Mammalian cells lack flucytosine converting enzyme
76
What antifungal binds to fungal tubulin, interfering with microtubule assembly and subsequently mitosis? What species produces it?
* Griseofulvin * *Penicillium*
77
What antifungal is an organic unsaturated fatty acid that is less effective against athlete's foot compared to miconazole
Undecylenic
78
What antifungal is used to treat *Pneumocystis* pneumonia (complication of AIDS)?
Pentamidine
79
What is the difference between a nucleotide and a nucleoside?
* Nucleoside - a nitrogenous base and a five-carbon carbohydrate group * Nucleotide - a nucleoside with one or more phosphate groups attached
80
What antiviral structurally resembles the nucleoside deoxyguanosine and is specifically used for treating herpes virus infections?
Acyclovir
81
What two antivirals inhibit neuraminidase of influenza?
* Zanamivir * Oseltamivir
82
Common targets for HIV by antivirals include? (4)
1. Reverse transcriptase 2. Integrase 3. Protease 4. Block cell entry
83
Drugs targeting the host cell ______ receptor can be used to block HIV from entering the cell?
CCR5
84
What antivirals inhibit reverse transcriptase of HIV? (2)
1. Azidothymidine/AZT - nucleoside thymidine analog 2. Tenofovir - nucleotide adenosine analog
85
What antiprotozoan, isolated form the cinchona tree, is used in the treatment of malaria?
Quinine
86
What drug selectively targets anaerobic bacteria and protozoa due to their ability to reduce metronidazole, causing it to covalently bind to DNA?
Metronidazole
87
Tetracycline sometimes interferes with the activity of penicillin. How?
* Tetracycline is bacteriostatic * Penicillin only targets growing cells

Microbiology (19 decks)

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