Lecture #10

Question 1

What is the primary goal of antimicrobial chemotherapy?

Answer 1

Destroy infective agents without harming host cells.

Question 2

What are the ideal characteristics of an antimicrobial drug?

Answer 2

• Toxic to microbes, not host cells
• Microbicidal, not microbistatic
• Soluble and effective in body fluids
• Long-lasting potency without premature breakdown
• Does not promote antimicrobial resistance
• Supports host defenses
• Remains active in tissues and body fluids
• Delivered effectively to infection site
• Avoids allergies or secondary infections to the host

Question 3

Define narrow-spectrum antimicrobials.

Answer 3

Effective against specific microbes.

Question 4

Define broad-spectrum antimicrobials.

Answer 4

Effective against a wide range of microbes.

Question 5

What three factors should be considered before therapy begins?

Answer 5

• Identity of the microorganism
• Microorganism’s drug susceptibility
• Patient’s medical condition

Question 6

What is the Kirby-Bauer Technique used for?

Answer 6

Measures zone of inhibition on agar plates.

Question 7

What does the Tube Dilution Test determine?

Answer 7

Minimum Inhibitory Concentration (MIC).

Question 8

What does the Therapeutic Index (TI) represent?

Answer 8

Ratio of toxic dose to therapeutic dose.

Question 9

How is a higher Therapeutic Index (TI) interpreted?

Answer 9

Safer drug.

Question 10

What preexisting conditions must be considered before prescribing an antibiotic?

Answer 10

• Preexisting conditions that might influence drug activity
• History of allergy to a certain class of drugs
• Underlying liver or kidney disease
• Special precautions for infants, the elderly, and pregnant women
• Intake of other drugs that can increase toxicity

Question 11

What is the goal of antimicrobial drugs?

Answer 11

Selectively toxic: kill or inhibit microbial cells without damaging host tissues.

Question 12

What are the categories of mechanisms of drug action?

Answer 12

• Inhibit cell wall synthesis
• Inhibit nucleic acid synthesis
• Inhibit protein synthesis
• Disrupt cytoplasmic membrane
• Inhibit folic acid synthesis

Question 13

Name a drug that targets the cell wall.

Answer 13

• Penicillins
• Cephalosporins
• Carbapenems

Question 14

What do aminoglycosides do?

Answer 14

Cause misreading of the mRNA.

Question 15

What is the action of tetracyclines?

Answer 15

Block the attachment of tRNA on the A acceptor site.

Question 16

What do macrolides inhibit?

Answer 16

Inhibit translocation of the subunit during translation.

Question 17

What do fluoroquinolones target?

Answer 17

Inhibit DNA unwinding enzymes of helicases.

Question 18

What do polymyxins interact with?

Answer 18

Membrane phospholipids; distort the cell surface.

Question 19

What is a broad-spectrum antibiotic?

Answer 19

Effective against multiple bacterial groups.

Question 20

What is a narrow-spectrum antibiotic?

Answer 20

Targets specific bacteria.

Question 21

Name an agent used to treat fungal infections.

Answer 21

• Macrolide Polyenes: Amphotericin B
• Azoles: Ketoconazole, fluconazole, clotrimazole
• Echinocandins: Micafungin, caspofungin
• Allylamines: Terbinafine, naftifine

Question 22

What is metronidazole used for?

Answer 22

Widely used amoebicide; also treats Giarda Lamblia and Trichomonas Vaginalis.

Question 23

What is a significant challenge when treating viral infections?

Answer 23

Disrupting viral metabolism requires disruption of host cellular metabolism.

Question 24

What are some agents that inhibit virus entry?

Answer 24

• Enfuvirtide
• Amantadine

Question 25

What are the causes of antimicrobial resistance?

Answer 25

* Spontaneous mutations in critical chromosomal genes * Horizontal gene transfer * Slowing or stopping of metabolism

Question 26

What are common mechanisms of drug resistance?

Answer 26

* Enzymes inactivate drugs * Decreased drug uptake * Drug elimination via pumps * Altered drug binding sites * Alternative metabolic pathways

Question 27

What is the consequence of natural selection in microbial populations?

Answer 27

Drug-resistant populations have a selective advantage.

Question 28

What is the urgent problem regarding antimicrobial resistance?

Answer 28

We may enter a postantibiotic era where some infections will be untreatable.

Question 29

What is one new approach to antimicrobial therapy?

Answer 29

Using RNA interference strategies.

Question 30

What are the adverse effects of antimicrobials?

Answer 30

* Toxicity affecting various systems * Superinfections from resistant microbes

Question 31

What is the issue with broad-spectrum antimicrobial therapy?

Answer 31

Leads to superinfections and other adverse reactions.

Question 32

What is the safest antibiotic based on Therapeutic Index?

Answer 32

Drug B (TI = 12).

Question 33

What is the least toxic mode of action for antibiotics?

Answer 33

Acts on peptidoglycan cell wall.