14.E: Antimicrobial Drugs (Exercises)
14.1: Discovering Antimicrobial Drugs
Antimicrobial drugs produced by purposeful fermentation and/or contained in plants have been used as traditional medicines in many cultures for millennia. The purposeful and systematic search for a chemical “magic bullet” that specifically target infectious microbes was initiated by Paul Ehrlich in the early 20th century. The discovery of the natural antibiotic, penicillin, by Alexander Fleming in 1928 started the modern age of antimicrobial discovery and research.
Multiple Choice
A scientist discovers that a soil bacterium he has been studying produces an antimicrobial that kills gram-negative bacteria. She isolates and purifies the antimicrobial compound, then chemically converts a chemical side chain to a hydroxyl group. When she tests the antimicrobial properties of this new version, she finds that this antimicrobial drug can now also kill gram-positive bacteria. The new antimicrobial drug with broad-spectrum activity is considered to be which of the following?
- resistant
- semisynthetic
- synthetic
- natural
- Answer
-
B
Which of the following antimicrobial drugs is synthetic?
- sulfanilamide
- penicillin
- actinomycin
- neomycin
- Answer
-
A
Fill in the Blank
The group of soil bacteria known for their ability to produce a wide variety of antimicrobials is called the ________.
- Answer
-
actinomycetes
Short Answer
Where do antimicrobials come from naturally? Why?
Why was Salvarsan considered to be a “magic bullet” for the treatment of syphilis?
Critical Thinking
In nature, why do antimicrobial-producing microbes commonly also have antimicrobial resistance genes?
14.2: Antibacterial Drugs
Antimicrobial drugs can be bacteriostatic or bactericidal, and these characteristics are important considerations when selecting the most appropriate drug. The use of narrow-spectrum antimicrobial drugs is preferred in many cases to avoid superinfection and the development of antimicrobial resistance. Broad-spectrum antimicrobial use is warranted for serious systemic infections when there is no time to determine the causative agent or when narrow-spectrum antimicrobials fail.
Multiple Choice
Which of the following combinations would most likely contribute to the development of a superinfection?
- long-term use of narrow-spectrum antimicrobials
- long-term use of broad-spectrum antimicrobials
- short-term use of narrow-spectrum antimicrobials
- short-term use of broad-spectrum antimicrobials
- Answer
-
B
Which of the following routes of administration would be appropriate and convenient for home administration of an antimicrobial to treat a systemic infection?
- oral
- intravenous
- topical
- parenteral
- Answer
-
A
Which clinical situation would be appropriate for treatment with a narrow-spectrum antimicrobial drug?
- treatment of a polymicrobic mixed infection in the intestine
- prophylaxis against infection after a surgical procedure
- treatment of strep throat caused by culture identified Streptococcus pyogenes
- empiric therapy of pneumonia while waiting for culture results
- Answer
-
C
Fill in the Blank
The bacterium known for causing pseudomembranous colitis, a potentially deadly superinfection, is ________.
- Answer
-
Clostridium difficile
True/False
Narrow-spectrum antimicrobials are commonly used for prophylaxis following surgery.
- Answer
-
False
Short Answer
When prescribing antibiotics, what aspects of the patient’s health history should the clinician ask about and why?
When is using a broad-spectrum antimicrobial drug warranted?
Critical Thinking
Why are yeast infections a common type of superinfection that results from long-term use of broad-spectrum antimicrobials?
Too often patients will stop taking antimicrobial drugs before the prescription is finished. What are factors that cause a patient to stop too soon, and what negative impacts could this have?
14.3: Drugs Targeting Other Microorganisms
Antibacterial compounds exhibit selective toxicity, largely due to differences between prokaryotic and eukaryotic cell structure. Cell wall synthesis inhibitors, including the β-lactams, the glycopeptides, and bacitracin, interfere with peptidoglycan synthesis, making bacterial cells more prone to osmotic lysis. There are a variety of broad-spectrum, bacterial protein synthesis inhibitors that selectively target the prokaryotic 70S ribosome, including those that bind to the 30S and 50S subunits.
Multiple Choice
Which of the following terms refers to the ability of an antimicrobial drug to harm the target microbe without harming the host?
- mode of action
- therapeutic level
- spectrum of activity
- selective toxicity
- Answer
-
D
Which of the following is not a type of β-lactam antimicrobial?
- penicillins
- glycopeptides
- cephalosporins
- monobactams
- Answer
-
B
Which of the following does not bind to the 50S ribosomal subunit?
- tetracyclines
- lincosamides
- macrolides
- chloramphenicol
- Answer
-
A
Which of the following antimicrobials inhibits the activity of DNA gyrase?
- polymyxin B
- clindamycin
- nalidixic acid
- rifampin
- Answer
-
C
Fill in the Blank
Selective toxicity antimicrobials are easier to develop against bacteria because they are ________ cells, whereas human cells are eukaryotic.
- Answer
-
prokaryotic
True/False
β-lactamases can degrade vancomycin.
- Answer
-
false
Short Answer
If human cells and bacterial cells perform transcription, how are the rifamycins specific for bacterial infections?
What bacterial structural target would make an antibacterial drug selective for gram-negative bacteria? Provide one example of an antimicrobial compound that targets this structure.
Critical Thinking
In considering the cell structure of prokaryotes compared with that of eukaryotes, propose one possible reason for side effects in humans due to treatment of bacterial infections with protein synthesis inhibitors.
14.4: Clinical Considerations
Because fungi, protozoans, and helminths are eukaryotic organisms like human cells, it is more challenging to develop antimicrobial drugs that specifically target them. Similarly, it is hard to target viruses because human viruses replicate inside of human cells.
Multiple Choice
Which of the following is not an appropriate target for antifungal drugs?
- ergosterol
- chitin
- cholesterol
- β(1→3) glucan
- Answer
-
C
Which of the following drug classes specifically inhibits neuronal transmission in helminths?
- quinolines
- avermectins
- amantadines
- imidazoles
- Answer
-
B
Which of the following is a nucleoside analog commonly used as a reverse transcriptase inhibitor in the treatment of HIV?
- acyclovir
- ribavirin
- adenine-arabinoside
- azidothymidine
- Answer
-
D
Which of the following is an antimalarial drug that is thought to increase ROS levels in target cells?
- artemisinin
- amphotericin b
- praziquantel
- pleconaril
- Answer
-
A
Fill in the Blank
Antiviral drugs, like Tamiflu and Relenza, that are effective against the influenza virus by preventing viral escape from host cells are called ________.
- Answer
-
neuraminidase inhibitors
True/False
Echinocandins, known as “penicillin for fungi,” target β(1→3) glucan in fungal cell walls.
- Answer
-
true
Short Answer
How does the biology of HIV necessitate the need to treat HIV infections with multiple drugs?
Niclosamide is insoluble and thus is not readily absorbed from the stomach into the bloodstream. How does the insolubility of niclosamide aid its effectiveness as a treatment for tapeworm infection?
Critical Thinking
Which of the following molecules is an example of a nucleoside analog?
Why can’t drugs used to treat influenza, like amantadines and neuraminidase inhibitors, be used to treat a wider variety of viral infections?
14.5: Testing the Effectiveness of Antimicrobials
Antimicrobial resistance is on the rise and is the result of selection of drug-resistant strains in clinical environments, the overuse and misuse of antibacterials, the use of subtherapeutic doses of antibacterial drugs, and poor patient compliance with antibacterial drug therapies. Drug resistance genes are often carried on plasmids or in transposons that can undergo vertical transfer easily and between microbes through horizontal gene transfer.
Multiple Choice
Which of the following resistance mechanisms describes the function of β-lactamase?
- efflux pump
- target mimicry
- drug inactivation
- target overproduction
- Answer
-
C
Which of the following resistance mechanisms is commonly effective against a wide range of antimicrobials in multiple classes?
- efflux pump
- target mimicry
- target modification
- target overproduction
- Answer
-
A
Which of the following resistance mechanisms is the most nonspecific to a particular class of antimicrobials?
- drug modification
- target mimicry
- target modification
- efflux pump
- Answer
-
D
Which of the following types of drug-resistant bacteria do not typically persist in individuals as a member of their intestinal microbiota?
- MRSA
- VRE
- CRE
- ESBL-producing bacteria
- Answer
-
A
Fill in the Blank
Staphylococcus aureus , including MRSA strains, may commonly be carried as a normal member of the ________ microbiota in some people.
- Answer
-
nasal
Short Answer
Why does the length of time of antimicrobial treatment for tuberculosis contribute to the rise of resistant strains?
What is the difference between multidrug resistance and cross-resistance?
14.6: The Emergence of Drug Resistance
The Kirby-Bauer disk diffusion test helps determine the susceptibility of a microorganism to various antimicrobial drugs. However, the zones of inhibition measured must be correlated to known standards to determine susceptibility and resistance, and do not provide information on bactericidal versus bacteriostatic activity, or allow for direct comparison of drug potencies. Antibiograms are useful for monitoring local trends in antimicrobial resistance/susceptibility.
Multiple Choice
In the Kirby-Bauer disk diffusion test, the _______ of the zone of inhibition is measured and used for interpretation.
- diameter
- microbial population
- circumference
- depth
- Answer
-
A
Which of the following techniques cannot be used to determine the minimum inhibitory concentration of an antimicrobial drug against a particular microbe?
- Etest
- microbroth dilution test
- Kirby-Bauer disk diffusion test
- macrobroth dilution test
- Answer
-
C
The utility of an antibiogram is that it shows antimicrobial susceptibility trends
- over a large geographic area.
- for an individual patient.
- in research laboratory strains.
- in a localized population.
- Answer
-
D
Fill in the Blank
The method that can determine the MICs of multiple antimicrobial drugs against a microbial strain using a single agar plate is called the ________.
- Answer
-
Etest
True/False
If drug A produces a larger zone of inhibition than drug B on the Kirby-Bauer disk diffusion test, drug A should always be prescribed.
- Answer
-
false
Short Answer
How is the information from a Kirby-Bauer disk diffusion test used for the recommendation of the clinical use of an antimicrobial drug?
What is the difference between MIC and MBC?
Critical Thinking
Can an Etest be used to find the MBC of a drug? Explain.
14.7: Current Strategies for Antimicrobial Discovery
With the continued evolution and spread of antimicrobial resistance, and now the identification of pan-resistant bacterial pathogens, the search for new antimicrobials is essential for preventing the postantibiotic era.
Multiple Choice
Which of the following has yielded compounds with the most antimicrobial activity?
- water
- air
- volcanoes
- soil
- Answer
-
D
True/False
The rate of discovery of antimicrobial drugs has decreased significantly in recent decades.
- Answer
-
true
Critical Thinking
Who should be responsible for discovering and developing new antibiotics? Support your answer with reasoning.