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Ch. 15 - Antimicrobial Drugs
Norman-McKay- Microbiology: Basic and Clinical Principles 2nd Edition
Norman-McKay2nd EditionMicrobiology: Basic and Clinical PrinciplesISBN: 9780137661619Not the one you use?Change textbook
All textbooksNorman-McKay 2nd EditionCh. 15 - Antimicrobial DrugsProblem 14
Chapter 15, Problem 14

Mark the following as true or false, and then correct the false statements so they are true.
a. Human cells make drug efflux pumps.
b. The minimum bactericidal concentration is the minimum concentration of the drug that kills at least 50 percent of the bacteria present.
c. The E-test can reveal if a drug is bactericidal or bacteriostatic.
d. A drug that is bactericidal at one dose may be bacteriostatic at another dose.
e. The antifolate combination therapy trimethoprim-sulfamethoxazole may be used to treat protozoan infections.

Verified step by step guidance
1
Step 1: Evaluate statement (a) - Consider whether human cells produce drug efflux pumps. Recall that efflux pumps are membrane proteins that bacteria use to expel toxic substances, including antibiotics, but similar mechanisms can exist in human cells for drug metabolism and resistance. Determine if this statement is true or false based on this understanding.
Step 2: Evaluate statement (b) - Understand the definition of minimum bactericidal concentration (MBC). MBC is the lowest concentration of an antimicrobial that kills a defined percentage of bacteria, but verify if that percentage is 50% or another value. If false, correct the statement with the accurate definition.
Step 3: Evaluate statement (c) - Review what the E-test measures. The E-test determines the minimum inhibitory concentration (MIC) of a drug against bacteria. Consider whether it can distinguish between bactericidal and bacteriostatic effects, and if not, correct the statement accordingly.
Step 4: Evaluate statement (d) - Analyze the relationship between drug dose and its bactericidal or bacteriostatic effect. Determine if a drug can act as bactericidal at one concentration and bacteriostatic at another, and confirm if this statement is true or false.
Step 5: Evaluate statement (e) - Consider the spectrum of activity of the antifolate combination trimethoprim-sulfamethoxazole. Determine if it is used to treat protozoan infections and correct the statement if necessary.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Drug Efflux Pumps in Human and Bacterial Cells

Drug efflux pumps are membrane proteins that expel toxic substances, including antibiotics, out of cells. While bacteria commonly use efflux pumps to resist antibiotics, human cells also possess efflux pumps, such as P-glycoprotein, which help protect tissues by removing drugs and toxins. Understanding their presence in both cell types is key to interpreting drug resistance and pharmacokinetics.
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Minimum Bactericidal Concentration (MBC)

The Minimum Bactericidal Concentration is the lowest concentration of an antimicrobial agent required to kill a defined percentage of bacteria, typically 99.9%, not 50%. It differs from the Minimum Inhibitory Concentration (MIC), which inhibits growth but may not kill bacteria. MBC helps determine the killing efficacy of antibiotics.
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Bactericidal vs. Bacteriostatic Effects and Dose Dependency

Bactericidal drugs kill bacteria, while bacteriostatic drugs inhibit bacterial growth without killing. Some drugs can act as bactericidal at higher doses and bacteriostatic at lower doses, depending on concentration and bacterial species. Tests like the E-test measure MIC but do not directly distinguish bactericidal from bacteriostatic effects.
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Related Practice
Textbook Question

Acquired antibiotic resistance can include all of the following except:

a. Altering an enzyme that a given drug may target

b. Making endospores

c. Altering a point of entry for a drug

d. Making enzymes that inactivate a drug

e. Increasing the number of efflux pumps that are active in a cell

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Textbook Question

Why is it challenging to obtain selectively toxic drugs against fungi, protozoans, and viruses?

885
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Textbook Question

Choose the false statement(s). Select all that apply.

a. Antifungal drugs may target cholesterol in fungal cell membranes.

b. Azole and polyene drugs promote cell lysis by impacting fungal cell plasma membranes.

c. Echinocandin drugs inhibit fungal cell wall synthesis.

d. Antifungal drugs may target DNA replication.

e. Antifungal drugs may target protein synthesis.

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Textbook Question

If a gene encoding a bacterial transpeptidase enzyme undergoes mutation, which of the following antimicrobials may no longer be effective against the mutated bacterium?

a. Macrolides

b. Polypeptide drugs

c. Tetracyclines

d. Penicillins

e. Quinolones

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Textbook Question

Assume a clinical sample yields a strain of S. aureus containing a plasmid that encodes two antimicrobial-resistance genes. How did the bacterium most likely acquire these new resistance genes?

a. The strain was intrinsically resistant.

b. The strain obtained the genes through horizontal gene transfer.

c. The strain acquired the genes by a random mutation.

d. The strain picked up the genes by an efflux pump.

e. The strain acquired the genes through cell division events.

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Textbook Question

Match the antimicrobial drug to its feature. Some features may be used more than once, and some may not be used at all.

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