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): "Human cells make drug efflux pumps." Understand that efflux pumps are membrane proteins that actively expel toxic substances, including drugs, from cells. Both bacterial and human cells can have efflux pumps, but their roles and specific types differ. Confirm whether human cells indeed produce efflux pumps and clarify their function in human cells.
2. Step 2: Evaluate statement (b): "The minimum bactericidal concentration is the minimum concentration of the drug that kills at least 50 percent of the bacteria present." Recall the definition of minimum bactericidal concentration (MBC), which is the lowest concentration of an antimicrobial that kills a defined percentage of bacteria, typically 99.9%. Compare this with the statement and identify the error.
3. Step 3: Evaluate statement (c): "The E-test can reveal if a drug is bactericidal or bacteriostatic." Understand what the E-test measures: it determines the minimum inhibitory concentration (MIC) of an antibiotic. Consider whether the E-test alone can distinguish between bactericidal and bacteriostatic effects, and explain why or why not.
4. Step 4: Evaluate statement (d): "A drug that is bactericidal at one dose may be bacteriostatic at another dose." Consider the dose-dependent effects of antimicrobial drugs and whether the same drug can have different effects at different concentrations. Confirm the truthfulness of this statement and explain the concept.
5. Step 5: Evaluate statement (e): "The antifolate combination therapy trimethoprim-sulfamethoxazole may be used to treat protozoan infections." Recall the spectrum of activity of trimethoprim-sulfamethoxazole, including its use against certain protozoa such as Pneumocystis jirovecii. Confirm the accuracy of this statement and clarify its clinical relevance.

Key Concepts

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 drugs, human cells also possess efflux pumps, such as P-glycoprotein, which help protect tissues by removing harmful compounds. Understanding their presence in both cell types is crucial for interpreting drug resistance and pharmacokinetics.

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.

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 between bactericidal and bacteriostatic effects.