Which of the following statements regarding tests for microbial susceptibility to chemotherapeutic agents is false?

• A. The Kirby-Bauer disk diffusion test measures the zone of inhibition to assess susceptibility.
• B. E-test strips can be used to determine the MIC of an antimicrobial agent.
• C. Minimum inhibitory concentration (MIC) tests determine the lowest concentration of an agent that inhibits visible growth.
• D. Susceptibility tests are only performed on viruses and not on bacteria.

Answer: (D)

Verified step by step guidance

1. Understand the context: Microbial susceptibility tests are designed to determine how effective chemotherapeutic agents (like antibiotics) are against microorganisms such as bacteria.
2. Review each statement carefully: The Kirby-Bauer disk diffusion test measures the zone of inhibition around antibiotic disks to assess bacterial susceptibility, which is a true statement.
3. Recognize that E-test strips provide a gradient of antibiotic concentration and can be used to determine the Minimum Inhibitory Concentration (MIC), making that statement true as well.
4. Recall that MIC tests identify the lowest concentration of an antimicrobial agent that visibly inhibits microbial growth, confirming the accuracy of that statement.
5. Identify the false statement: Susceptibility tests are primarily performed on bacteria and some fungi, but not on viruses, because viruses require host cells to grow and are not tested by these methods. Therefore, the statement claiming susceptibility tests are only performed on viruses and not bacteria is false.