Which of the following statements regarding a viral plaque assay is correct?

Question

Which of the following statements regarding a viral plaque assay is correct?

BlackTom AI · Accepted Answer

First, let's lay out what the question is asking and what the options claim about a viral plaque assay.
Option 1: 'To ensure accuracy, wells with between 10-100 plaques should be counted.' This statement attempts to describe a counting guideline, but plaque assay guidelines typically target a wider and more standard range (such as 30-300 plaques) to balance statistical reliability and counting practicality. If a plate has too few plaques, random error increases; if too many, overlapping plaques make counting unreliable. Therefore this option is not the best general guideline and is commonly considered inaccurate in standard protocols.
Option 2: 'In a plaque assay the amount of virus per well remains constant, but the amount of media changes in each well.' In a typical plaque assay, you serially dilute the virus inoculum across wells, so the amount of virus present in each well varies by dilution. The volume of media is usually kept constant across wells (except for specific experimental designs), while the viral dose changes due to dilution. This makes the statement misleading and incorrect for standard plaque assays.
Option 3: 'Crystal violet only stains the virally infected cells allowing you to easily count the number of plaques.' This is a common misconception. Crystal violet stains viable cells; areas where virus has lysed cells (plaques) appear as clear zones against a stained monolayer. So the dye does not specifically stain infected cells, and plaques are identified as zones of cell death, not stained infected cells. This option mischaracterizes the staining pattern and would lead to counting errors.
Option 4: 'You can perform a plaque assay to measure the number of plaque-forming units in any given virus sample.' This statement captures the core purpose of a viral plaque assay: estimating the quantity of infectious units, expressed as plaque-forming units (PFU) per volume, by counting plaques formed by virus-induced cell lysis. It aligns with the fundamental objective of the assay and is conceptually correct when performed under appropriate conditions (proper dilutions, controls, and counting guidelines).
In summary, Option 1 misstates an optimization criterion, Option 2 describes an incorrect setup regarding virus vs. media volumes, Option 3 misrepresents the staining logic of crystal violet, and Option 4 correctly states the assay’s purpose of measuring PFU in a virus sample. The reasoning indicates why each of the first three choices is flawed and why the fourth choice accurately reflects the assay’s primary use.

MIMI2002 (ND) Tute-shop Quiz 5

Which of the following statements regarding a viral plaque assay is correct?

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