While researching microbial interactions, a student has taken the following notes:
- Antibiotic tolerance is a temporary physiological state, unlike heritable antibiotic resistance.
- Researchers exposed Escherichia coli to spent medium, the cell-free liquid collected from Pseudomonas aeruginosa cultures.
- Compared with E. coli in fresh medium, the exposed E. coli grew more slowly, and a greater proportion survived treatment with the antibiotic ciprofloxacin.
- In one experiment, researchers reset the dissolved oxygen and pH of wild-type P. aeruginosa spent medium to the levels in fresh medium; the effects on E. coli remained.
- In a separate experiment, spent medium from a mutant P. aeruginosa strain unable to produce the molecule pyocyanin did not cause the effects.
- Adding purified pyocyanin to the mutant strain's spent medium restored both slower growth and increased ciprofloxacin survival.
The student wants to make and support the claim that pyocyanin, rather than merely low oxygen or altered acidity, caused the temporary increase in E. coli's ciprofloxacin tolerance. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions, divide the stated goal into its required components and find the notes supporting each one. When notes describe multiple experiments, favor a choice that combines their conclusions accurately while preserving which treatment occurred in each experiment. Reject choices that merge separate trials, omit a required comparison, or overstate a temporary result as permanent.
Hints
Break the goal into two parts
Look for evidence that addresses the proposed molecule and separate evidence that rules out the two environmental conditions.
Look for loss and restoration
In causal research, an effect disappearing when a factor is removed and returning when that factor is restored provides especially relevant evidence.
Preserve the experimental design
Check whether each option accurately keeps the oxygen-and-pH experiment separate from the mutant-and-addition experiment. Also distinguish temporary tolerance from permanent resistance.
Step-by-step Explanation
Identify the required claim
The response must both identify pyocyanin as the cause and distinguish its effect from the possible effects of low oxygen or altered acidity.
Match each part of the claim with evidence
Resetting oxygen and pH while the effect remained weakens those conditions as alternative explanations. The absence of the effect with the pyocyanin-deficient mutant and its return after purified pyocyanin was added directly connect the effect to that molecule.
Check accuracy and scope
Choice B presents the experiments as separate but complementary evidence and correctly describes the outcome as temporary tolerance. It neither invents an experimental condition nor claims that E. coli became permanently resistant.