Okay, let's tackle this question about the Griffith experiment. The user provided the question but didn't list the options. Hmm. The correct answer is supposed to be something like Streptococcus pneumoniae, right? Because I remember that Griffith's experiment was about bacterial transformation using pneumococcus.

First, I need to recall the core concept. The experiment was pivotal in showing that DNA is the transforming principle. So the core concept here is bacterial transformation and the role of DNA as genetic material. Griffith used two strains of Streptococcus pneumoniae: the virulent S strain and the non-virulent R strain. He heat-killed the S strain and mixed it with live R strain, resulting in the death of mice, indicating that something from the dead S strain transformed the R strain into S.

Now, the options are missing, but the correct answer is Streptococcus pneumoniae. So in the explanation, I need to explain why this is correct. The experiment showed that the heat-killed S strain's DNA was responsible for transforming the R strain. The wrong options might include other bacteria like E. coli or something else, which aren't related to this experiment.

For the clinical pearl, it's important to remember that this experiment laid the groundwork for Avery, MacLeod, and McCarty's later work identifying DNA as the carrier of genetic material. Also, the concept of transformation is crucial in molecular biology techniques today.

I need to structure the explanation according to the user's guidelines. Make sure each section is clear and concise, using medical terminology. Check that the wrong options are addressed even though they're not listed, but the user probably expects common distractors. Maybe options like E. coli, Staphylococcus, or others. Explain why those are incorrect. For example, E. coli is commonly used in other experiments but not in Griffith's.

Also, the user wants the correct answer line at the end. Let me make sure the final answer is correctly formatted as per their instructions. Alright, putting it all together now.

**Core Concept**
The Griffith experiment demonstrated *bacterial transformation*, proving that genetic material (DNA) could be transferred between bacteria. It used *Streptococcus pneumoniae* to show that "transforming principle" from heat-killed virulent bacteria could convert non-virulent strains into virulent ones.

**Why the Correct Answer is Right**
Griffith observed that mice injected with a mixture of heat-killed virulent S strain *Streptococcus pneumoniae* and live non-virulent R strain died. This indicated that the R strain was transformed into the S strain by an unknown "transforming substance" (later identified as DNA). The experiment established the basis for understanding horizontal gene transfer in bacteria.

**Why Each Wrong Option is Incorrect**
**Option A:** *Escherichia coli* is not the organism used in Griffith’s experiment. It is commonly used in recombinant DNA studies but unrelated to this transformation experiment.
**Option B:** *Bacillus subtilis* is a model organism for sporulation studies, not transformation.
**Option C:** *Staphylococcus aureus* causes infections but was never the subject of Griffith’s work.

**Clinical Pearl / High-Yield Fact**
Griffith’s 1928 experiment was the first to suggest DNA as the genetic

✓ Correct Answer: B. Pneumococcus