**Core Concept**
A Gram-negative rod that is lactose positive and glucose fermenting is typically a member of the Enterobacteriaceae family, which includes various species of bacteria that can cause gastrointestinal infections. This organism's ability to ferment lactose and glucose is a key characteristic used in its identification.

**Why the Correct Answer is Right**
The isolated organism is likely *Escherichia coli* (E. coli), a common cause of gastrointestinal infections, including bloody diarrhea. E. coli is a Gram-negative rod that belongs to the Enterobacteriaceae family and is known for its ability to ferment lactose and glucose. The lactose positive result indicates that the organism can break down lactose, producing acid and causing the pH to decrease, which is a characteristic feature of *E. coli*. Glucose fermentation is another key feature of this organism, allowing it to metabolize glucose and produce energy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it doesn't specify a particular organism, making it a vague and unhelpful choice.
**Option B:** This option is incorrect because it doesn't match the description of the isolated organism. *Shigella* species are also Gram-negative rods, but they are lactose non-fermenters.

**Clinical Pearl / High-Yield Fact**
*E. coli* is a common cause of gastrointestinal infections, including urinary tract infections (UTIs), and is often associated with the consumption of undercooked ground beef or contaminated water.

**Correct Answer: C.**