**Core Concept**
The question requires identification of a bacterial pathogen causing a newborn's sepsis, as indicated by difficulty in breathing, lethargy, inability to feed, and elevated total counts with polymorph predominance, along with growth of LF Mucoid colonies on MacConkey agar.

**Why the Correct Answer is Right**
The growth of LF (Lactose Fermenting) Mucoid colonies on MacConkey agar indicates the presence of a gram-negative bacterium that ferments lactose and produces a mucoid capsule. This description matches *Escherichia coli*, a common cause of neonatal sepsis. The mucoid colonies are likely due to the production of capsular polysaccharides, which confer virulence to the organism. The elevated total counts with polymorph predominance in the blood culture suggests a bacterial infection, and the clinical presentation of difficulty in breathing, lethargy, and inability to feed is consistent with sepsis caused by *E. coli*.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided. However, in the context of the question, it is likely that the correct answer is *E. coli*, which is not listed among the options.

**Clinical Pearl / High-Yield Fact**
The presence of mucoid colonies on MacConkey agar in a blood culture from a newborn with sepsis should raise suspicion for *E. coli* infection, which requires prompt antibiotic therapy.

**Correct Answer:** D. *Escherichia coli*