**Core Concept**
Conjunctivitis in newborns is a common condition characterized by inflammation of the conjunctiva, the thin membrane covering the white part of the eyes and the inside of the eyelids. This condition can be caused by various factors, including viral, bacterial, or chemical agents.

**Why the Correct Answer is Right**
The correct answer is **Neisseria gonorrhoeae**. This bacterium is a leading cause of conjunctivitis in newborns, often acquired during passage through an infected birth canal. The bacteria can cause severe inflammation and potentially lead to vision loss if left untreated. Neisseria gonorrhoeae infects the conjunctiva by adhering to the mucosal surface and invading the epithelial cells.

**Why Each Wrong Option is Incorrect**
**Option A:** **Staphylococcus aureus** is a common cause of bacterial conjunctivitis in adults but is less commonly associated with newborn conjunctivitis.

**Option B:** **Adenovirus** is a common cause of viral conjunctivitis in all age groups, including newborns. However, it is not the most common cause of conjunctivitis in newborns.

**Option C:** **Herpes simplex virus** can cause conjunctivitis in newborns, but it is not the most common cause.

**Clinical Pearl / High-Yield Fact**
Newborns with conjunctivitis should be evaluated promptly, as delayed treatment can lead to vision loss and other complications. A thorough maternal history, including any previous sexually transmitted infections, is essential in determining the cause of conjunctivitis in newborns.

**Correct Answer: D. Neisseria gonorrhoeae**