**Core Concept**
The patient is likely suffering from severe bacterial meningitis, a life-threatening infection of the meninges that requires prompt diagnosis and treatment. This condition is characterized by inflammation of the meninges, leading to increased intracranial pressure and potentially irreversible brain damage.

**Why the Correct Answer is Right**
Severe bacterial meningitis requires immediate administration of antibiotics to target the causative pathogen. The most commonly used antibiotic for this condition is ceftriaxone, a third-generation cephalosporin with broad-spectrum activity against Gram-positive and Gram-negative bacteria. The treatment should be initiated as soon as possible, ideally within 30 minutes of diagnosis, to prevent further brain damage and improve outcomes.

**Why Each Wrong Option is Incorrect**

* **Option A:** Corticosteroids, such as dexamethasone, may be used in conjunction with antibiotics to reduce inflammation and prevent brain damage, but they should not be initiated as the first step of treatment.
* **Option B:** Imaging studies, such as CT or MRI scans, are crucial for confirming the diagnosis of bacterial meningitis and ruling out other causes of altered mental status. However, they should not be the next step in management.
* **Option C:** Lumbar puncture (LP) is essential for diagnosing bacterial meningitis, but it should not be performed until after the patient has received empirical antibiotic therapy.

**Clinical Pearl / High-Yield Fact**
In cases of suspected bacterial meningitis, it is essential to initiate empirical antibiotic therapy within 30 minutes of diagnosis. The most commonly used antibiotic is ceftriaxone, which should be administered intravenously as soon as possible.

**Correct Answer:** C.