A 2 years old child is brought to the emergency with history of fever and vomiting. On examination he has neck rigidity. The CSF examination shows polymorphs more that 2000/m1 protein 100 mg/dl and glucose 10mg/d1. The Gram stain shows the presence of Gram negative coccobacilli. The culture shows growth of bacteria only on chocolate agar and not on blood agar. The caustive agent is ?

**Core Concept**
Bacterial meningitis in children is often caused by Gram-negative bacteria, which can be identified by their growth characteristics and Gram stain appearance. The presence of high protein and low glucose levels in the cerebrospinal fluid (CSF) suggests bacterial infection.

**Why the Correct Answer is Right**
The presence of Gram-negative coccobacilli in the CSF, along with the specific growth characteristics on chocolate agar, points towards Haemophilus influenzae type b (Hib) as the causative agent. H. influenzae type b requires X (hemin) and V (nicotinamide adenine dinucleotide, NAD) factors for growth, which are provided by chocolate agar but not by blood agar. The high protein and low glucose levels in the CSF are consistent with bacterial meningitis caused by H. influenzae type b.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Neisseria meningitidis is a Gram-negative diplococcus, not a coccobacillus.
**Option B:** This option is incorrect because Streptococcus pneumoniae is a Gram-positive diplococcus, not a Gram-negative coccobacillus.
**Option C:** This option is incorrect because Escherichia coli is a Gram-negative rod, but it does not typically cause bacterial meningitis in children.

**Clinical Pearl / High-Yield Fact**
Remember that H. influenzae type b requires specific growth factors for its growth, and its Gram stain appearance is a coccobacillus shape.

**Correct Answer:** C.

✓ Correct Answer: B. Haemophilus influenzae