Question

A 2 year old child is brought to the emergency department with a history of fever and vomiting. On examination he has neck rigidity. CSF examination shows polymorphs more than 2000/microL, protein 100 mg/dL, and glucose 10 mg/dL. Gram stain shows Gram negative coccobacilli. Culture shows growth of bacteria only on chocolate agar and not on blood agar. The causative agent is

• A. Neisseria meningitidis
• B. Haemophilus influenzae
• C. Branhamella catarrhalis
• D. Legionella pneumophila

Hint:

Growth only on chocolate agar, not blood agar, means the organism needs both factor X and factor V: think Haemophilus influenzae.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The child has fever, vomiting, and neck rigidity, and the CSF picture (high polymorphs, high protein, low glucose) fits acute bacterial meningitis. We need the organism that matches the Gram stain shape and the odd growth pattern.

Step 2: Key Concept:
Chocolate agar is blood agar that has been heated during preparation. Heating lyses the red cells and destroys an enzyme called NADase, so it releases two growth factors: factor X (hemin) and factor V (NAD). Some bacteria need both factors and can only grow on chocolate agar, not on plain blood agar, where free V factor stays too low.

Step 3: Detailed Explanation:
Neisseria meningitidis is a Gram negative bean shaped diplococcus, not a coccobacillus, and it grows well on ordinary blood agar as well as chocolate agar, so it does not need the special growth factors described here. This rules out option (1).
Haemophilus influenzae is a small Gram negative coccobacillus that strictly needs both factor X and factor V to grow. It grows on chocolate agar but fails to grow on blood agar as a pure culture, matching the exact pattern given in the question. In an unimmunised 2 year old, H. influenzae type b is a classic cause of bacterial meningitis. This fits option (2) perfectly.
Branhamella catarrhalis, now called Moraxella catarrhalis, is a Gram negative diplococcus that grows on ordinary blood agar without needing X or V factor, and it is a rare cause of meningitis. This rules out option (3).
Legionella pneumophila is a Gram negative bacillus that needs a special charcoal yeast extract agar with cysteine and iron, not chocolate agar, and it causes atypical pneumonia, not this kind of meningitis picture. This rules out option (4).

Step 4: Final Answer:
The coccobacillary shape plus growth only on chocolate agar points to Haemophilus influenzae.
Hence, the correct answer is option (2).