Which organism is a gram-negative pleomorphic coccobacillus that requires X and V factors and grows on chocolate agar?

• A. Haemophilus influenzae
• B. Neisseria meningitidis
• C. Moraxella catarrhalis
• D. Streptococcus pneumoniae

Answer: (A)

This question tests recognition of the growth requirements that identify Haemophilus influenzae. This organism is a Gram-negative, pleomorphic coccobacillus that cannot synthesize certain growth factors, so it needs two external cofactors to grow: X factor (hemin) and V factor (NAD). Chocolate agar provides these factors by lysing blood cells and releasing them, allowing Haemophilus influenzae to grow readily. It can also show satellite growth on standard blood agar around Staphylococcus aureus colonies, which supply NAD. The other organisms listed do not fit this pattern: they are not pleomorphic coccobacilli requiring both X and V factors, and they have different growth characteristics (for example, some are Gram-positive or do not require these factors).