Haemophilus influenzae growth factors and culture media are best described by which statement?

• A. Haemophilus influenzae requires X and V factors; chocolate agar supports growth
• B. Haemophilus influenzae grows on MacConkey agar with lactose fermentation
• C. Haemophilus influenzae grows on blood agar without any special factors
• D. Haemophilus influenzae is a Gram-positive diplococcus

Answer: (A)

Haemophilus influenzae is a fastidious organism that needs two growth factors to grow: X (hemin) and V (NAD). Chocolate agar is prepared by lysing red blood cells, which releases both X and V into the medium, allowing H. influenzae to grow. This makes the statement describing growth on chocolate agar with X and V factors the best description. On MacConkey agar, it doesn’t reliably grow and certainly doesn’t routinely ferment lactose, so that option isn’t appropriate. Blood agar without any enrichment lacks the required factors, so growth would be poor or absent. And this organism is a Gram-negative coccobacillus, not a Gram-positive diplococcus, so that descriptor is incorrect.