Haemophilus spp. growth requirements are best described by which statement?

• A. Haemophilus influenzae requires X and V factors and grows on chocolate agar
• B. Haemophilus influenzae grows best on ordinary sheep blood agar
• C. Haemophilus influenzae is a lactose-fermenting organism on MacConkey agar
• D. Haemophilus influenzae is a Gram-positive coccus

Answer: (C)

Haemophilus species are fastidious bacteria that depend on specific growth factors to multiply. They require X factor (hemin) and V factor (NAD). Chocolate agar provides both factors because the heating of blood cells releases them, allowing Haemophilus to grow readily. Ordinary sheep blood agar lacks enough X and V, so Haemophilus won’t grow well there. On MacConkey agar, Haemophilus influenzae does not ferment lactose and typically does not grow, since MacConkey does not supply X and V; this makes the idea that it is a lactose-fermenter on MacConkey incorrect. Additionally, Haemophilus influenzae is a Gram-negative coccobacillus, not a Gram-positive coccus. Therefore, the description that best reflects its growth requirements is that it needs X and V factors and grows on chocolate agar.