Which of the following is true of Haemophilus spp.?

• A. Obligate parasites
• B. Grow well on sheep blood agar
• C. Small gram-negative diplococci
• D. Many are found as normal biota in the gastrointestinal tract.

Answer: (A)

Haemophilus species are fastidious bacteria that rely on nutrients provided by the host, specifically X (hemin) and V (NAD) factors, to grow. This dependence on host resources makes them behave like obligate parasites in practice, since they cannot thrive on ordinary media unless those factors are supplied. They do not grow well on plain sheep blood agar and instead require enriched media such as chocolate agar or blood agar supplemented with X and V factors (often showing satellitism around Staphylococcus colonies). They are small gram-negative coccobacilli, not diplococci, and they are not typical residents of the gastrointestinal tract but are more commonly found in the upper respiratory tract.