Which growth factors are required by Haemophilus influenzae in culture?

• A. Glucose and galactose
• B. Vitamin K and iron
• C. Cobalt and zinc
• D. X factor and V factor

Answer: (D)

Haemophilus influenzae is a fastidious organism that must be provided with specific growth factors from its environment. It needs two external nutrients: X factor (heme) and V factor (NAD). X factor supplies heme for essential enzymes, while V factor provides NAD, a key coenzyme for many reactions. The bacterium cannot make enough NAD on its own, so growth depends on receiving both factors from the medium. Media like chocolate agar or blood agar with lysed cells release these factors, enabling growth; the nearby presence of Staphylococcus aureus can also supply V factor through NAD released from lysed cells, illustrating the satellite phenomenon. Other nutrients such as simple sugars or vitamin K with iron do not fulfill the requirement. Therefore, the growth factors required are X factor and V factor.