For disk diffusion testing of Haemophilus influenzae, which medium is recommended?

For disk diffusion testing of Haemophilus influenzae, which medium is recommended?

• A. Mueller-Hinton base supplemented with 5% sheep blood
• B. Chocolate agar
• C. Mueller-Hinton base supplemented with hematin, NAD, and yeast extract
• D. Charcoal yeast extract agar

Answer: (C)

Haemophilus influenzae is a fastidious organism that requires X and V growth factors to grow: hematin (X factor) and NAD (V factor). Disk diffusion testing depends on a medium that both supports bacterial growth and allows reliable diffusion of antibiotics to produce interpretable zone sizes. A Mueller-Hinton base supplemented with hematin, NAD, and yeast extract provides the necessary X and V factors plus additional nutrients, enabling robust growth of H. influenzae and consistent diffusion of antibiotics for accurate interpretation. Other media either lack these essential factors or introduce variables that can affect diffusion or growth, making them less suitable for this test.