Which medium should be used for susceptibility testing of Streptococcus pneumoniae?

Which medium should be used for susceptibility testing of Streptococcus pneumoniae?

• A. Mueller-Hinton base supplemented with 1% hemoglobin and 1% IsoVitaleX
• B. Mueller-Hinton base supplemented with 5% lysed horse blood
• C. Charcoal yeast extract agar
• D. Chocolate agar

Answer: (B)

Susceptibility testing for Streptococcus pneumoniae requires a blood-containing, nutrient-rich medium because this organism is fastidious and grows best with blood components that support consistent colony growth and reliable diffusion of antibiotics. Using Mueller-Hinton base with 5% lysed horse blood provides a standardized environment that promotes adequate pneumococcal growth and stable zone formation, which is essential for accurate disk diffusion results. Plain Mueller-Hinton agar without blood often yields poor or inconsistent growth for pneumococcus, making zone measurements unreliable. Media like charcoal yeast extract agar or chocolate agar are not standard diffusion media for routine susceptibility testing and can alter diffusion characteristics, so they’re not used for this purpose.

Susceptibility testing for Streptococcus pneumoniae requires a blood-containing, nutrient-rich medium because this organism is fastidious and grows best with blood components that support consistent colony growth and reliable diffusion of antibiotics. Using Mueller-Hinton base with 5% lysed horse blood provides a standardized environment that promotes adequate pneumococcal growth and stable zone formation, which is essential for accurate disk diffusion results. Plain Mueller-Hinton agar without blood often yields poor or inconsistent growth for pneumococcus, making zone measurements unreliable. Media like charcoal yeast extract agar or chocolate agar are not standard diffusion media for routine susceptibility testing and can alter diffusion characteristics, so they’re not used for this purpose.