For susceptibility testing of Streptococcus pneumoniae, which supplement is used with Mueller-Hinton broth?

For susceptibility testing of Streptococcus pneumoniae, which supplement is used with Mueller-Hinton broth?

• A. 1% hemoglobin and 1% IsoVitaleX
• B. Chocolate agar
• C. 5% lysed horse blood in Mueller-Hinton broth
• D. None of the above

Answer: (C)

Streptococcus pneumoniae is fastidious and needs enriched conditions to grow reliably in susceptibility tests. Mueller-Hinton broth alone often doesn’t support robust growth or accurate readings, so an enrichment is added. The standard supplement is 5% lysed horse blood, which provides nutrients and growth factors released from red blood cells that pneumococcus requires. This enrichment helps the organism grow well and yields stable, interpretable MIC or zone-size results, which is why it’s recommended for testing. The other options aren’t appropriate in this context: chocolate agar is a solid medium, not a broth supplement; 1% hemoglobin with IsoVitaleX is not the established enrichment for this purpose in broth; and there is a defined enrichment for this organism, so “none of the above” isn’t correct.

Streptococcus pneumoniae is fastidious and needs enriched conditions to grow reliably in susceptibility tests. Mueller-Hinton broth alone often doesn’t support robust growth or accurate readings, so an enrichment is added. The standard supplement is 5% lysed horse blood, which provides nutrients and growth factors released from red blood cells that pneumococcus requires. This enrichment helps the organism grow well and yields stable, interpretable MIC or zone-size results, which is why it’s recommended for testing. The other options aren’t appropriate in this context: chocolate agar is a solid medium, not a broth supplement; 1% hemoglobin with IsoVitaleX is not the established enrichment for this purpose in broth; and there is a defined enrichment for this organism, so “none of the above” isn’t correct.