Loeffler's serum medium is recommended for the cultivation of which organism?

• A. Abiotrophia sp.
• B. Corynebacterium diphtheriae
• C. Leuconostoc sp.
• D. Streptococcus agalactiae

Answer: (B)

Loeffler's serum medium is an enrichment medium chosen specifically for Corynebacterium diphtheriae because its nutrient-rich composition supports vigorous growth of this organism and promotes the formation of distinctive metachromatic (volutin) granules inside the cells. When you stain cells from this medium with Albert’s stain, those granules appear as blue or purple inclusions within the pink/violet cells, a hallmark feature that helps differentiate C. diphtheriae from other Gram-positive rods. The other organisms listed do not rely on Loeffler’s medium for growth, nor do they produce the characteristic metachromatic granules visible with this stain and medium, so this medium is best suited to cultivating C. diphtheriae.