Nutrient media used for bacterial cultures are called

• A. Broth
• B. Gelatin
• C. Agarose
• D. Agar

Answer: (D)

Solid media used to grow bacterial cultures rely on agar as the gelling agent. Agar is a seaweed-derived polysaccharide that melts when heated and sets into a firm gel at incubation temperatures, providing a stable surface for colonies to form. The nutrients themselves come from the nutrient medium mixed with the agar, like nutrient agar or trypticase soy agar.

Agarose, while similar in being a gel, is mainly used for procedures like gel electrophoresis and does not supply nutrients for growth. Gelatin can form a solid-like gel but liquefies at moderate temperatures and many bacteria can digest it, making it unreliable as a solid culture medium. Broth is a liquid nutrient medium, not a solid one.