In a standard broth dilution, what is the most commonly used visual indicator that bacteria have grown in a tube or well?

• A. A bright color change to blue in the broth caused by antibiotics binding to amino acids released by bacteria, which is the standard colorimetric growth indicator used universally.
• B. Visible turbidity (cloudiness) of the broth indicating bacterial proliferation.
• C. Formation of crystalline precipitates in the broth as bacteria metabolize the antibiotic into insoluble products.
• D. Complete clearing of the broth due to production of extracellular enzymes that digest the medium constituents.

Answer: (B)